Post on 16-Apr-2022
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Ecole Doctorale Science et Ingénierie
De l’Université de Cergy-Pontoise
THESE
Pour obtenir le grade de docteur de l’Université de Cergy-Pontoise
Spécialité: Chimie des matériaux
Cardanol: a bio-based building block for new
sustainable and functional materials
Présentée par
Laura Puchot
Laboratoire de Physico-chimie des Polymères et des Interfaces, EA 2528
Soutenue le 14 décembre 2016 devant le jury composé de :
Etienne Fleury, Professeur à l’INSA de Lyon Rapporteur
Florent Allais, Professeur à AgroParis Tech de Reims Rapporteur
Naceur Belgacem, Professeur à l’INP-Pagora de Grenoble Président du jury
Valérie Langlois, Professeur à l’Université Paris Est Créteil Examinateur
Frédéric Vidal, Professeur de l’Université de Cergy-Pontoise Directeur de thèse
Cédric Vancaeyzeele, Maître de conférences de l’Université de Cergy-Pontoise Co-encadrant
Pierre Verge, Ingénieur de recherche à LIST Co-encadrant
Youssef Habibi, Ingénieur de recherche à LIST Co-encadrant
René Saint Loup, Responsable département chimie des polymères chez Roquette Invité
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Abstract
Recently, considerable interest of the chemistry of renewable ressources and their resulting
materials has grown with a view to reduce the use of finite petroleum-based resources. The
present thesis entitled « Cardanol: a bio-based building block for new sustainable and
functional materials » is dealing with the chemical modification of cardanol and its use for
various applications. Cardanol is a naturally occurring phenolic compound issued from cashew
nutshell liquid. Its chemical structure is interesting because cardanol is bearing a phenolic
hydroxyl function and an unsaturated alkyl chain in meta. Numerous chemical reactions can thus
be considered for its chemical modification.
The first part of this study is dealing with the synthesis and the characterization of three cardanol-
based ammonium surfactants differing by their amine functionalities content. Their effectiveness
on the exfoliation of silicate clay within an epoxy matrix was investigated with the aim to
elaborate composite materials.
The second chapter is describing a novel method for the synthesis of bio-based benzoxazine
monomers and the elaboration of polybenzoxazine networks issued from cardanol. A new
generation of benzoxazine monomers issued from cardanol or from lignin derivatives such as
vanillin were recently developed. However, up to now, the majority of the synthetised
benzoxazine monomers are mainly mono-functionnal or display too high melting temperatures.
The elaboration of valuable self-standing materials is thus strongly impeded. To solve this
problem, an innovative synthesis of asymmetric benzoxazine monomers by combination of
cardanol and lignin derivatives is described. The resulting self-standing materials display
improved properties in comparison to materials issued from symmetric bio-based monomers.
Finally, the third chapter realtes to the use of a cardanol-based epoxy pre-polymer for the
elaboration of bio-based epoxy materials. Nevertheless, this new material displays low Tg due to
the alkyl side chain of cardanol in addition to low water uptake. In order to reinforce the thermo-
mechanical properties of the material and to reduce its water uptake, a chemical modification
was achieved at the macromolecular scale by the elaboration of interpenetrating polymer
networks with polybenzoxazine networks.
These various studies allowed to highlight the easy and versatile modification of cardanol,
resulting thus in a diversity of bio-based synthons and their resulting materials. This work paves
the way to the elaboration of other chemical structures and molecular architectures for various
applications.
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Résumé:
Récemment, la chimie des ressources renouvelables et les matériaux qui en découlent ont suscités
un intérêt considérable dans le but de limiter l’utilisation des ressources fossiles. La présente
thèse intitulée « Cardanol : a bio-based building block for new sustainable and functional
materials » traite de la modification chimique du cardanol et de son utilisation dans diverses
applications. Le cardanol est un dérivé phénolique naturel extrait de l’huile de coque de noix de
cajou. Sa structure chimique est intéressante : il est substitué d’une chaîne alkyle en C15,
partiellement insaturée, et il est porteur d’une fonction phénol, permettant d’envisager de
nombreuses réactions chimiques.
La première partie de cette étude traite de la synthèse et de la caractérisation de trois surfactants
ammoniums issus du cardanol se différenciant par le degré de substitution de leurs amines. Leur
capacité à favoriser l’exfoliation d’une argile lamellaire dans une matrice de type époxy a été
étudiée dans le but de concevoir des matériaux composites.
Le second chapitre décrit une nouvelle méthode de synthèse de monomères benzoxazines bio-
basés et l’élaboration de réseaux polybenzoxazines à partir du cardanol. Une nouvelle génération
de monomères benzoxazine, issus du cardanol ou de dérivés de la lignine tels que la vanilline, a
récemment été développée. Cependant l’essentiel des benzoxazines bio-basées synthétisées
jusqu’à présent sont monofonctionnelles ou présentent des températures de fusion trop élevées.
Elles ne permettent donc pas l’élaboration de matériaux autosupportés valorisables. Afin de
pallier ce problème, une synthèse originale de monomères benzoxazines asymétriques, reposant
sur la combinaison de cardanol et de dérivés de la lignine, est décrite. Les matériaux
autosupportés résultants présentent des propriétés améliorées par rapport à celles que ne
pourraient atteindre les monomères symétriques issus de ces phénols bio-sourcés.
Finalement, le troisième chapitre concerne l’utilisation d’un pré-polymère époxy issu du cardanol
pour l’élaboration de matériaux époxy bio-basés. Cependant, ce nouveau matériau présente une
faible Tg en raison de la chaîne alkyle du cardanol et une faible prise en eau. Afin de renforcer ses
propriétés thermo-mécaniques et de diminuer sa prise en eau, une modification chimique a été
réalisée à l’échelle macromoléculaire par l’élaboration de réseaux interpénétrés de polymères à
base de réseaux polybenzoxazines.
Ces différents travaux ont permis de mettre en avant la modification aisée et versatile du
cardanol, pouvant ainsi résulter en une large variété de synthons bio-basés et des matériaux qui
en découlent. Ces travaux ouvrent la voie vers d’autres structures et architectures moléculaires
aux applications nombreuses.
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Remerciements
J’adresse mes sincères remerciements au Professeur Frédéric Vidal, directeur du Laboratoire de
Physico-Chimie des Polymères et des Interfaces, pour son accueil au sein de son laboratoire afin de
réaliser mes travaux de thèse et pour son encadrement durant ces trois années.
Je tiens à remercier particulièrement Docteur Pierre Verge pour son encadrement de tous les jours
au sein du Luxembourg Institute of Science and Technology, pour son soutien, sa disponibilité, son
aide et ses conseils tout au long de ma thèse. Je remercie également les Docteurs Cédric Vancaeyzeele
et Youssef Habibi pour leur implication dans ces travaux et pour leur support.
Je souhaite exprimer ma reconnaissance aux membres du jury de thèse, Pr. Etienne Fleury, Pr.
Florian Allais, Pr. Valérie Langlois, Pr. Naceur Belgacem et Dr. René Saint-Loup, d’avoir accepté
d’évaluer ce travail.
Je souhaite égalament remercier tous les membres du département matériaux au sein du LIST,
passés et présents, pour l’aide et le soutien qu’ils m’ont apporté. Je remercie tout particulièrement
mes collègues et les anciens doctorants ainsi que les nouveaux pour leur bonne humeur et les
agréables moments passés avec eux aussi bien au laboratoire qu’en dehors.
Je tiens aussi à remercier tous les membres du LPPI pour leur accueil chaleureux à chacune de mes
visites. Je les remercie également pour leur aide et leurs conseils.
Enfin je remercie infiniment mes parents, Christophe et Michaele, ma sœur, Julia, et mon conjoint,
Habib, pour leur soutien durant ces années.
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Contents
List of Abbreviations ................................................................................................................................... 10
List of Figures ................................................................................................................................................. 13
List of Tables .................................................................................................................................................. 20
General Introduction and Context .......................................................................................................... 22
Chapter I: Introduction ............................................................................................................................... 25
1 Cashew nutshell liquid: extraction and composition ............................................................. 25
2 Extraction of cardanol from CNSL and reactivity ..................................................................... 27
3 Cardanol based chemicals and functional molecules ............................................................. 30
3.1 Plasticizers and reactive diluents ........................................................................................................ 30
3.2 Surfactants .................................................................................................................................................... 32
3.2.1 Anionic surfactants .......................................................................................................................... 33
3.2.2 Non-ionic surfactants ...................................................................................................................... 35
3.2.3 Cationic surfactants ......................................................................................................................... 36
3.3 Curing agents ............................................................................................................................................... 37
3.4 Antioxidant ................................................................................................................................................... 40
4 Cardanol-based polymers ................................................................................................................. 42
4.1 Phenolic resins ............................................................................................................................................ 43
4.2 Polyurethane resins .................................................................................................................................. 44
4.2.1 Synthesis of cardanol-based polyols ........................................................................................ 44
4.2.2 Cardanol-based non-isocyanate PU .......................................................................................... 48
4.3 Epoxy resins ................................................................................................................................................. 49
4.4 Polybenzoxazine resins ........................................................................................................................... 51
5 Conclusion .............................................................................................................................................. 52
Chapter II: Surfactants from cardanol .................................................................................................. 53
1 Introduction........................................................................................................................................... 53
1.1 Preparation of nanocomposite materials ......................................................................................... 53
1.2 Structure and properties of clay and layered silicates as fillers ............................................. 54
1.3 Clay organomodification strategies .................................................................................................... 57
1.3.1 Clay organomodification by cationic exchange reaction .................................................. 57
1.3.2 Clay organomodification by cationic exchange reaction and covalent grafting ..... 59
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1.4 Cationic surfactants from Cardanol .................................................................................................... 60
2 Results and discussion ....................................................................................................................... 62
2.1 Surfactants synthesis ................................................................................................................................ 62
2.2 Characterization of CardSx surfactants ............................................................................................. 63
2.2.1 Fourier Transform Infrared spectroscopy (FTIR) .............................................................. 63
2.2.2 Characterization by 1H NMR ........................................................................................................ 64
2.2.3 Characterization by MALDI-TOF/MS ....................................................................................... 69
2.3 MMT clay organomodification and characterization .................................................................. 72
2.3.1 O-MMT preparation procedure .................................................................................................. 72
2.3.2 Characterization of O-MMT by X-ray diffraction (XRD) ................................................... 72
2.3.3 Characterization of O-MMT by MALDI-TOF/MS .................................................................. 73
2.4 Evidence of the surfactant amino-multifunctionnality within MMT clay ........................... 75
2.5 Preparation and characterization of CPN materials .................................................................... 77
2.5.1 CPN preparation procedure ......................................................................................................... 77
2.5.2 CPN characterization by X-ray diffraction (XRD) ................................................................ 78
2.5.3 CPN Thermal characterisation .................................................................................................... 79
2.5.4 CPN characterization by SEM and EDX analyses ................................................................. 82
3 Conclusions ............................................................................................................................................ 83
Chapter III: Benzoxazines from cardanol ............................................................................................ 85
1 Introduction........................................................................................................................................... 85
1.1 Benzoxazine thermosets ......................................................................................................................... 85
1.1.1 Generalities ......................................................................................................................................... 85
1.1.2 Benzoxazine polymerization ....................................................................................................... 87
1.1.3 Effect of hydrogen bonding and π-π supramolecular interactions on
polybenzoxazines properties .......................................................................................................................... 89
1.1.4 Polymerization catalysis ................................................................................................................ 91
1.1.5 Focus on di-benzoxazine monomers ........................................................................................ 93
1.2 Synthesis of Class B benzoxazines ...................................................................................................... 94
1.2.1 Electron donating and withdrawing effect ............................................................................ 94
1.2.2 Flexibility of the bridging diamine ............................................................................................ 94
1.3 Thermal properties of Class B di-Bz monomers and PBz resins ............................................ 95
1.3.1 Flexibility and chain length of the bridging diamine ......................................................... 95
1.3.2 Additional functional groups ....................................................................................................... 98
1.4 Bio-based benzoxazine: State of the art ........................................................................................... 99
1.4.1 Vanillin ................................................................................................................................................ 100
1.4.2 Guaïacol .............................................................................................................................................. 104
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1.4.3 Lignin-derivatives .......................................................................................................................... 104
1.4.4 Eugenol ............................................................................................................................................... 107
1.4.5 Coumarin ............................................................................................................................................ 109
1.4.6 Cardanol ............................................................................................................................................. 110
1.4.7 Urushiol .............................................................................................................................................. 113
1.5 Asymmetric benzoxazine monomers............................................................................................... 115
1.5.1 State of the art .................................................................................................................................. 115
2 Results and discussion .................................................................................................................... 117
2.1 Symmetric benzoxazine monomers synthesis and characterization ................................. 118
2.1.1 Symmetric Bz monomer synthesis .......................................................................................... 118
2.1.2 Characterization by 1H NMR ...................................................................................................... 118
2.1.3 Characterization by MALDI-TOF/MS or HRMS .................................................................. 124
2.1.4 Characterization by DSC and TGA............................................................................................ 127
2.1.5 Characterization by rheology analysis ................................................................................... 130
2.2 Asymmetric benzoxazine monomers synthesis and characterization............................... 132
2.2.1 Asymmetric Bz monomer synthesis ....................................................................................... 132
2.2.2 Characterization by 1H NMR ...................................................................................................... 133
2.2.3 Characterization by MALDI-TOF/MS ..................................................................................... 136
2.2.4 Characterization by DSC .............................................................................................................. 138
2.2.5 Characterization by rheology analysis ................................................................................... 139
2.3 Materials elaboration and characterizations ................................................................................ 141
2.3.1 Materials elaboration .................................................................................................................... 141
2.3.2 DMA characterization ................................................................................................................... 141
3 Conclusions ......................................................................................................................................... 143
Chapter IV: Interpenetrating Polymer Networks (IPN) from a cardanol-based thermoset
network ......................................................................................................................................................... 146
1 Introduction........................................................................................................................................ 146
1.1 Cashew nutshell diglycidyl ether ....................................................................................................... 147
1.2 CDGE-based thermosets ........................................................................................................................ 149
1.3 Reinforcement strategies: macromolecular reinforcement of epoxy networks ............ 152
1.3.1 State of the art of the epoxy/benzoxazine based co-networks ................................... 152
1.4 Epoxy/polybenzoxazine IPNs ............................................................................................................. 154
2 Results and discussion .................................................................................................................... 158
2.1 Choice of the system ............................................................................................................................... 158
2.1.1 Sequential in-situ preparation of IPN ..................................................................................... 158
2.1.2 Determination of the Bz monomer .......................................................................................... 159
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2.1.3 Determination of the suitable di-amine hardener ............................................................ 160
2.2 Curing profile for the elaboration of poly(CDGE)/poly(EDBz) IPNs .................................. 163
2.2.1 First step curing .............................................................................................................................. 164
2.2.2 Full curing profile ........................................................................................................................... 166
2.3 Poly(CDGE)/poly(EDBz) IPNs ............................................................................................................ 166
2.3.1 Poly(CDGE)/poly(EDBz) IPN Material elaboration .......................................................... 166
2.3.2 Thermo-mechanical properties of IPN materials .............................................................. 167
2.3.3 Estimation of the morphology by theoretical models ..................................................... 170
2.3.4 Behaviour toward water exposure ......................................................................................... 172
3 Conclusion ........................................................................................................................................... 174
General Conclusion and Perspectives ................................................................................................ 177
Annex: Materials and Methods ............................................................................................................. 180
1 Chapter II: Surfactants from cardanol ....................................................................................... 180
1.1 Materials ...................................................................................................................................................... 180
1.2 Characterization methods .................................................................................................................... 180
1.2.1 NMR analysis .................................................................................................................................... 180
1.2.2 Mass analysis .................................................................................................................................... 180
1.2.3 XRD analysis ..................................................................................................................................... 181
1.2.4 SEM analyis ....................................................................................................................................... 181
1.2.5 DSC analysis ...................................................................................................................................... 181
1.3 Surfactant synthesis ................................................................................................................................ 181
1.3.1 Synthesis and purification of CardS1 ..................................................................................... 181
1.3.2 Synthesis and purification of CardS2 ..................................................................................... 182
1.3.3 Synthesis and purification of CardS3 ..................................................................................... 182
1.4 MMT clay organomodification ............................................................................................................ 183
1.5 Reaction of the intercalated surfactants with Fge ...................................................................... 183
1.6 Clay mineral-based polymer nanocomposite (CPN) preparation ........................................ 183
2 Chapter III: Benzoxazines from cardanol ................................................................................ 183
2.1 Materials ...................................................................................................................................................... 183
2.2 Characterization methods .................................................................................................................... 184
2.2.1 NMR analysis .................................................................................................................................... 184
2.2.2 Mass analysis .................................................................................................................................... 184
2.2.3 DSC analysis ...................................................................................................................................... 184
2.2.4 Rheology analysis ........................................................................................................................... 185
2.2.5 DMA analysis .................................................................................................................................... 185
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2.2.6 TGA analysis ..................................................................................................................................... 185
2.3 Synthesis of the Bz monomers ............................................................................................................ 185
2.3.1 Synthesis of the di-cardanol Bz monomer ........................................................................... 185
2.3.2 Synthesis of the di-vanillin Bz monomer .............................................................................. 186
2.3.3 Synthesis of the di-phenol Bz monomer ............................................................................... 186
2.3.4 Synthesis of the Vani-Card asymmetric Bz monomer ..................................................... 186
2.4 Material elaboration ............................................................................................................................... 187
3 Chapter IV: Interpenetrating Polymers Networks (IPN) from cardanol-based
thermoset networks ................................................................................................................................. 187
3.1 Materials ...................................................................................................................................................... 187
3.2 Characterization methods .................................................................................................................... 187
3.2.1 DSC analysis ...................................................................................................................................... 187
3.2.2 Solvent extraction........................................................................................................................... 187
3.2.3 DMA analysis .................................................................................................................................... 188
3.3 Material elaboration ............................................................................................................................... 188
Annex: Figures ............................................................................................................................................ 189
References .................................................................................................................................................... 191
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List of Abbreviations
AAF Available Amino Functionalities
BADGE Bisphenol A Diglycidyl Ether
BTH Butyl Hydroxyl Toluene
Bz Benzoxazines
CA Coumaric Acid
CDGE Diglycidyl Ether of Cardanol
CEC Cation Exchange Capacity
CHCA α-cyano 4-hydroxycinnamic acid
CMC Critical Micelle Concentration
CNSL Cashew Nutshell Liquid
CNT Carbon Nanotubes
CPN Clay mineral-based polymer nanocomposite
DAC Diaminocyclohexane
DCTB Trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile
DDBS Dodecylbenzene Sulfonate
DDM 4,4’-diaminodiphenyl methane
DEHP Di-Ethyl-Hexyl-Phtalate
DETA Diethylenetriamine
di-Bz Di-Benzoxazine Monomers
DMA Dynamic Mechanical Analysis
DMEDA N,N-dimethylethylenediamine
DOP Dioctyl Phthalate
DSC Differential Scanning Calorimetry
DTA Differential Thermal Analysis
EC Extracted Content
EDA Ethylene Diamine
EDX Energy Dispersive X-Ray Analysis
EEW Epoxy Equivalent Weight
FA Ferulic Acid
Fge Furfuryl Glycidyl Ether
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FTIR Fourier Transform Infrared Spectroscopy
HAD Hexamethylenediamine
HRMS High Resolution Mass Spectrometry
IPD Isophorone Diamine
IPN Interpenetrating Polymer Network
MALDI Matrix-Assisted Laser Desorption/Ionization
m-Bz Mono-Benzoxazine Monomers
MLO Mineral Lubricant Oil
MMT Montmorillonite
MS Mass analysis
MS/MS Tandem Mass Spectrometry
NMR Nuclear Magnetic Resonance Spectroscopy
O-MMT Oragnomodified Montmorillonite
PA Phloretic Acid
PANI Polyaniline
PBz Polybenzoxazine
PMMA Poly(methyl methacrylate)
POSS Polyhedral Oligomeric Silesquioxanes
PU Polyurethanes
PVC Polyvinyl Chloride
ROP Ring-Opening Polymerization
SC Sulfonate Cardanol Surfactant
SDS Sodium Dodecyl Sulfonate
SEC Size Exclusion Chromatography
SEM Scanning Electron Microscopy
T5% 5 wt% Loss Temperature
TAEA Tris(2-aminoethyl)amine
Tamb Ambient Temperature
Tg Glass transition Temperature
TGA Thermogravimetric Analysis
Tm Melting Temperature
TOF Time-Of-Flight
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Tp Polymerization Temperature
XRD X-Ray Diffraction
ΔTproc Processing Window
13
List of Figures
Figure 1. Global production capacities of bioplastics (In 2013 and forecast for 2018).2 ............... 22
Figure I - 1. Main cashew nut producing countries in 2012. ...................................................................... 25
Figure I - 2. Representation of cashew apples. ................................................................................................ 25
Figure I - 3. Cross section of a cashew nut and nutshell. ............................................................................. 26
Figure I - 4. Chemical structure of CNSL components a) anacardic acid, b) cardanol, c) cardol
and d) 2-methylcardol. ................................................................................................................................................ 26
Figure I - 5. Anacardic acid decarboxylation. ................................................................................................... 27
Figure I - 6. Average compositions of the cardanol alkyl side chain. ...................................................... 28
Figure I - 7. Representation of the possible chemical modifications on the three reactive sites of
cardanol. ............................................................................................................................................................................ 28
Figure I - 8. Fine chemicals and functional molecules from cardanol. ................................................... 29
Figure I - 9. Schematic representation of polymer matrix a) plasticizer-free and b) in presence
of a plasticizer. ................................................................................................................................................................ 30
Figure I - 10. Chemical structure of mono-epoxidized cardanol NC-513 from Cardolite. ............. 32
Figure I - 11. Chemical structures of cardanol polyepoxy derivatives plasticizers.18 ..................... 32
Figure I - 12. Schematic representation of the various types of surfactants a) cationic, b)
anionic, c) non-ionic and d) zwitterionic. ............................................................................................................ 33
Figure I - 13. Synthesis of cardanol sulfonate surfactants.30 ...................................................................... 34
Figure I - 14. Synthesis of cardanol diazonium sulfonate surfactant.44 ................................................. 34
Figure I - 15. Chemical structure of cardanol carbonate surfactant.45 ................................................... 34
Figure I - 16. Chemical structure of sulfonated acrylate cardanol surfactants a) sulfonated-3-
pentadecyl phenyl acrylate and b) sodium-2-acryloxy ethan-1-oxy(3-pentedecyl) benzene
sulfonate.47 ....................................................................................................................................................................... 35
Figure I - 17. Chemical structure of cardanol polyethoxylate surfactants.27, 48 .................................. 36
Figure I - 18. Chemical structure of cardanol quaternary ammonium salt surfactants.49 ............. 36
Figure I - 19. Synthesis of cardanol ammonium salt surfactants.51 ......................................................... 37
Figure I - 20. Synthesis of cardanol phenalkamine curing agent.52 ......................................................... 37
Figure I - 21. Chemical structure of phenalkamine component from a) hexamethylenediamine
and b) diethylenetriamine.55 ..................................................................................................................................... 38
Figure I - 22. Synthesis of phenalkamine compounds from cardanol with varying molecular
weight and amine content.56 ..................................................................................................................................... 38
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Figure I - 23. Synthesis of cardanol-based phenalkamine compound by thiol-ene chemistry.16 39
Figure I - 24. Chemical structures of a) cardanol-cysteamine, and b) commercial NX-5454
phenalkamine. ................................................................................................................................................................. 40
Figure I - 25. Chemical structures of cardanol-based antioxidants. ....................................................... 40
Figure I - 26. Synthesis of cardanol-based phenolic resin.63 ...................................................................... 43
Figure I - 27. Condensation of cardanol with furfural and para-hydroxyacetophenone.66 ........... 43
Figure I - 28. Synthesis of a polyurethane. ........................................................................................................ 44
Figure I - 29. Chemical structures of cardanol-based diols a)72 b)73 c)69. ............................................. 45
Figure I - 30. Synthesis of cardanol-based polyol by reaction with oxazolidine.74 ........................... 45
Figure I - 31. Synthesis of cardanol-based polyols by reaction with melamine and di-
ethanolamine.75 .............................................................................................................................................................. 46
Figure I - 32. Synthesis of cardanol-based polyols by reaction with epichlorohydrin and
diethanol amine or with glycerol monochlorohydrin.73 ................................................................................ 46
Figure I - 33. Synthesis of cardanol-based polyols by performic acid oxidation.76 .......................... 47
Figure I - 34. Synthesis of cardano-based polyols by thiol-ene coupling with 2-
mercaptoethanol.77 ....................................................................................................................................................... 48
Figure I - 35. Synthesis of CNSL-based urethane polyols via a non-isocyanate route.78 ................ 49
Figure I - 36. Chemical structure of diglycidyl ether of cardanol – commercially available NC514
- from Cardolite Corporation. ................................................................................................................................... 49
Figure I - 37. Proposed reaction between epoxy groups of cardanol and carboxyl-terminated
polybutadiene.22 ............................................................................................................................................................. 50
Figure I - 38. Synthesis of epoxidized cardanol pre-polymer.25 ............................................................... 50
Figure I - 39. Synthesis of epoxidized cardanol and polycardanol. 80 .................................................... 51
Figure I - 40. Synthesis of a benzoxazine monomer.81 .................................................................................. 52
Figure II - 1. Schematic representation of a) MMT multi-scale organization,93 and b) MMT
crystallographic structure.89 ..................................................................................................................................... 55
Figure II - 2. Schematic representation of a) phase separated microcomposites, b) intercalated
nanocomposites, and c) exfoliated nanocomposites. ..................................................................................... 56
Figure II - 3. Schematic representation of the monomer inclusion within MMT, followed by in-
situ polymerization to reach MMT exfoliation. ................................................................................................. 58
Figure II - 4 Grafting of an amino-silane compound on prior organomodified MMT clay.108....... 60
Figure II - 5. Chemical structure of cardanol-based quaternary ammonium surfactant from De
Avellar et al.49 .................................................................................................................................................................. 60
15
Figure II - 6. Synthesis of cardanol-based ammonium surfactant from the cardanol mono-epoxy
derivative NC-513.51 ..................................................................................................................................................... 61
Figure II - 7. Scanning Electron Micrographs of BADGE/DAC polymer network filled with a) 5
wt% neat sepiolite and b) 5 wt% sepiolite organomodified by PkH+.51 ................................................. 61
Figure II - 8. Schematic representation of the synthesis of the Cardanol-based surfactants. ...... 63
Figure II - 9. FTIR spectra of a) CardS1, b) CardS2, c) CardS3................................................................... 64
Figure II - 10. CardS1 1H NMR spectrum (Solvent CDCl3). .......................................................................... 65
Figure II - 11. CardS2 1H NMR spectrum (Solvent CDCl3). .......................................................................... 67
Figure II - 12. CardS3 1H NMR spectrum (Solvent CDCl3). .......................................................................... 68
Figure II - 13. MALDI-MS spectra of CardS1 using a) CHCA & b) DCTB as matrix, CardS2 using c)
CHCA & d) DCTB and CardS3 using e) CHCA & f) DCTB as matrix. ........................................................... 70
Figure II - 14. Proposed mechanism for DCTB adduction to an aliphatic primary amine.113....... 71
Figure II - 15. X-Ray diffractograms of pristine MMT and O-MMT.......................................................... 73
Figure II - 16. MALDI-MS spectra, using DCTB-Ag as matrix, of a) CardS1-MMT, b) CardS2-MMT,
and c) CardS3-MMT. ..................................................................................................................................................... 74
Figure II - 17. Chemical structure of furfuryl glycidyl ether (Fge). ......................................................... 75
Figure II - 18. Reaction between epoxy and primary and secondary amine functions. ................. 75
Figure II - 19. MALDI-MS spectra of Fge-grafted a) CardS1-MMT, b) CardS2-MMT, and c)
CardS3-MMT using DCTB-Ag as matrix. ............................................................................................................... 76
Figure II - 20. X-ray diffractograms of CPN prepared with 10 mass% of pristine and
organomodified MMT by CardS1, CardS2 and CardS3. .................................................................................. 78
Figure II - 21. DSC thermograms of BADGE/DAC and CPN prepared with 5, 7, and 10 wt% of
pristine MMT. .................................................................................................................................................................. 80
Figure II - 22. DSC thermograms of BADGE/DAC and CPN prepared with 5, 7, and 10 wt% of
MMT modified by CardS1. .......................................................................................................................................... 81
Figure II - 23. I) Scanning electron micrographs of the fracture of MMT-CardS3 (above part)
and MMT-CardS1 (bottom part) based CPN. a) corresponds to the topographic micrographs, b)
to the chemical contrast (BSE detector, the lightest the points and the heaviest the elements)
and c) is the aluminium distribution of the analysed area ........................................................................... 82
Figure III - 1. Classical two-step approach for the synthesis of mono-benzoxazine monomers.120
............................................................................................................................................................................................... 86
Figure III - 2. Chemical structure of a) mono-benzoxazine (m-Bz) and b) di-benzoxazine (di-Bz)
monomers. ........................................................................................................................................................................ 86
Figure III - 3. Thermally-induced ring opening polymerization of Bz monomers.120 ...................... 87
16
Figure III - 4. Dimer product of para-substituted m-Bz monomer via ring-opening reaction.12488
Figure III - 5. Possible polymerization reactions sites in order the most to the least
predominant: 1 ortho, 2 para, 3 meta.120 ............................................................................................................. 88
Figure III - 6. Chemical structures of the Bz monomers used for the elaboration of Bz/CNT
nanocomposites.143 – M1: Bisphenol A/aniline based Bz monomer and M2: 1,4-phenylene
diamine/phenol based Bz monomer. .................................................................................................................... 89
Figure III - 7. Representative SEM images of a) pristine kaolin and b) 10 wt% kaolin/EDBz. .... 90
Figure III - 8. Chemical structure and thermal properties of Bz monomers containing carboxylic
groups.158 .......................................................................................................................................................................... 92
Figure III - 9. Chemical structures of Class A and Class B di-Bz monomers. ....................................... 93
Figure III - 10. Chemical structure of Class B di-Bz monomer. ................................................................. 94
Figure III - 11. Synthesis of di-Bz monomers bearing maleimide functional groups. 167 ............... 98
Figure III - 12. Example of naturally occurring phenolic derivatives used for the synthesis of
bio-based Bz monomers. .......................................................................................................................................... 100
Figure III - 13. Schematization of the participation of the aldehyde group in the ring opening
polymerization of the para hydroxyl benzaldehyde Bz monomers.182 ................................................. 103
Figure III - 14. Crosslinking of vanillin-based di-Bz monomers.181 ....................................................... 103
Figure III - 15. Chemical structure of lignin-derivative compounds: coumaric acid (CA), ferulic
acid (FE), and phloretic acid (PA). ........................................................................................................................ 105
Figure III - 16. Available positions for ring opening polymerization of eugenol-based Bz
monomer. ........................................................................................................................................................................ 107
Figure III - 17. Elaboration of crosslinked materials from eugenol-based Bz monomers by
copolymerization between allyl group and bismaleimides.187 ................................................................. 107
Figure III - 18. Chemical structures of a) umbeliferone and b) 4-methylumbeliferone coumarin
compounds. .................................................................................................................................................................... 109
Figure III - 19. Chemical structure of urushiol. ............................................................................................. 113
Figure III - 20. Available positions for ring opening polymerization of urushiol-based Bz
monomer. ........................................................................................................................................................................ 114
Figure III - 21. Synthesis di-Bz asymmetric monomer by reaction between aminophenol and
hydrobenzaldehyde and butylamine (u-butyl-Bz) or hexylamine (u-hexyl-Bz).201 ......................... 116
Figure III - 22. Synthesis of blends of di-eugenol, di-cardanol and asymmetric eugenol/cardanol
di Bz monomers. 202 .................................................................................................................................................... 117
Figure III - 23. Synthesis of symmetric Bz monomers from various phenolic compounds like
phenol, vanillin or cardanol. ................................................................................................................................... 118
Figure III - 24. 1H NMR spectrum (in CDCl3) of di-phenol benzoxazine monomer. ....................... 119
Figure III - 25. 1H NMR spectrum (in CDCl3) of di-vanillin benzoxazine monomer. ...................... 120
17
Figure III - 26. 1H NMR spectrum (in CDCl3) of di-cardanol benzoxazine monomer. .................... 122
Figure III - 27. MALDI-TOF/MS spectrum of di-phenol benzoxazine monomer. ............................ 124
Figure III - 28. HRMS spectrum of di-vanillin benzoxazine monomer. ............................................... 125
Figure III - 29. HRMS analysis of di-vanillin Bz monomer a) Zoom of the experimental product
peaks b) Theoretical mass of the expected product. .................................................................................... 125
Figure III - 30. HRMS spectrum of di-cardanol benzoxazine monomer. ............................................. 126
Figure III - 31. HRMS analysis of di-cardanol Bz monomer a) Zoom of the experimental product
peaks b) Theoretical mass of the expected product. .................................................................................... 126
Figure III - 32. MS/MS analysis of di-cardanol Bz monomer. .................................................................. 127
Figure III - 33. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of di-phenol monomer. . 128
Figure III - 34. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of di-vanillin Bz monomer.
............................................................................................................................................................................................. 129
Figure III - 35. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of the di-cardanol
benzoxazine monomer. ............................................................................................................................................. 130
Figure III - 36. Isothermal rheology monitoring of di-phenol Bz monomer at 190 °C – empty
markers: storage modulus G’; filled markers: loss modulus G’’. .............................................................. 131
Figure III - 37. Isothermal rheology monitoring of di-cardanol Bz monomer at 190 °C – empty
markers: storage modulus G’; filled markers: loss modulus G’’. .............................................................. 131
Figure III - 38. Synthesis of the asymmetric Vani-Card Bz monomer from cardanol and vanillin.
............................................................................................................................................................................................. 133
Figure III - 39. 1H NMR spectrum (in CDCl3) of Vani-Card benzoxazine monomer. ....................... 134
Figure III - 40. HRMS analysis of Vani-Card Bz monomer a) Zoom of the experimental product
peaks b) Theoretical mass of the expected product. .................................................................................... 137
Figure III - 41. HRMS spectrum of Vani-Card benzoxazine monomer. ................................................ 137
Figure III - 42. DSC thermograms (N2, 20 K/min) of a) di-vanillin, b) Vani-Card Bz monomers
and c) di-cardanol Bz monomer. ........................................................................................................................... 138
Figure III - 43. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of the Vani-Card Bz
monomer. ........................................................................................................................................................................ 139
Figure III - 44. Isothermal rheology monitoring of Vani-Card (circular markers) and di-cardanol
(triangular markers) benzoxazines at 190°C – empty markers: storage modulus G’; filled
markers: loss modulus G’’. ....................................................................................................................................... 140
Figure III - 45. DMA thermograms of poly(di-cardanol), poly(di-phenol) and poly(Vani-Card).
............................................................................................................................................................................................. 142
Figure III - 46. TGA (air atmosphere, 20K/min) thermograms of a) di-cardanol, b) di-phenol
and c) Vani-Card PBz materials. ............................................................................................................................ 143
18
Figure IV - 1. Chemical structure of diglycidyl ether of cardanol (CDGE) – commercially
available NC514 - from Cardolite Corporation................................................................................................ 146
Figure IV - 2. Friedel-Crafts alkylation of phenol with cardanol (ideal reaction pathway). ....... 147
Figure IV - 3. Chemical structure of diglycidyl ether of cardanol determined by 1H NMR
analysis.213 ...................................................................................................................................................................... 148
Figure IV - 4. Chemical structure of CDGE obtained from NMR and SEC analysis.213 .................... 148
Figure IV - 5. Additional chemical compounds composing CDGE determined by MALDI-MS
analysis a) epoxidized cardanol bearing an additional phenol moiety, b) epoxidized cardanol
containing both an epoxidated and a native phenol on its side chain, c) epoxidized cardanol
linked to a native cardanol, d) two epoxidized cardanol linked by a native phenol.204 ................. 149
Figure IV - 6. CDGE cross-linking agents a) isophorone diamine and b) Jeffamine D400. .......... 150
Figure IV - 7. Chemical structure of 1,2-diaminocyclohexane (DAC) cross-linking agent. .......... 151
Figure IV - 8. Synthesis of Pbz/epoxy co-networks.217 ............................................................................... 152
Figure IV - 9. Reaction between epoxy and primary and secondary amine functions. ................. 153
Figure IV - 10. Reaction scheme of opening the oxazine ring via an amine nucleophilic attack.229
............................................................................................................................................................................................. 154
Figure IV - 11. Sequential synthesis of IPN. .................................................................................................... 155
Figure IV - 12. In-situ IPN synthesis. .................................................................................................................. 155
Figure IV - 13. Nucleation and growth mechanism. .................................................................................... 156
Figure IV - 14. Gyroïdal structure. ...................................................................................................................... 156
Figure IV - 15. a) Expected reactions during the IPN sequential in-situ synthesis, b) in-situ
sequential synthesis of a poly(CDGE)/poly(Bz) IPN material. ................................................................. 158
Figure IV - 16. Chemical structure of the EDBz model Bz monomer. ................................................... 159
Figure IV - 17. Curing conditions of CDGE with various diamine compounds monitored by DSC
analysis (N2, 20 K/min), compared to the curing conditions of the EDBz monomer (Dashed
curve, (N2, 20 K/min)). .............................................................................................................................................. 160
Figure IV - 18. Curing conditions of various systems a) CDGE with IPD, b) EDBz and c) 60/40
CDGE/EDBz with IPD monitored by DSC analysis (N2, 20 K/min). ........................................................ 162
Figure IV - 19. Curing conditions of CDGE/EDBz (60/40 % wt) systems. ......................................... 163
Figure IV - 20. DSC analysis (N2, 20 K/min) of the poly(CDGE) material (without EDBz) after the
first curing step of 16 h at 100 °C. ........................................................................................................................ 164
Figure IV - 21. DSC analysis (N2, 20 K/min) of the poly(CDGE)/EDBz (60/40) system after the
first curing step of 16 h at 100 °C, and compared to neat poly(CDGE) after 16 h at 100 °C. ....... 165
Figure IV - 22. DSC analysis (N2, 20 K/min) of the poly(CDGE)/poly(EDBz) (60/40) material
after the full curing program (1 h at 160 °C, 2h at 180 °C, 2h at 200 °C and 30 min at 220 °C). 166
19
Figure IV - 23. Evolution of the storage modulus E’ of poly(CDGE)/poly(EDBz) IPNs (80/20,
70/30, 60/40, 50/50, 40/60, 30/70 and 20/80) as a function of temperature, obtained by DMA
(Tension mode with 0.05 % strain, 1 Hz and 3 °C/min). ............................................................................ 167
Figure IV - 24. Evolution of the storage modulus E’ and tanδ of poly(CDGE)/poly(EDBz) IPNs
(80/20, 70/30 and 60/40) as a function of temperature, obtained by DMA (tension mode with
0.05% strain, 1Hz and 3°C/min). .......................................................................................................................... 168
Figure IV - 25. Evolution of the tanδ of poly(CDGE)/poly(EDBz) IPNs (50/50, 40/60, 30/70 and
20/80) as a function of temperature, obtained by DMA (tension mode with 0.05% strain, 1Hz
and 3°C/min). ................................................................................................................................................................ 169
Figure IV - 26. Shear modulus of poly(CDGE)/poly(EDBz) IPN materials versus EDBz volume
fraction compared with modulus-composition models. ............................................................................. 172
Figure IV - 27. DSC thermograms of poly(CDGE)/poly(EDBz) IPNs (80/20, 70/30, 60/40,
50/50, 40/60, 30/70 and 20/80) and poly(CDGE) and poly(EDBz), during the heating of
swollen materials (N2, 5 K/min). .......................................................................................................................... 173
20
List of Tables
Table I - 1. Composition of the phenolic components in natural and technical CNSL.11 ................. 27
Table I - 2. Composition of the abundances of the constituents of cardanol by various
techniques.10 .................................................................................................................................................................... 28
Table I - 3. Percentage retention of the physical properties after ageing of the PVC compounds
dioctyl phthalate (DOP), Cl-cardanol, Cl-cardanol acetate, Cl-cardanol methyl ether.39 ................. 31
Table I - 4. Physico-chemical properties of the reactive surfactants compared to the properties
of standard non-reactive sodium dodecyl sulfonate anionic surfactant. ............................................... 35
Table I - 5. Isolated product yields (%) of phase transfer catalysed reactions.49 .............................. 36
Table I - 6. Properties of phenalkamines synthetized from cardanol, formaldehyde and
isophorone diamine.56 ................................................................................................................................................. 39
Table I - 7. DTA measurements describing antioxidants effects of various antioxidants in MLO
under air atmosphere.59 (Ti: initial thermal degradation temperature, Tmax: degradation
temperature.) .................................................................................................................................................................. 41
Table I - 8. DTA measurements describing antioxidants effects of various antioxidants in MLO
under air atmosphere.60 (Ti: initial thermal degradation temperature, Tmax: degradation
temperature.) .................................................................................................................................................................. 42
Table I - 9. Inhibition rate constants (kinh) obtained by studying the AIBN initiated autoxidation
of styrene at 30 °C in homogeneous solution using chlorobenzene (PhCl) as a solvent, or in a
two-phases water/styrene system.62 .................................................................................................................... 42
Table I - 10. Thermal of CAP1 and CAP2 based PU materials.77 (T10% is the temperature at 10
wt% weight loss and Tmax is the temperature at maximum rate weight loss). .................................... 48
Table II - 1. Example of fillers for the elaboration of nanocomposites.83 ............................................. 54
Table II - 2. CardS1 experimental and theoretical integrations. ............................................................... 66
Table II - 3. CardS2 experimental and theoretical integrations. ............................................................... 67
Table II - 4. CardS3 experimental and theoretical integrations. ............................................................... 68
Table III - 1. Polymerization temperatures of (cardanol/aniline) PBz cured with 1 mol%
catalyst.156 ......................................................................................................................................................................... 91
Table III - 2. Thermal properties Bz materials from reaction between m1 and carboxylic-
containing Bz co-monomers m2, m3, and m4. 158 ............................................................................................ 93
Table III - 3. Reaction times of synthesis of Bz monomers in CHCl3 at reflux with increasing
diamine chain length.162 .............................................................................................................................................. 95
21
Table III - 4. Melting point (Tm) and polymerization temperature (Tp) of model aromatic-di-Bz
monomers and Tg of their corresponding aromatic-PBz materials. ......................................................... 96
Table III - 5. Thermal properties of aliphatic- di-Bz monomers, synthetized from various chain
length linear diamines and phenol, and Tg of their corresponding aliphatic-PBz materials. ........ 97
Table III - 6. Thermal properties of vanillin-based Bz monomers, synthetized from mono-
functional amines or diamines, and Tg and T5% of their corresponding PBz materials. ................. 102
Table III - 7. Thermal properties of guaïacol-based Bz monomers, synthetized from mono-
functional amines or diamines, and Tg and T5% of their corresponding PBz materials. ................. 104
Table III - 8. Thermal properties of lignin-derivative-based Bz monomers, synthetized from
mono-functional amines or diamines, and Tg and T5% of their corresponding PBz materials. ... 106
Table III - 9. Thermal properties of eugenol-based Bz monomers, synthetized from mono-
functional amines or diamines, and Tg and T5% of their corresponding PBz materials. ................. 109
Table III - 10. Thermal properties of coumarin-based Bz monomers, synthetized from mono-
functional amines or diamines, and Tg and T5% of their corresponding PBz materials. ................. 110
Table III - 11. Thermal properties of cardanol-based Bz monomers, synthetized from mono-
functional amines or diamines, and Tg and T5% of their corresponding PBz materials. ................. 112
Table III - 12. Thermal properties of urushiol-based Bz monomers, synthetized from amines or
diamines, and Tg and T5% of their corresponding PBz materials. ............................................................ 114
Table III - 13. Assignments of the 1H NMR peaks of the di-phenol benzoxazine monomer and
their theoretical and experimental integrations. ........................................................................................... 120
Table III - 14. Assignments of the 1H NMR peaks of the di-vanillin benzoxazine monomer and
their theoretical and experimental integrations. ........................................................................................... 121
Table III - 15. Assignments of the 1H NMR peaks of the di-cardanol benzoxazine monomer and
their theoretical and experimental integrations. ........................................................................................... 123
Table III - 16. Assignments of the 1H NMR peaks of the asymmetric Vani-Card Bz monomer and
their theoretical and experimental integrations. ........................................................................................... 136
Table III - 17. Thermal properties of symmetric and asymmetric di-benzoxazine monomers.
Values are obtained from DSC (a), TGA (b) and rheology (c) analyses. ................................................ 140
Table III - 18. Thermal properties of symmetric and asymmetric PBz materials. Values are
obtained from DMA (a), and TGA (b) analyses. ............................................................................................... 143
Table IV - 1. Thermomechanical properties of CDGE cured with IPD or Jeff400, compared to
BADGE/IPD network.213 ............................................................................................................................................ 150
22
General Introduction and Context
In the recent years, the interest of the researchers, both from the academy and industry, in the
chemistry of renewable resources and related materials has considerably grown. Indeed, until
recently, the largest part of the resources used for the production of commodity materials is
mainly petroleum-based compounds. Furthermore, the world production of plastic materials is
constantly increasing, reaching in 2014 a production of 311 million tons of plastic, using 8 % of
the global petroleum annual world production.1 The production of petroleum-based plastic
materials concerns a wide range of applications such as packaging (39.5 %), building and
construction (20.1 %), automotive (8.6 %), electrical and electronics (5.7 %) or agriculture (3-4
%). Various sectors such as consumer and household appliances, furnitures, sports, or health and
safety constitute 22.7 % of the global demand. However, the depletion of fossil resources,
combined to their increasing prices and the growing environmental concerns, led to huge demand
in the development of new bio-based precursors. Nowadays, bioplastics are representing a
minority of the world plastic production, less than 1 % of the global plastic production.2 In 2013
the bioplastic production amounted only around 1.6 million tons. Nevertheless, the demand is
rising, and by 2018 the production capacity is expected to increase to 6.7 million tons, leading to
more and more sophisticated bioplastic materials (Figure 1).
Figure 1. Global production capacities of bioplastics (In 2013 and forecast for 2018).2
23
In consequence, numerous researchers focused in the past few years on the use of naturally
occurring building-blocks for the synthesis of monomers and polymeric materials. Up to now, the
natural resources used to this aim are predominantly agricultural crops such as corn, cereals,
sugar beets and sugar cane (first generation feedstock); most of them competing with food value
chain. Nevertheless, the bioplastic industry favours now the natural resources provenance rather
towards non-food crops and non-edible by products (second and third generation feedstock),
among others, cellulose. Indeed, a large amount of cellulosic by-products are produced by the
growing of crops such as straw, corn stover or bagasse which could be recovered. Other
renewable materials such as wood, proteins, lignin, tannins, starch, vegetables oils or even animal
resources such as chitin, are also widely studied and used. However, many of these naturally
occurring resources exhibit important drawbacks such as low purity and high molar masses,
reducing their industrial development. The depolymerisation of lignin for example also remains
very challenging, limiting its exploitation as source of chemical building blocks.3 Among the
possible raw renewable materials available for the development of new bio-based materials,
cardanol is gaining considerable interest as a natural source of phenol and a versatile building
block.4 Cardanol is produced from Cashew Nutshell Liquid (CNSL), and is an economical and
abundant non-edible agricultural annually renewable resource used in many applications in
research and industry.5 Indeed, in 2013, the world production of cashew nuts in shell was
estimated to 4.4 million tons.6 Beside the sustainability, availlabatility and the advantageous price
of raw cardanol compound, its particular aromatic structure makes it an interesting and
promising natural alternative to petrochemical derived phenols. Indeed, due to similar reactivity
to a phenol compound and through various chemical modifications on its three main availlable
reactive sites, a wide range of molecules can be designed with wide application range such as
surfactants, plasticizers or polymer precursors. The raw cardanol compound was already
intesively studied, and a state of the art of the possible chemical modifications and their
applications will be described in a first introductive chapter. The following chapters are them
highlighting various chemical modification strategies we applied to cardanol for the elaboration,
or the reinforcement of polymeric materials as tentative ways to find new high value applications
of these raw biobased building blocks.
First of all, we report in Chapter II the synthesis of a set of novel cationic surfactants prepared
from cardanol. The synthetized ammonium cardanol-based surfactants exhibited interesting
properties. They were thus herein applied for the organomodification of Montmorillonite (MMT),
a clay mineral widely used as filler in polymer materials for its reinforcing, thermal and gas
barrier properties. Indeed, it is well established that the chemical structure of surfactants used
for the organomodification of clay minerals plays an important role on the clay exfoliation during
24
the elaboration of nanocomposite materials. The compatibilization of clay mineral and polymer
material may be enhanced by the incorporation of reactive surfactants capable to covalently graft
to monomers and polymer chains. It will be evidenced that cardanol-based surfactants act as
efficient compatibilizers of MMT within epoxy polymer. Furthermore, it will be demonstrated that
the reactivity of the synthetized surfactants plays a particular role on the clay exfoliation
mechanism within an epoxy matrix. Interestingly, different (nano)composite structures were
observed depending on the reactivity of the surfactants.
As highlighted before, cardanol is a naturally occurring phenolic compound that has recently
attracted attention for the synthesis of benzoxazine monomers. Undergoing the efforts to
promote the development of bio-based benzoxazine thermosets, we explore in Chapter III a new
strategy for the elaboration of bio-based and processable Bz-materials. In particular, Bz
monomers from cardanol alone or in conjunction with some lignin derivatives – like vanillin –
were studied. A versatile synthesis of asymmetric di-benzoxazine monomers from naturally
occurring phenolic compounds cardanol and vanillin was developed. By taking advantage of the
low reactivity of cardanol, a mono-substituted cardanol-based benzoxazine monomer was
prepared and further coupled with vanillin to yield vanillin-cardanol di-benzoxazines. The
asymmetric monomer presents the great advantage of displaying a low melting temperature and
thus a wide processing window, facilitating its processing (melting and shaping). Furthermore, a
moderate gelation time was observed as well as high Tg for the polymerized material. Such
strategy constitutes an efficient and versatile route for an easy elaboration of bio-based
monocomponent thermosets.
Finally, in the last chapter we envision the substitution of Bisphenol A - a well-known endocrine
disruptor - in coatings, by using diglycidyl ether of cardanol (CDGE). Because of its weak
properties (Tg, storage modulus, water repellence), coatings prepared with CDGE need to be
reinforced. In particular, we focused on a macromolecular reinforcement by the elaboration of
interpenetrating polymer networks of CDGE and polybenzoxazine (PBz). Indeed, CDGE thermoset
materials display poor thermo-mechanical properties, whereas PBz resins are well-known for
being high performance materials. In spite of the possible co-crosslinking between cardanol
diglycidyl ether and benzoxazine monomers, leading to polymer co-networks, we found the
appropriated experimental conditions to only tangle the two polymer networks without chemical
links between the two networks. The elaboration and the properties of these interpenetrating
polymer networks are reported in this last chapter.
25
Chapter I: Introduction
1 Cashew nutshell liquid: extraction and composition
The cashew nut industry is largely present in countries of tropical regions, such as India, Brazil,
and Viet Nam. The global world production of cashew nut crops was estimated around 4 million
tons in 2012 (Food and Agriculture Organisation (FAO)), mainly located in Vietnam (1.2000.00
tonnes/year) followed by Nigeria, India, etc. (Figure I - 1 (FAO STAT data, 2013)).6
Figure I - 1. Main cashew nut producing countries in 2012.
The cashew nut stems from the cashew apple fruit (Figure I – 2) of the cashew tree Anacardium
occidentale L., native species from Brazil. The cashew nut is the seed of the cashew apple. Both
cashew apple and nut are comestible and widely consumed products.
Figure I - 2. Representation of cashew apples.
Cashew nuts are commercialised without their shell due to a highly vesicant substance it contains
at a raw state: the cashew nutshell liquid (CNSL) is considered as an important by-product of this
industry.
26
Extracted from the soft honeycomb structure of cashew nutshells - mesocarp spongy - (Figure I
-3) during the shelling process of cashew nuts, CNSL is an economical and abundant non-edible
agricultural renewable resource used in many applications in research and industry. CNSL
constitutes about 20-25% of the weight of the cashew nut. It is usually used in its technical state
in various industrial applications such as brake linings, surface coatings, paints, varnishes,
lacquers, adhesives or laminates.5
Figure I - 3. Cross section of a cashew nut and nutshell.
CNSL is the most known source of phenolic lipids in plants. The oil is mainly composed of four
phenolic constituents – hydroxyalk(en)ylbenzene homologs namely anacardic acid, cardanol,
cardol and 2-methyl cardol - substituted in meta position by an unsaturated C15 alkyl chain
(Figure I - 4). Unlikely to other phenolic lipids found for instance in cereals, the chain length of
these constituents is not varying. However, each of them is composed of a mixture of four
components differing by their unsaturation degree, from saturated to tetraenoic one.7
Figure I - 4. Chemical structure of CNSL components a) anacardic acid, b) cardanol, c) cardol
and d) 2-methylcardol.
Different oil compositions, i.e. the abundance of the four constituents and their respective
unsaturated forms, are obtained depending on the extraction process. These processes can be
roughly classified in two types: extractions in cold/room temperature conditions and extractions
in heating conditions.
27
Naturally occurring CNSL - obtained by cold-pressing or solvent-extraction –contains mainly four
phenolic constituents: anacardic acid (70-80%), cardol (15-20%), cardanol (1-7%) and traces of
2-methyl cardol (1-4%).
Technical CNSL (i.e. commercial CNSL) is extracted by roasting the nutshells and is mainly
constituted of cardanol (60-85%), cardol (4-20%), and traces of 2-methylcardol (1-5%). It barely
contains anacardic acid which is converted into cardanol through thermal decarboxylation during
the roasting and refining processes (Figure I - 5). Oligomeric or polymeric materials (7-20%)
were also found to be present mainly in technical CNSL.8,9
Figure I - 5. Anacardic acid decarboxylation.
The composition of the different grades of the obtained oils by these extraction processes are
gathered in Table I - 1.10
CNSL type CNSL phenolic components (%)
Anacardic acid (%) Cardanol (%) Cardol (%) 2-methylcardol (%)
Natural CNSL 74.1-77.4 1.2-9.2 15.0-20.1 1.7-2.6
Technical CNSL 1.0-1.8 74.7-84.7 11.6-18.9 2.2-5.2
Table I - 1. Composition of the phenolic components in natural and technical CNSL.11
2 Extraction of cardanol from CNSL and reactivity
The industrial grade of cardanol oil recovered from CNSL, may reach 90% of cardanol content
and a smaller percentage of cardol and methylcardol.12, 13 As above mentioned, cardanol is a
mixture of four phenolic molecules differing by their degree of unsaturation of their alkyl side
chain and the determination of their relative abundance has been the subject of many researches
through various methods. Table I - 2 summarizes the abundances of the different unsaturations
as a function of the employed characterization technique. It can be observed that depending on
the characterization technique and on the origin of the product the unsaturation abundances can
slightly vary.
28
Cardanol side chain
unsaturations (%)
Saturated
(%)
Monoene (%) Diene (%) Triene (%)
Employed technique
Molecular distillation - 60.0 10.0 30.6
Silver ion chromatography 5.4 48.5 16.8 29.3
TLC-GLC 2.7 29.5 16.6 51.2
TLC-mass spectroscopy 2.0 31.3 15.2 51.5
Table I - 2. Composition of the abundances of the constituents of cardanol by various
techniques.10
Cardanol was thus found to display an average of 1.5 unsaturations, with a majority of tri-
unsaturated compound (40-50%), followed by the mono-unsaturated compound (30-35%), the
di-unsaturated compound (15-20%), and very few saturated compound (1-4%) (Figure I – 6).
Figure I - 6. Average compositions of the cardanol alkyl side chain.
Cardanol displays a similar reactivity than phenol, and is thus a promising renewable substituent
to petroleum-based phenolic compounds. Indeed, cardanol has three different sites available for
panoply of chemical reactions (Figure I – 7).
Figure I - 7. Representation of the possible chemical modifications on the three reactive sites of
cardanol.
29
The reactive hydroxyl group on cardanol allows chemical reactions such as esterification,14
allylation,15, 16 epoxidation,17-25 or ethoxylation.26, 27 Structural changes may also occurred by
reacting the aromatic ring, for example through condensation,28 nitration,29 sulfonation,30,31
bromination,32 and hydrogenation.33 Furthermore, cardanol can also undergo chemical
modifications on the C15 alkyl side chain. Indeed, the side chain unsaturations enable reactions
such as hydrogenation,33 hydrosilylation,34 epoxidation,17, 18 phenolation,35 or metathesis
reactions.36
Consequently, cardanol is used in a wide range of applications (plasticizers, surfactants, curing
agents, antioxidants), depending on its chemical modification, as described in the following sub-
chapter. In the study described in the Chapter II, we took advantage of the amphiphilic chemical
structure of cardanol to synthetize ammonium surfactant by reaction on the phenolic hydroxyl
function (Figure I – 8a). The synthesis of cardanol-based benzoxazine monomers highlighted in
Chapter III occurred also by reaction on the cardanol hydroxyl group, coupled to a reaction on the
aromatic ring on cardanol (Figure I – 8b). Finally the synthesis of a cardanol diglycidyl ether
compound studied in the Chapter IV resulted from modification on both hydroxyl phenolic group
and alkyl side chain unsaturations of cardanol (Figure I – 8c).
Figure I - 8. Fine chemicals and functional molecules from cardanol.
30
3 Cardanol based chemicals and functional molecules
Among fine chemicals and functional molecules from cardanol reported in the literature, there
are plasticizers, surfactants, curing agents or antioxidants.
3.1 Plasticizers and reactive diluents
The incorporation of a plasticizer molecule within a polymeric material increases its flexibility
and processability. A plasticizing compound is usually a low molecular weight molecule with both
suitable polar and non-polar entities. Indeed a plasticizer molecule is able to penetrate within a
polymeric matrix through hydrophobic compatibility and to establish polar attractive forces with
the polymeric matrix chains reducing thus the cohesive forces between the polymer chains
(Figure I – 9).
Figure I - 9. Schematic representation of polymer matrix a) plasticizer-free and b) in presence
of a plasticizer.
Due to its chemical and physical properties, cardanol is a promising bio-based plasticizer. The
C15 alkyl chain represents the hydrophobic entity of cardanol, while the hydroxyl group can be
chemically modified into a hydrophilic group endowing plasticizing properties to the molecule.
Hence, with the actual concern of replacing the commonly used phthalate-based plasticizers
because of toxic release,37 both raw and chemically modified cardanol compounds are intensively
used as plasticizer.
For instance neat cardanol has been used as plasticizer for Poly(methyl methacrylate) (PMMA)
as reported by Prabhakaran et al.38. The rheological properties were influenced by the addition
of cardanol to PMMA. The viscosity decreased from 6.4 Pa.s to 1.5 Pa.s with increasing the weight
31
ratio of cardanol/PMMA from 0.33 to 1. Furthermore, the plasticizing effect of cardanol was
evidenced by the decrease of the Tg of PMMA-cardanol blends from 48 °C to -12 °C with the
addition of 50 wt % of cardanol in PMMA.
Chlorinated cardanol as well as its chlorinated acetyl and methoxy derivatives were tested for the
partial replacement of dioctyl phthalate (DOP) in polyvinyl chloride (PVC) leading to an
improvement of the properties of the material as resumed in Table I – 3.39 The DOP was added
to the PVC compound in a 50/50 ratio to the synthetized cardanol-based plasticizers.
Plasticizer
DOP
DOP/Cl-
cardanol
DOP/Cl-
cardanol
acetate
DOP/Cl-
cardanol methyl
ether
Percentage
retention
Physical
properties
(%)
Hardness 105.4 108.1 109.0 94.36
Tensile
strength
122.8 100.6 101.2 114.8
Modulus 143.4 111.7 126.2 138.2
Elongation 90.9 83.3 92.9 92.3
Table I - 3. Percentage retention of the physical properties after ageing of the PVC compounds
dioctyl phthalate (DOP), Cl-cardanol, Cl-cardanol acetate, Cl-cardanol methyl ether.39
The chlorinated cardanol methyl ether (Cl-cardanol methyl ether) appears to be a good plasticizer
for PVC with comparable performances to DOP, particularly thermal once. Similarly, acetyl
cardanol derivatives were evaluated as plasticizer in PVC.14, 40, 41 Thermal and mechanical
properties of the resulting PVC-based materials were comparable to those of PVC plasticized with
di-ethyl-hexyl-phtalate (DEHP) or DOP lonely.
However, a well-known drawback of plasticizers is their migration from the bulk to the surface
of the host polymer matrix. To prevent this phenomenon plasticizers are generally modified with
a reactive function towards the polymer matrix (reactive plasticizer). Furthermore, the addition
of a reactive plasticizer to high viscosity epoxy is known to reduce the viscosity and facilitate the
materials processing. In the case of cardanol, the most common reactive cardanol-based
plasticizer used to prevent its migration is obtained from the reaction of cardanol with
epichloridrin in basic conditions. This cardanol derivative is commercially available under the
Trade mark NC-513 (Cardolite) (Figure I - 10).42
32
Figure I - 10. Chemical structure of mono-epoxidized cardanol NC-513 from Cardolite.
Cardolite finds applications in solvent free epoxy systems used in protective, industrial, and floor
coatings. The reactivity of this mono-epoxy cardanol has been enhanced by the epoxidation of its
side chain unsaturation to form cardanol poly-epoxy derivative (Figure I - 11). This compound
was then used as reactive diluent for a cardanol-based epoxy.18 The viscosity of a cardanol-based
epoxy decreased significantly from 4780 mPa.s to 2150 mPa.s with the addition of cardanol poly-
epoxy derivative from 10 to 20 %.
Figure I - 11. Chemical structures of cardanol polyepoxy derivatives plasticizers.18
3.2 Surfactants
Surfactants are amphiphilic molecules constituted of a hydrophobic part (the tail) and a
hydrophilic group (the head). They are largely used as detergents, wetting and/or foaming
agents, emulsifiers or dispersants due to their ability to lower the surface tension of a liquid,
between two liquids or between a liquid and a solid.43 Surfactants are classified into four classes
based on the nature of the hydrophilic group (Figure I -12).
Petroleum-stemmed linear alkyl benzenes are the most commonly used reactants for the
synthesis of surfactants. A sustainable alternative would be the synthesis of cardanol-based
surfactants as it could be expected from its appropriate chemical structure. Even though
unmodified cardanol cannot be considered as surfactant but its chemical structure and inherent
amphiphilic properties are ideal for the synthesis of bio-based surfactants. Indeed the C15 alkyl
chain represents the hydrophobic part while the aromatic ring bearing a hydroxyl group
represents the slightly hydrophilic part. The amphiphilic properties of cardanol can be
accentuated by chemical modifications of the phenolic hydroxyl group, obtaining thus cardanol-
33
based surfactants. Through numerous possible chemical modifications of its phenolic hydroxyl
function, various types of surfactants were synthetized from cardanol such as anionic, non-ionic
or cationic surfactants.
Figure I - 12. Schematic representation of the various types of surfactants a) cationic, b)
anionic, c) non-ionic and d) zwitterionic.
3.2.1 Anionic surfactants
Anionic surfactants are negatively charged and have a pronounced hydrophilic character. They
are usually used as wetting or foaming agents in the diverse industries. Anionic surfactants are
the most developed type of cardanol-based surfactants. Cardanol-based sulfonate surfactants are
synthetized from different synthesis pathways. Cardanol sulfonation can be achieved for example
by reaction with fuming sulphuric acid (Figure I -13).30, 31 Sulfonate cardanol surfactant (SC) was
found to have comparable detergent properties to traditional dodecylbenzene sulfonate (DDBS)
surfactant, and can thus be considered as a good alternative. Indeed, the values obtained for
cardanol sulfonate surfactants were very close to those for commercial DDBS when comparing
surface tensions (obtained minimum surface tension = 28 mN/m and 32.25 mN/m for SC (15 %
w/v) and DDBS (15 % w/v) surfactants respectively) and critical micelle concentrations (CMC =
0.372 mol/L and 0.435 mol/L for SC and DDBS surfactants respectively).
34
Figure I - 13. Synthesis of cardanol sulfonate surfactants.30
A sulfonated cardanol-based surfactant was synthetized through diazotation coupling reaction
between cardanol and sulfonic acid diazonium salt (Figure I - 14).44 This surfactant generates
stable emulsions of aniline in water. The corresponding polymer, polyaniline (PANI), is a versatile
conducting polymer in oxidized state (component of organic light emitting devices or organic
photovoltaic devices). As PANI is positively charged it requires counter ion, called dopant, to
ensure electroneutrality. The molecular structure of this cardanol-based dopant allows the
preparation of conducting highly ordered and water soluble PANI nanofibers. Moreover, the
cardanol-based dopant displays free hydroxyl phenolic functionalities, allowing the possibility to
fine-tune the PANI material.
Figure I - 14. Synthesis of cardanol diazonium sulfonate surfactant.44
Anionic type carboxylate surfactants can also be synthetized by modification of the phenolic
hydroxyl function of cardanol (Figure I - 15).45 They were shown to lower the surface tension
and to produce microemulsions in mixture with sodium dodecyl sulfate. A CMC of 8.3x10-4 mol/L
with a corresponding surface tension of 29.16 mN/m was reported.
Figure I - 15. Chemical structure of cardanol carbonate surfactant.45
Surfactants may also bear reactive functions and could thus be able to take part in polymerization
reactions. These reactive-surfactants known as “surfmers” can be used in order to improve the
final material properties.46 Sulfonated acrylate cardanol surfmers (Figure I - 16) are obtained by
35
reaction between different cardanol acrylates and chlorosulfonic acid, and their properties were
compared with standard non-reactive sodium dodecyl sulfonate anionic surfactants (SDS) (Table
I - 4).47
Figure I - 16. Chemical structure of sulfonated acrylate cardanol surfactants a) sulfonated-3-
pentadecyl phenyl acrylate and b) sodium-2-acryloxy ethan-1-oxy(3-pentedecyl) benzene
sulfonate.47
The CMC of the reactive surfactants were reported to be much lower than the conventional SDS
surfactant. Nevertheless, no evaluation of the influence of the reactive surfactants on materials
elaboration were reported by Kattimuttathu et al..47
Compound CMC (mol/L) Surface tension at CMC
(mN/m)
sulfonated-3-pentadecyl
phenyl acrylate
8.7 x 10-5 35.52
sodium-2-acryloxy ethan-
1-oxy(3-pentedecyl)
benzene sulfonate
1.7 x 10-5 31.61
sodium dodecyl sulfonate 0.37 32.25
Table I - 4. Physico-chemical properties of the reactive surfactants compared to the properties
of standard non-reactive sodium dodecyl sulfonate anionic surfactant.
3.2.2 Non-ionic surfactants
Non-ionic surfactants may also be synthetized from cardanol, especially polyethoxylates (Figure
I - 17) that are commonly based on fatty alcohols or alkylphenols.27, 48 Their properties were
characterized by measuring their reduction in surface tension of water by dilute solutions (1 %)
of polyethoxylates, and determine the optimum ethoxylate chain length. It was found that
cardanol polyethoxylate with a C8 ethoxylate chain length showed similar surfactant properties
than traditional t-nonylphenol polyethoxylate.
36
Figure I - 17. Chemical structure of cardanol polyethoxylate surfactants.27, 48
3.2.3 Cationic surfactants
Cationic surfactants can also be synthetized from cardanol. Nevertheless only two studies are
reported in the literature. The synthesis of a quaternary ammonium salt from cardanol was
described.49 The distinctive feature of this compound is the quaternary ammonium located at the
end of the aliphatic chain of cardanol aiming at enhancing the lipophilic character of the
surfactant (Figure I - 18).
Figure I - 18. Chemical structure of cardanol quaternary ammonium salt surfactants.49
Several heterogeneous reactions such as oxidations and Williamson ether synthesis were tested
with cardanol quaternary ammonium salt as phase transfer catalyst. The synthesis yields were
reported similar or even higher to those obtained with a commercially available quaternary
ammonium salt (Aliquat®) (Table I - 5).
Yields (%) of phase transfer catalysed reactions
quaternary
ammonium salt
KMnO4 oxydation NaClO oxydation Williamson ether
synthesis
cardanol based
R = CH3
76 67 76
cardanol based
R = CH2CH3
74 27 98
cardanol based
R = CH2CH2CH3
60 26 84
Aliquat® 64 49 60
Table I - 5. Isolated product yields (%) of phase transfer catalysed reactions.49
37
It is worthy to note that such ammonium salts can find applications for the functionalization of
fillers, like mineral clays. Verge et al.50 reported the synthesis of an ammonium surfactant from
cardanol for the compatibilization and dispersion of sepiolite clay into epoxy thermoset. Mono-
epoxidized cardanol – commercially available NC-513 – was reacted with ethylene diamine and
protonated in acid medium (Figure I - 19). Cardanol-based ammonium surfactants were found
to enhance the compatibility between sepiolite clay and epoxy networks. The studies dealing with
these cationic cardanol-based surfactants are developed in Chap III.
Figure I - 19. Synthesis of cardanol ammonium salt surfactants.51
3.3 Curing agents
With the trend to decrease the carbon footprint of plastics, bio-based curing agents were found
to be particularly appropriate for the preparation of epoxy-based thermosets. More particularly,
phenalkamine is the most commonly developed curing agent from cardanol.52 Phenalkamines are
synthetized by Mannich reaction between cardanol, formaldehyde and diamines (Figure I - 20).
Figure I - 20. Synthesis of cardanol phenalkamine curing agent.52
They advantageously allow the curing of epoxy resin at low temperature (T = 25 °C)53, 54 and lead
to the improvement of the toughness of the resulting resins thanks to the flexible alkyl chain.
Phenalkamines synthetized by reacting cardanol with a mixture of hexamethylenediamine (HDA)
and diethylenetriamine (DETA) (Figure I - 21) were shown to significantly improve the
toughness of Bisphenol A diglycidyl ether (BADGE) epoxy resins in comparison to DETA as curing
agent.55 Additionally a clear decrease of the Tg was observed. Indeed the Tg of the BADGE epoxy
material cured with a phenalkamine synthetized from cardanol and HDA (Tg = 49.5 °C) was found
to be significantly lower than the Tg of a BADGE epoxy material cured with DETA (Tg = 126.7 °C).
38
Figure I - 21. Chemical structure of phenalkamine component from a) hexamethylenediamine
and b) diethylenetriamine.55
The final properties of thermosets cured with phenalkamine compounds depend on the kind of
polyamine used for the synthesis (aromatic or aliphatic) and on the molecular weight of the
resulting phenalkamine, as well as on the amine percentage. The molecular weight of the
resultant phenalkamine depends on the ratio of cardanol, amine and formaldehyde used.
Kathalewar et al. studied the effect of the molecular weight of phenalkamines on the curing and
on the properties of epoxy coatings.56 Phenalkamines of different molecular weight and amine
content – polyphenalkamines - were synthetized from the reaction between cardanol,
formaldehyde and varying concentrations of isophorone diamine (IPD) (Figure I - 22).
Figure I - 22. Synthesis of phenalkamine compounds from cardanol with varying molecular
weight and amine content.56
BADGE epoxy based coatings were then elaborated by curing with the various phenalkamines
and compared with BADGE coatings cured with commercial phenalkamine ARK351. All the
thermosets exhibited single Tg values (Table I – 6).
The Tg values obtained using DSC increased in the order ARK351 < PA1 < PA2 < PA3. An
increasing of the crosslinking density and of the Tg of the thermosets was reported to be in
39
relation with the increase of the phenalkamine molecular weight and amine content. In addition,
it is assumed that the cycloaliphatic moiety in cardanol-based phenalkamines samples was also
responsible for higher Tg than ARK351 sample, which was based on aliphatic polyamine.
Properties PA1 PA2 PA3 ARK351
Mn (g/mol) 498 843 1371 458
Tg (°C) 71 75 88 65
Cross-link
density
(mol/m3)
107 373 784 659
Table I - 6. Properties of phenalkamines synthetized from cardanol, formaldehyde and
isophorone diamine.56
Nevertheless, the high toxicity of formaldehyde, identified as a carcinogenic compound, in
addition to low primary amine functionality of the resulting phenalkamines are main drawbacks
for the use of Mannich-based phenalkamine curing agents. To overcome these shortcomings
Darroman et al.16 proposed the synthesis of a cardanol-based aromatic amine (cardanol
cysteamine) by thiol-ene chemistry (Figure I - 23) and the elaboration of a fully bio-based epoxy
thermoset material.
Figure I - 23. Synthesis of cardanol-based phenalkamine compound by thiol-ene chemistry.16
The researchers focused on synthesizing a poly-amine cross-linking agent. Cardanol was first
allylated by reaction with allyl bromide and the unsaturation of the cardanol alkyl side chain
could be functionalized by thiol-ene chemistry by reaction with hydrochloride cysteamine.
Thermosets materials from cardanol-based diglycidyl ether compound (NC-514), cured with
commercial NX-5454 phenalkamine and with cardanol cysteamine, respectively (Figure I - 24)
were elaborated and their thermo-mechanical properties were compared.
The glass transition temperature values are low for both formulations NC-514/NX-5454 (1/1
ratio) and NC-514/cardanol cysteamine (1/1 ratio) with Tg = 38 °C and 21 °C respectively. The
crosslinking densities of the corresponding networks were also calculated from the DMA storage
modulus at 60 °C above the Tg. The crosslinking density of the NC-514/NX-5454 (ʋe = 280.0
40
mol/m3) is significantly higher than for the NC-514/cardanol cysteamine network (ʋe = 20.3
mol/m3). The higher Tg and crosslinking densities of NC-514/ NX-5454 network can be explained
by the short diethylene triamine (DETA) used for the synthesis of NX-5454 phenalkamine.
Figure I - 24. Chemical structures of a) cardanol-cysteamine, and b) commercial NX-5454
phenalkamine.
3.4 Antioxidant
Antioxidants are used as additives in various polymer-based materials. Indeed, their presence
inhibits the deterioration of the organic material by oxidation under atmospheric conditions
which increases the material lifetime. The most current and efficient additives are ortho and/or
para substituted phenolic compounds. The anti-oxidant effect is depending on the substituents
electronic effects and on their steric hindrance. Indeed, electron-donating effect of the
substituents increases the hydroxyl oxygen electron density, resulting in an efficient radical trap.
An important steric hindrance of the substituents prevents the coupling of phenoxy radicals and
increases their efficiency.57
Figure I - 25. Chemical structures of cardanol-based antioxidants.
41
Cardanol, through its phenolic chemical structure and particularly through the steric hindrance
brought by the alkyl side chain has been reported to be a suitable compound for antioxidant
applications, especially for petroleum products. Nevertheless, the antioxidant activity of non-
modified hydrogenated cardanol and cardol compounds was very low in comparison to
commercial antioxidant compounds such as butyl hydroxyl toluene (BTH).58 In consequence,
various modifications of cardanol were reported (Figure I - 25) attesting of its efficiency as
radical scavenger.
The alkylphenol synthetized by Rios et al.59 (A1, Figure I - 25) by alkylation of hydrogenated
cardanol was reported to reduce the formation of oxidation products in mineral lubricant oil
(MLO). Differential Thermal Analysis (DTA) of mineral lubricant oil with various antioxidants
such as cardanol-based 5-n-pentadecyl-2-tert-butylphenol (A1) and currently used 2,6-di-t-
butyl-4-methylphenol (BHT, an alkylphenol) and IRGANOX® (a diphenyl phosphate) are
summarized in Table I - 7. The higher degradation temperatures were recorded for MLO
modified with the cardanol-based antioxidant, Tmax = 246 °C, justifying its effective antioxidant
properties.
Sample Ti (°C, air) Tmax (°C, air)
MLO 91 225
MLO + 1 % A1 171 246
MLO + 1 % BHT 164 221
MLO + 1 % IRGANOX 166 230
Table I - 7. DTA measurements describing antioxidants effects of various antioxidants in MLO
under air atmosphere.59 (Ti: initial thermal degradation temperature, Tmax: degradation
temperature.)
The antioxidant effect of cardanol-based organophosphate compounds (A2, Figure I - 25) in
mineral lubricant oil (MLO) was also studied.60 The organophosphate antioxidant compound (A2)
was synthetized by alkylation of hydrogenated cardanol, followed by reaction with diethyl
chlorophosphate. Its antioxidant effectiveness was demonstrated by DTA measurements of MLO
with the cardanol-based phosphate compound and compared to MLO with alkylphenol and
diphenyl phosphate antioxidants (Table I - 8).
The antioxidant effectiveness of cardanol-based phosphate compound is proven by the higher
initial thermal degradation temperature (Ti = 156 °C) than for mineral oil without antioxidant (Ti
= 91 °C). Furthermore, its antioxidant effectiveness is comparable to those of current alkylphenols
or diphenyl phophates. The good thermo-oxidative stability of cardanol-based phosphate
compound can be explained by the bulkier substituent on ortho and para positions, increasing
42
the structures conjugation. Further studies on cardanol-based phosphate antioxidants
compounds (A4 and A5, Figure I - 25) reported similar results, and confirmed their efficient
antioxidant action for mineral oils.61
Sample Ti (°C, air) Tmax (°C, air)
MLO 91 226
MLO + 1 % A2 156 204
MLO + 1 % alkylphenol 178 239
MLO + 1 % diphenyl phosphate 152 201
Table I - 8. DTA measurements describing antioxidants effects of various antioxidants in MLO
under air atmosphere.60 (Ti: initial thermal degradation temperature, Tmax: degradation
temperature.)
With the aim of combining the antioxidant properties of hydroxyl 4-thiaflavane compounds and
the amphiphilic property of cardanol, Amorati et al.62 proposed the synthesis of a cardanol-based
4-thiaflavane anti-oxidant (A3, Figure I - 25) by Diels-Alder reaction. The rate constants for the
reaction with peroxyl radicals were measured by studying the autoxidation of styrene
(monitoring of the oxygen consumption) at 30 °C in presence of the synthetized antioxidant
compounds. The cardanol-based 4-thiaflavane antioxidant (A3) appeared very efficient because
it displayed rate constants, for reaction with peroxyl radicals, from 50 to 70 times higher than
hydrogenated cardanol, independently from the medium used to run the measures (Table I - 9).
kinh/105 M-1s-1
Measurement
medium
Styrene/PhCl Styrene/H2O H2O/PhCl
Cardanol 0.1 0.1 1
A3 (R = H) 7.0 5.2 0.7
A3 (R = CH3) 7.0 5.3 0.9
Table I - 9. Inhibition rate constants (kinh) obtained by studying the AIBN initiated autoxidation
of styrene at 30 °C in homogeneous solution using chlorobenzene (PhCl) as a solvent, or in a
two-phases water/styrene system.62
4 Cardanol-based polymers
Due to its particular chemical structure, cardanol is used as a building block for the synthesis of
many different polymer materials such as phenolic or epoxy resins, as well as polybenzoxazines
or polyurethane thermosets. The three available reactive sites on cardanol enable the synthesis
of numerous kinds of cardanol-based polymers. Furthermore, the presence of the C15 alkyl chain
43
endows hydrophobic properties to the material as well as flexibility on account of internal
plasticization.
4.1 Phenolic resins
One of the most considered applications of cardanol is its use as phenolic precursor for novolac
or resole type resin. Indeed, cardanol can undergo condensation with formaldehyde at ortho or
para position of the phenolic ring to form cardanol-formaldehyde (CF) resins (Figure I - 26).63
Figure I - 26. Synthesis of cardanol-based phenolic resin.63
The presence of the alkyl side chain increases hydrophobicity and results in highly flexible
materials with lower mechanical properties than usual phenol-formaldehyde resins. As a
consequence, cardanol-formaldehyde resins are barely used alone, but mainly in blends with
phenol-formaldehyde resins to obtain materials with good toughness.28, 64, 65
Some studies also reported the substitution of formaldehyde by furfural - a bio-based heterocyclic
aldehyde obtained from agricultural waste - and the synthesis of cardanol-furfural resins (Figure
I - 27). The replacement of formaldehyde by furfural promotes the thermal stability of the
phenolic resin. Indeed, according to the TGA results, cardanol-furfural resins display a higher
thermal stability as cardanol-formaldehyde resins. The furfural moiety of cardanol-furfural resins
was shown to be thermally more stable than the methylene bridge of cardanol-formaldehyde
resins.66
Figure I - 27. Condensation of cardanol with furfural and para-hydroxyacetophenone.66
44
4.2 Polyurethane resins
Polyurethanes (PU) are mainly used as coatings, adhesives and flexible or rigid foams. They are
obtained by the reaction of a polyol with a di- or polyisocyanate (Figure I - 28).
Figure I - 28. Synthesis of a polyurethane.
Cardanol is a good precursor for the synthesis of polyurethane resins considering its easy
conversion to polyol compound. The most current modification to obtain polyols from cardanol
relies on the reaction of the cardanol hydroxyl group or by condensation on the phenolic ring.
Furthermore, previous researchers reported the use of cardanol derivatives for the elaboration
of PU materials with enhanced thermal and mechanical properties. PU resins exhibiting good
thermal and mechanical properties were obtained for example from pre-synthetized cardanol-
formaldehyde resins,67-70 or from cardanol-furfural resins.71 Nevertheless, direct synthesis of
cardanol-based diols or polyols was also considered for the elaboration of cardanol-based PU
materials. These syntheses are detailed in the following paragraphs.
4.2.1 Synthesis of cardanol-based polyols
Cardanol-based diols (Figure I - 29) have been synthetized by reaction of cardanol hydroxyl
group with 3-chloropropane-1,2-diol,72 with epichlorohydrin,73 or by condensation of p-
aminophenol on cardanol.69 The two first syntheses resulted in the formation of aliphatic diols
while the third approach aimed at forming a molecule bearing two phenol moieties.
45
Figure I - 29. Chemical structures of cardanol-based diols a)72 b)73 c)69.
Cardanol-based polyols can also be synthetized by condensation reaction on the phenolic ring,
for example by reaction with oxazolidine (Figure I - 30),74 or with melamine and di-ethanolamine
(Figure I - 31).75
Figure I - 30. Synthesis of cardanol-based polyol by reaction with oxazolidine.74
The Mannich polyols synthetized by Ionescu et al. (Figure I - 31) were found to have a lower
viscosity (viscosity range of 3 to 5 Pa.s at T = 25 °C) than petrochemical Mannich polyols from
phenol and nonyl-phenol (25-30 Pa.s at T = 25 °C). Cardanol-based Mannich polyols were used
for the elaboration of rigid polyurethane foams with good mechanical and fire retardancy
properties. The Tg of the PU foams were found to be in the range of 110-120 °C. Thermal
degradation starts around 250 °C.
46
Figure I - 31. Synthesis of cardanol-based polyols by reaction with melamine and di-
ethanolamine.75
Flame retardant polyol with low viscosity were synthetized from reaction between cardanol,
melamine and di-ethanolamine (Figure I - 31).75 Rigid polyurethane foams were then elaborated
by reaction of the synthetized polyols with poly-isocyanates as curing agents and cyclopentane
as blowing agent. The introduction of the flame-retardant melamine moiety in the molecular
structure of cardanol-based polyol enhanced the thermal stability and the flame resistance of the
PU materials.
Low viscosity cardanol-based polyols were obtained by Suresh et al.73 exhibiting various range of
hydroxyl functionality values (Figure I - 32).
Figure I - 32. Synthesis of cardanol-based polyols by reaction with epichlorohydrin and
diethanol amine or with glycerol monochlorohydrin.73
47
For instance, a Cardanol-based triol was synthetized by epoxidation of the cardanol hydroxyl
group followed by a reaction with diethanol amine. Another type of cardanol based triol
compound was synthetized by the reaction between cardanol and glycerol monochlorohydrin.
The obtained polyols were characterised by a low viscosity. The corresponding PU materials
(with diphenyl methanediisocyanate) were rigid and exhibit good mechanical and thermal
properties with Tg = 98 °C.
Another way to synthetize polyols from cardanol is the chemical modification of the alkyl chain
unsaturations. Primary hydroxyl groups can be easily grafted onto the cardanol side chain either
by performic acid oxidation (Figure I - 33),76 or by thiol-ene coupling with 2-mercaptoethanol
(Figure I - 34).77
The cardanol-based polyols synthetized by Suresh et al. 76 (Figure I - 33) were evaluated in the
preparation of rigid polyurethane foams by reaction with 1,4-diazabicyclo[2.2.2]octane. Their
mechanical and viscoelastic properties were comparable to PU foams elaborated from
commercial polyols.
Figure I - 33. Synthesis of cardanol-based polyols by performic acid oxidation.76
The polyols from cardanol synthetized by Fu et al. 77 (Figure I - 34) were used for the elaboration
of PU materials by reaction with hexamethylene diisocyanate. The thermal properties of the
corresponding PU materials are gathered in Table I - 11.
48
Figure I - 34. Synthesis of cardano-based polyols by thiol-ene coupling with 2-
mercaptoethanol.77
Two kinds of polyols were synthetized from cardanol: CAP1 and CAP2 represented in Figure I –
34. The highest Tg was obtained for the PU foam from CAP1 with Tg = 31.6 °C, wheras for CAP2 Tg
= 16.1 °C (Table I – 10). The lower Tg of PU material from CAP2 compared to PU material from
CAP1 is probably due to the long carbon chain introduced on the phenolic hydroxyl group and
increasing the flexibility of the polymer chains. The degradation temperatures showed no
remarkable difference because the degradation process is mainly attributed to the cardanol chain
scission.
Sample Tg (°C) T10% (°C) Tmax (°C)
CAP1 31.6 302.5 346
CAP2 16.1 291.8 333
Table I - 10. Thermal of CAP1 and CAP2 based PU materials.77 (T10% is the temperature at 10
wt% weight loss and Tmax is the temperature at maximum rate weight loss).
4.2.2 Cardanol-based non-isocyanate PU
The handling of isocyanate raw materials and their use for the production of polyurethane
products has become an issue due to the high toxicity of isocyanate. In this context, the
development of non-isocyanate polyurethanes through the reaction of amines and cyclic
carbonates is of growing interest. The synthesis of cashew nutshell liquid (CNSL)-based urethane
polyols via a non-isocyanate route has been reported.78 Cyclic carbonate derivative of diglycidyl
ether of cardanol was obtained by addition reaction of high pressure CO2 followed by reaction
with primary hydroxylamines yielding to the formation of hydroxyl and urethane groups (Figure
49
I - 35). The so-synthetized polyols were then cured using hexametoxy methylene melamine as
hardener yielding PU materials.
Figure I - 35. Synthesis of CNSL-based urethane polyols via a non-isocyanate route.78
4.3 Epoxy resins
Epoxy resins are well-known high performance thermosets used in numerous applications such
as coatings, adhesives, composite matrix etc. due to their good thermo-mechanical, chemical and
electrical properties.79 The actual concern about the use of petroleum-based phenolic compounds
for chemical applications encouraged researchers to develop sustainable alternatives, among
them various modifications and the use of cardanol as epoxy pre-polymer were reported in the
literature.
Di- or poly-epoxy monomers from cardanol are commercially available (Cardolite – NC-514), and
are synthetized through a two-step reaction with cardanol as starting reagent (Figure I - 36). The
studies based on these monomers are detailed in Chap IV- 1.
Figure I - 36. Chemical structure of diglycidyl ether of cardanol – commercially available NC514
- from Cardolite Corporation.
50
Most of the time cardanol epoxidation is used for the enhancement of the properties of cardanol-
formaldehyde phenolic resins. Indeed, their properties can be improved by additional
polymerization of the epoxy groups. Furthermore the reaction of the epoxy group with various
compounds such as with carboxyl-terminated polybutadiene allows the enhancement of the
impact resistance of the resin (Figure I - 37).20-22
Figure I - 37. Proposed reaction between epoxy groups of cardanol and carboxyl-terminated
polybutadiene.22
Kanehashi et al. suggested the synthesis of epoxy pre-polymers from cardanol by epoxidation
with epichlorohydrin in basic conditions of the cardanol hydroxyl group, followed by a thermal
polymerization of the cardanol alkyl side chain double bonds. (Figure I - 38).25 Epoxy coating
materials are afterwards obtained by reaction/curing with various diamines at room
temperature.
Figure I - 38. Synthesis of epoxidized cardanol pre-polymer.25
Finally, an enzymatic synthesis was proposed as a green approach for the epoxidation of Cardanol
(Figure I - 39).80 The unsaturations of the alkyl chain were epoxidized by reacting with lipase in
the presence of acetic acid and hydrogen peroxide, prior to form a polymer with epoxy-
functionalized pending C15 chains through coupling of the phenol moieties with peroxidase and
hydrogen peroxide. Peroxidase was shown by the authors to polymerize meta-substituted
phenols such as cardanol with chemical selectivity. Peroxidase was thus used to obtain
polycardanol and epoxide-containing cardanol. During the epoxidation by lipase/H2O2/acetic
acid, some polycardanols are crosslinked due to highly oxidative environment. The amount of
crosslinked polycardanols is higher for the polymer (Route B) than for the monomer (Route A).
The route A rather the route B is thus recommended to produce epoxide-containing
polycardanols as prepolymer.
51
Figure I - 39. Synthesis of epoxidized cardanol and polycardanol. 80
Finally the as-synthetized prepolymers were cured with a phenalkamine to elaborate the final
crosslinked material. Film samples of 50 µm thickness were prepared on a glass slide. The
hardness of the resulting materials measured by pencil scratch technique revealed that the
hardness improved with increasing epoxy content suggesting that the epoxy groups play a major
role in the materials hardness. Epoxide-containing polycardanols reached the highest hardness
of 9 H when cured for 5 h at 150 °C, a higher value compared to a commercially available alkyl
resin coating at 4 H. Furthermore, the addition of a phenalkamine curing agent still enhanced the
hardness to the material up to 5 H within 2 h curing. Epoxide containing polycardanol resins were
thus demonstrated to be a viable bio-based alternative to phenol-formaldehyde resins for
applications requiring high hardness and mechanical durability.
4.4 Polybenzoxazine resins
Polybenzoxazine (PBz) resins are another class of high performance thermoset materials. They
are emerging since three decades, and due to their outstanding properties and to their mono-
component resin status, they are considered as promising substitutes to phenolic or epoxy resins.
Polybenzoxazine resins are obtained through the ring-opening polymerization of benzoxazine
(Bz) monomers. The synthesis of benzoxazine monomers is based on a Mannich-like reaction
between a phenolic compound and formaldehyde, followed by a ring-closure process on a
phenolic derivative (Figure I - 40).81
52
Figure I - 40. Synthesis of a benzoxazine monomer.81
Through its phenolic structure, cardanol appears as a suitable bio-based phenolic compound for
the synthesis of Bz monomers. Indeed, several works report the use of cardanol for the synthesis
of novel bio-based Bz monomers and their corresponding PBz materials. The studies dealing with
these cardanol-based monomers and thermosets are detailed in Chapter III.
5 Conclusion
This first chapter highlights that cardanol is an important industrial crop that can be used for
many applications. Furthermore, the presence of different reactive sites (phenol, unsaturation
etc.) makes it as versatile chemical platform to design a wide range of molecules with high added-
value applications such as surfactants, antioxidants or plasticizers to polymer precursors. In
particular, due to its intrinsic properties, cardanol has been widely used for the synthesis of bio-
based surfactants and for the elaboration of phenolic, epoxy, or polyurethane materials. More
recently, the use of cardanol for the design of benzoxazine monomers is gaining more and more
interest, since it tackles several issues frequently encountered with benzoxazine monomers such
as high melting temperatures or the high brittleness of the resulting polybenzoxazine materials.
The following chapters are highlighting various chemical modification strategies we designed to
access new cardanol-based derivatives to be used for the elaboration or reinforcement of
polymeric materials.
The chapter II deals with the synthesis of reactive ammonium cardanol-based surfactants and the
study of their reactivity for the preparation of clay composite materials with BADGE. In the
chapter III a new strategy for the elaboration of bio-based and processable Bz materials by
combining cardanol with other naturally occurring phenolics is reported and studied. Finally the
use of Bz resins for the macromolecular reinforcement of a cardanol di-glycidyl ether resin by the
elaboration of interpenetrating polymer networks will be investigated.
53
Chapter II: Surfactants from cardanol
1 Introduction
Due to its naturally amphiphilic structure, cardanol is an excellent candidate for the preparation
of surfactants, as it has been detailed in Chapter I – 3.2. Indeed, surfactants are amphiphilic
molecules constituted of a hydrophobic part (the tail) and a hydrophilic group (the head). The
C15 alkyl side chain provides an essential hydrophobicity while the slightly polar hydroxyl group
allows a wide variety of chemical functionalization.82 Notwithstanding this particularly adequate
structure, cardanol-based surfactants are just emerging as a green alternative to conventional
petroleum-derived nonylphenols for the preparation of surfactants.4, 30, 31, 44-49, 51 Surfactants are
largely used as detergents, wetting and/or foaming agents, emulsifiers or dispersants due to their
ability to lower the surface tension of a liquid, between two liquids or between a liquid and a solid.
They are also largely used as clay organomodifier for the elaboration of clay-polymer
nanocomposite materials. In the present chapter, we aimed at synthesizing new ammonium
cationic surfactants from cardanol displaying different reactivities. Then we studied their effect
on the exfoliation of Montmorillonite clay within Bisphenol A diglycidyl ether (BADGE) epoxy
thermoset for the elaboration of composite materials. A state-of-the-art about the elaboration of
silicate layered polymer composite materials, the compatibilization between clay minerals and
polymer materials (clay organomodification) as well as the choice of the surfactant kind will be
introduced in the following part.
1.1 Preparation of nanocomposite materials
With the aim of improving polymeric materials properties, numerous researchers studied the
dispersion of compatible inorganic materials within the polymeric matrix. The addition of
particles as fillers leads to improvement of the material thermal, mechanical or conductive
properties such as stiffness and toughness, barrier effect or fire resistance. A large range of
natural and synthetic fillers are available for their elaboration. (Table II – 1).83
54
Chemical nature Filler examples
Element Graphite
Metal chalcogenides (PbS)1.18, (TiS2)2, MoS2
Carbon and Carbon oxides Graphite, Graphite oxide, Carbon Nanotubes
Metal phosphates Zr(HPO4)
Clays and layered silicates Montmorillonite, hectorite, saponite,
fluoromica, fluorohectorite, Vermiculite, kaolinite, magadiite
Layered double hydroxides M6Al2(OH)16CO3·nH2O, M=Mg, Zn
Other Nanocellulose, Nanochitin
Table II - 1. Example of fillers for the elaboration of nanocomposites.83
The pioneer work of the Toyota research group (1990) on polyamide 6 reinforced with
alkylamonium-modified Montmorillonite (MMT)84, 85 opened the gate to the use of clays and
layered silicates as polymer fillers. More particularly, polymer-layered crystal nanocomposites
are a class of composite materials. These materials are obtained by the intercalation of the
polymer within the particles layers. Such materials can be defined as nanocomposites when the
dispersed clay particles are sized in the range of nanometres (Less than 100 nm). It is noteworthy
that a homogeneous dispersion of clay is essential to an efficient reinforcement of a composite.
The percentage of clay needed to enhance the thermal and mechanical properties of polymer
layered silicate nanocomposite is very low (2 to 5 wt %). As a consequence, a great advantage of
these materials is their light weight.
Among the possible polymeric materials available for the elaboration of nanocomposites, the
study of epoxy based polymeric matrix has been significant. Indeed, epoxy thermosets are
broadly used in adhesives and coatings. Nevertheless, high performance applications are hardly
reached with non-modified epoxy thermosets.79 The elaboration of epoxy composites, by the
incorporation of layered silicate filler particles, was shown to lead to an enhancement of the
materials properties86 and was thus widely studied. 83, 86-90 The mechanical properties of lamellar
silicate-modified epoxies are strongly dependent on the fillers size, organophilic treatement and
on their intercalation/exfoliation state within the final material.79
1.2 Structure and properties of clay and layered silicates as fillers
Clay and lamellar silicates, especially the smectite type - 2:1 clay minerals - are widely available
and the most commonly used as natural fillers. More particularly, MMT clays have several assets
which justify their wide use: a high cation exchange capacity (CEC, meq/100g), a multiscale
organization (Figure II - 1a), good swelling properties in water and a large surface area.91, 92 The
distinctive structure of MMT clay consists in platelets each composed of two tetrahedral silica
55
sheets -SiO4- framing an octahedral alumina sheet -Al(OH)3- (Figure II - 1b), separated by
metallic cations.
Figure II - 1. Schematic representation of a) MMT multi-scale organization,93 and b) MMT
crystallographic structure.89
Through isomorphic substitutions of structural ions within the MMT sheets, a charge deficiency
is created. Indeed, some ions within the platelet sheets can be replaced by lower charged ions.
For instance, Al3+ can be replaced by Fe2+ or Mg2+. The MMT platelets are thus globally negatively
charged. Consequently, exchangeable counter-ions are present in the interlayer space between
the platelets in order to insure the clay platelets electro-neutrality. The nature of the cations and
their hydration are mostly determining the interlayer dimension. The interlayer distance
between two platelets is described as a basal spacing d001. In the case of MMT clay the interlayer
cations are essentially hydrated Na+ and Ca2+, conferring a hydrophilic character to the MMT clay.
As polymeric materials, such as epoxies, are generally characterised by a hydrophobic behaviour,
the modification of the clay minerals hydrophilic property is essential for adequate matrix-filler
compatibility. Indeed, the properties of nanocomposite materials are strongly impacted by the
morphology and the filler dispersion state within the polymeric matrix.83, 94 Depending on the
polymer-clay compatibility several dispersion states can be obtained (Figure II - 2).83
56
Figure II - 2. Schematic representation of a) phase separated microcomposites, b) intercalated
nanocomposites, and c) exfoliated nanocomposites.
Phase separated composites are obtained (Figure II - 2a) when the polymer is not able to
intercalate the MMT sheets. Aggregates or tactoids of primary particles of MMT are dispersed
within the polymeric matrix and a microcomposite-like behaviour is observed. An intercalated
state (Figure II - 2b) is reached when the polymer is able to spread between the clay platelets
layers, increasing the basal distance by keeping an ordered structure with alternate layers of clay
and polymer. The exfoliated state (Figure II - 2c) is obtained when the polymer is able to
intercalate the clay platelets layers or when monomers are intercalated between the clay platelets
prior their polymerization. The clay layers become totally independent and the crystallographic
orientation is lost. Both intercalated and exfoliated states correspond to nanocomposite materials
with an improvement of the corresponding neat polymeric material properties. Nevertheless, the
exfoliated state appears to be the most efficient in terms of mechanical and barrier properties
enhancement95, 96 and a particular attention has been paid to the understanding of the exfoliation
mechanism of lamellar silicates, especially for MMT clay.97, 98 Indeed, in order to obtain an
exfoliated structure it is essential to enhance the clay-polymer compatibility and to promote
either the intercalation of the polymer chains or the in-situ polymerisation of monomers within
the interlayer space. The surface modification of the clay mineral by an organic compound
(organomodification) represents a widely studied approach.88, 99
57
1.3 Clay organomodification strategies
Elaboration of MMT nanocomposites by direct polymer intercalation is hardly reached due to
their discordant properties. Indeed, most of the polymers are hydrophobic whereas pristine MMT
clay is hydrophilic due to the presence of hydrated metallic cations within the sheets interlayer
space. The elaboration of MMT nanocomposites requires thus the clays organomodification. For
the last two decades, many works report on the investigation of MMT exfoliation mechanism in
polymers and how to drive them.94, 98, 100
Through its particular structure composed of lamellar sheets, the MMT modification to
hydrophobic/more organophilic compound is easily achievable. Clay organomodifications can be
achieved predominantly by two processes: (1) a non-covalent grafting (by a cationic exchange of
the interlayer cations with cationic surfactants) or (2) a covalent grafting (reactive groups
towards the polymer are bonded on the edge or on the surface of the clay platelets).101
In the following part, we will mainly focus on the clay organomodification strategies for the
reinforcement of epoxy resins.
1.3.1 Clay organomodification by cationic exchange reaction
MMT clay organomodification is generally achieved by cation exchange reaction. Indeed, the
interlayer cations insuring electronegativity of the materials are easily exchangeable, particularly
with organic ammonium or phosphonium-based surfactants.100, 102, 103 These alkylammonium or
alkylphosphonium cations allow lowering the surface energy of the clay minerals galleries and
the wetting properties of polymer matrices towards the organomodified MMT are thus improved.
The most used cationic surfactants for the organomodification of MMT clay as filler for epoxy
nanocomposites are ammonium-based surfactants, particularly quaternary ammonium ones.
Indeed, the hydration of quaternary ammoniums is lower than those of primary ammoniums and
their desorption is thus minimized. Notwithstanding, an exfoliated state is hardly reached if an
additional chemical catalysis is not provided.104 Indeed the polymer growing or networking
kinetics must be higher within the clay mineral interlayer spaces compared to outside otherwise
there might be a rate competition between the platelets exfoliation and the polymer matrix
gelation during polymerization.105 Indeed, when the polymerization rate is higher in the
interlayer galleries than in the outside, the formation of an intragallery polymer network is firstly
initiated and the limited polymer network (outside the clay interlayer) remains sufficiently
mobile to facilitate further migration of the monomers into the clay interlayer galleries for further
exfoliation. In the case of epoxy as polymeric matrix, a correlation has been found between the
surfactant Lewis acidity and a catalytic growth of the epoxy network, favouring the clay mineral
layers separation (exfoliation) in the following order: CH3(CH2)17NH3+ > CH3(CH2)17N(CH3)H2+ >
58
CH3(CH2)17N(CH3)2H+ > CH3(CH2)17N(CH3)3+.105, 106 Primary ammonium surfactants are thus
favouring the clay exfoliation within an epoxy matrix through acid catalyses, whereas quaternary
ammonium surfactants tend to lower hydration and desorption of the surfactants. This
correlation highlights the difficulty to select the appropriate type of surfactant.
Figure II - 3. Schematic representation of the monomer inclusion within MMT, followed by in-
situ polymerization to reach MMT exfoliation.
Furthermore, the exchange between interlayer cations and organic surfactants allows not only
the clay modification from a hydrophilic to a hydrophobic character but also the modification of
the interlayer spacing. Indeed, the interlayer distance is also an essential parameter to consider
for the elaboration of nanocomposite materials. Actually, most of the nanocomposite materials
are elaborated by direct intercalation of polymers from solution or melts within the clay
interlayer space, as well as by the inclusion of monomers that polymerize in the interstice (Figure
II - 3).101
The formation of exfoliated clay nanocomposites is strongly dependent on the nature of the
alkylammonium cations. Indeed, longer linear alkyl chains facilitate the formation of
nanocomposites. 8 to 15 carbon long alkyl chains surfactants are essential to adequately push
apart the clay mineral layers to allow the polymer chains or monomers to diffuse within the clays
galleries and to obtain an exfoliated state. Lan et al. 107 reported the organomodification of MMT
clays with ammonium surfactant of different alkyl chain length and the elaboration of
nanocomposite materials with BADGE cross-linked by Jeffamine D2000. They highlighted the
relation between the ammonium clay organomodifier chain length and the clay exfoliation.
Indeed, in the case of MMT clay modified with CH3(CH2)7NH3+, the clay galleries hydrophobicity
is relatively low and the interlayer space is narrow. The amount of intercalated epoxide and
amine cross-linker is thus insufficient to achieve exfoliation. The phase dispersed in the
59
composite resulting from CH3(CH2)11NH3+ organomodified MMT and the epoxy matrix is a
mixture of exfoliated clay platelets and clay primary particles. On the contrary, MMT clay
organomodified with CH3(CH2)17NH3+ surfactant allowed the intercalation of epoxide monomers
and amine cross-linkers within the clay interlayer galleries, and lead thus to the formation of
exfoliated clay platelets based nano-composite.
1.3.2 Clay organomodification by cationic exchange reaction and covalent grafting
Beside the compatibility enhancement provided by the cationic exchange with surfactants, clay
minerals could also be made compatible towards epoxy precursors. Indeed, when the clay is
modified with amine, anhydride or carboxylic groups for instance, the epoxy monomers could
react with the reactive groups and the polymer network could grow within the interlayer space.79
To this aim, several researchers modified MMT clay for instance by covalent grafting of
organosilane compounds with various functionalities onto the hydroxyl groups on platelet
surfaces or edges. The grafted organosilanes may be reactive toward epoxy polymers for example
if they are bearing amine, anhydride or carboxylic groups.108-111
Nevertheless, Le Pluart et al.108 highlighted the possible reaction of covalent grafted
organosilanes on the layer edges between themselves leading to a collapse of the mineral layers
and preventing their exfoliation. The clay organomodification by cationic exchange prior to the
covalent grafting of functionalized organosilane compounds should be favoured. Indeed, the prior
organomodification would increase the interlayer spacing, helping thus the diffusion of the
organosilane compounds (and afterward epoxy monomers) within the interlayer space and
favouring thus their covalent grafting on the platelets surfaces and afterwards the platelets
exfoliation.
As described previously, the clay organomodification by a cationic surfactant is essential to
change the clay hydrophilic character to a more organophilic character, as well as to enhance the
clay platelets interlayer space. On the other hand, the covalent grafting of functionalized
organosilane compounds onto the clay platelets allow the easy introduction of reactive functions
towards epoxy compounds, favouring their polymerization within the clay platelets.
Le Pluart et al. proposed the modification of MMT clay by combination of cationic exchange and
covalent grafting reactions.108 The MMT clay interlayer space and hydrophobic property were
modified by the introduction by cationic exchange reaction of dimethylbenzylammonium
surfactants. The MMT clay was then further modified by the grafting of amino-silane compounds
-reactive towards epoxy polymers- onto the hydroxyl groups situated on the surfaces and edges
of the MMT clay platelets (Figure II - 4).
60
Figure II - 4 Grafting of an amino-silane compound on prior organomodified MMT clay.108
Nevertheless, surfactants could also bear other reactive functions and could thus be able to take
part in polymerization reactions with various polymer kinds. This strategy developed by Pluart
et al. paved the way to a convenient clay organomodification method by modifying clay minerals
through the incorporation of reactive surfactants. This strategy is studied in the following work.
1.4 Cationic surfactants from Cardanol
As described previously, mostly cationic surfactants are used for clay organomodification by
cationic exchange reaction. To date, only two studies on cardanol-based cationic surfactants were
reported in the literature. A hydrogenated cardanol-based quaternary ammonium with the
quaternary ammonium placed at the end of the alkyl chain was synthetized and used as a phase
transfer catalyst (Figure II - 5).49
Figure II - 5. Chemical structure of cardanol-based quaternary ammonium surfactant from De
Avellar et al.49
Verge et al. 51 reported the synthesis of a cardanol-based ammonium surfactant (Figure II - 6)
from the commercially available cardanol mono-epoxy derivative NC-513 (Cardolite
Corporation).
61
Figure II - 6. Synthesis of cardanol-based ammonium surfactant from the cardanol mono-epoxy
derivative NC-513.51
This surfactant issued from cardanol was particularly appropriate to enhance the compatibility
between sepiolite, a needle-like clay mineral, and conventional Bisphenol A diglycidyl ether (1,4-
diaminocyclohexane - DAC - as hardener). The specific structure of the cardanol-based surfactant
enabled the modification of sepiolite clay through cation exchange reaction. Furthermore, free
NH2 and OH reactive groups on the surfactant allowed the reaction with epoxy monomers onto
the clay surface, improving the compatibility between clay and epoxy and promoting the growing
of the polymer network between the sepiolite needles. Thus, the organomodification of sepiolite
clay by the cardanol-based surfactant (PkH+) led to a good dispersion of the clay needles within
the BADGE polymeric matrix, in comparison to non-modified sepiolite clay (SEM analysis, Figure
II – 7).
Figure II - 7. Scanning Electron Micrographs of BADGE/DAC polymer network filled with a) 5
wt% neat sepiolite and b) 5 wt% sepiolite organomodified by PkH+.51
Moreover, the good dispersion of sepiolite clay needles within the polymeric matrix led to an
enhancement of the material thermo-mechanical properties. Indeed, the Tg was shifted to higher
temperature (from 180 °C to 195 °C) and the storage modulus was increased from 4.0 to 4.8 GPa
at 50 °C.
62
Based on these previous results, three different ammonium surfactants were prepared from
epoxidized cardanol NC-513. In a first time the effect of the cardanol-based surfactants on the
Montmorillonite clay organomodification was investigated. Then, their amino group content and
reactivity towards the BADGE epoxy matrix were studied as a benefit or a drawback to the
exfoliation of MMT layered clay mineral within a BADGE epoxy matrix. Indeed, the surfactant
activity towards BADGE could either help the MMT layer exfoliation or even aggregate those.112
These results are presented in the following section.
2 Results and discussion
The detailed experimental conditions are reported in annex p181.
2.1 Surfactants synthesis
As described in the previous part, keeping an amino-multifunctionnality is essential to promote
the clay oragnomodification in a first time, and the polymer growth within the clay platelets in a
second time. Primary and secondary amine groups available within the surfactant would allow
the grafting of epoxy compounds within the organomodified clay, improving thus the polymer
intercalation and growth within the clay. This first part, focused on the amino-multifunctionnality
of cardanol-based surfactants, specially tailored to highlight the surfactant reactivity–to–clay
exfoliation relationship. Three surfactants were prepared from an epoxy derivative of cardanol
(NC-513) with amino compounds of different amine functionalities toward epoxies.
The same conditions were applied to synthetize each surfactant (Figure II - 8). The cardanol-
based surfactants were synthetized through nucleophilic addition of a primary amine on the
epoxide group of NC-513 in chloroform. The amine was added in excess to the media in order to
favour the mono-addition of cardanol on the amine compound. Indeed, it is preferred to keep the
maximum of reactive (free) primary and secondary amine functions on the surfactant so that they
may be able to react once they are incorporated to the clay. Depending on the amine functionality,
cardanol-based surfactants CardS1, CardS2 and CardS3 were synthesized.
Tris(2-aminoethyl)amine (TAEA) was used as reagent for the synthesis of the CardS1 surfactant
with a functionality of 5 (f = 5) (because two free primary -NH2 functions accounting for 4 and
one secondary -NH function are available, accounting for 1). The use of ethylene diamine (EDA)
allowed the synthesis of the CardS2 surfactant with a functionality of 3 (f = 3) (one free -NH2 and
one free -NH functions). Finally, the CardS3 surfactant with a functionality of 1 (f = 1) was
synthetized with N,N-dimethylethylenediamine (DMEDA) (one free –NH function). The synthesis
and the chemical structures of the surfactants are displayed on Figure II - 8.
63
A family of novel cardanol-based ammonium surfactants, with increasing amino functionalities
towards epoxy, were thus synthetized: CardS1 (f = 5) > CardS2 (f = 3) > CardS3 (f = 1).
Figure II - 8. Schematic representation of the synthesis of the Cardanol-based surfactants.
2.2 Characterization of CardSx surfactants
2.2.1 Fourier Transform Infrared spectroscopy (FTIR)
The FTIR spectra of CardS1, CardS2 and CardS3, are depicted in Figure II - 9a, b &c respectively.
The FTIR spectra of all CardSx materials were very similar, as expected due to their close chemical
structure.
64
Figure II - 9. FTIR spectra of a) CardS1, b) CardS2, c) CardS3.
The characteristic peaks of the cardanol compound were observed, especially aromatic C-H
stretching at 3009 cm-1, strong CH2 and CH aromatic and aliphatic absorption band at 2927-2854
cm-1 arising mainly from the long alkyl chain and aromatic C-H out of plane deformations at 1637
cm-1. In addition, characteristic peaks of amine functions were also observed, such as N-H
stretching absorption band at 3287 cm-1, C-N stretching at 1101 cm-1, and the ethers C-O
stretching at 1048 cm-1.
2.2.2 Characterization by 1H NMR
1H NMR characterization was achieved to further confirm chemical structures of the cardanol-
based surfactants. The quantitative results for each CardSx compound are reported and the NMR
spectra are depicted in Figure II - 10 for the case of CardS1 and in the Figure II - 11 and - 12 for
CardS2 and CardS3 respectively.
65
The signal due to the aromatic protons at δ= 6.50-7.25 ppm was used as integration reference for
4H. The expected theoretical integrations were calculated by moderation based on the abundance
of unsaturation described in the literature.11 Nevertheless, cardanol-based products are
composed of four molecules differing by the unsaturation degree of their alkyl chains. These
unsaturation abundances can slightly vary regarding the origin and the processing of the CNSL
based bio-product for the manufacturing of NC-513. The assignments depicted in Figure II - 10
are based on a previous work50 and from a study on Cardanol-issued polyurethane resin
described in reference.70 To simplify, the experimental and theoretical integrations will be noted
Iexp and Ith respectively.
The NMR spectrum of CardS1 is displayed in Figure II – 10.
Figure II - 10. CardS1 1H NMR spectrum (Solvent CDCl3).
For each surfactant, the characteristic peaks of cardanol were observed, especially the aromatic
protons [1, 2, 3, 4] at 7.15 and 6.75 ppm (used as integration reference), the alkyl chain olefinic
CH2 protons [b2, d2, e2, g2, h2, a2] at 5.81, 5.35, and 5.03 ppm, the protons in α of the alkyl chain
unsaturations [c2, f2, i2] at 2.04 ppm, as well as the CH2 protons in α of the aromatic [o] at 1.59
ppm, the CH2 from the alkyl chain [b1, c1, d1, e1, f1, g1, h1, i1, j, k, l, m, n] at 1.31 ppm and the CH3 of
the alkyl chain at 0.91 ppm. The CH2 of the alkyl chain comprised between two unsaturations [c3,
f3] were detected at 2.28-2.95 ppm, together with CH2 protons from the used amine moiety. The
experimental and theoretical integrations of the CardS1 peaks are reported in the Table II - 2. As
66
it can be observed, the experimental integrations of the peaks corresponding to the cardanol
moiety were close to the expected integrations for a mono-addition of NC-513 on TAEA.
Beside the characteristic peaks from the cardanol moiety, the reaction of the NC-513 epoxy group
with the TAEA amine to yield CardS1 was confirmed by the presence of peaks at 3.84-4.23 ppm
corresponding to H in α to oxygen [5, 6]. Their integration corresponds to an opened epoxy cycle
as they integrated for Iexp = 3.5 H (Ith = 3 H). Furthermore, peaks corresponding to the TAEA
compound were also readily observed. The peaks at 2.28-2.95 ppm, Iexp = 15.6 H, Ith = 16.1 H,
corresponded to the CH2 [7, 8, 9, 10, 11] of TAEA combined to the CH2 between two unsaturations
of NC-513 [c3, f3]. The primary amines of TAEA [12] appeared at 3.4 ppm with Iexp = 4.3 H (Ith = 4
H), confirming the mono-addition of NC-513 on one TAEA moiety.
Chemical shift
(ppm) Assignment Iexperimental Itheoretical
0.91 Alkyl chain CH3 1.8 H 1.7 H
1.31 Alkyl chain CH2 13.5 H 13.6 H
1.59 -CH2-Ar 2.3 H 2H
2.04 -CH2*=CH- 3.4 H 3.1 H
2.28 – 2.95
Amine moiety –CH2-
and cardanol moiety
=CH-CH2*-CH=
15.6 16.1
3.04 -NH2 4.3 4
3.84 – 4.23 H in α to O 3.5 3
4.93 – 5.90 Alkyl chain CH= 4.8 4.5
6.68 – 7.21 H-Ar 4 4
Table II - 2. CardS1 experimental and theoretical integrations.
The characteristic peaks from the cardanol moiety were also observed for the CardS2 compound
(Figure II – 11). The experimental integrations were very close to those of the theoretical
integrations and to the integrations found for CardS1. (Table II - 3)
The mono-addition of NC-513 on EDA was confirmed by the integrations and the presence of te
peaks at 3.86-4.30 ppm, Iexp = 3.4 H, Ith = 3 H, corresponding to reacted epoxy ring protons in α of
oxygens [5, 6], the peaks at 2.47-2.93 ppm corresponding to the CH2 [7, 8, 9] of EDA combined to
the CH2 between two unsaturations of NC-513 [c3, f3] for which Iexp = 8.5 H and Ith = 8.1 H, and the
peak at 3.18 ppm, Iexp = 2.5 H, Ith = 2H corresponding to the NH2 of EDA [10].
67
Figure II - 11. CardS2 1H NMR spectrum (Solvent CDCl3).
Chemical shift
(ppm) Assignment Iexperimental Itheoretical
0.91 Alkyl chain CH3 1.8 H 1.7 H
1.32 Alkyl chain CH2 13.0 H 13.6 H
1.61 -CH2-Ar 2.2 H 2H
2.04 -CH2*=CH- 3.3 H 3.1 H
2.47 – 2.93
Amine moiety –CH2-
and cardanol moiety
=CH-CH2*-CH=
8.6 8.1
3.18 -NH2 2.5 2
3.86 – 4.30 H in α to O 3.4 3
4.90 – 5.93 Alkyl chain CH= 4.7 4.5
6.64 – 7.25 H-Ar 4 4
Table II - 3. CardS2 experimental and theoretical integrations.
Finally for the CardS3 compound, the peaks corresponding to the cardanol moiety were also
observed on the NMR spectra, and their integrations were consistent with a mono-addition of NC-
513 on an amine compound such as for CardS1 and CardS2. (Table II - 4).
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The mono-addition of NC-513 on DMEDA was further confirmed by the following peaks: the CH2
[7, 8, 9] of DMEDA combined to the CH2 between two unsaturations of NC-513 [c3, f3] for which
Iexp = 13.6 H and Ith = 14.1 H, the protons of reacted epoxy ring protons in α of oxygens [5, 6] at
3.86-4.30 ppm, Iexp = 3.4 H, and Ith = 3 H.
Figure II - 12. CardS3 1H NMR spectrum (Solvent CDCl3).
Chemical shift
(ppm) Assignment Iexperimental Itheoretical
0.91 Alkyl chain CH3 1.8 H 1.7 H
1.32 Alkyl chain CH2 13.5 H 13.6 H
1.61 -CH2-Ar 2.2 H 2H
2.04 -CH2*=CH- 3.6 H 3.1 H
2.47 – 2.93
Amine moiety –CH2-
and cardanol moiety
=CH-CH2*-CH=
13.6 14.1
3.86 – 4.30 H in α to O 3.4 3
4.90 – 5.93 Alkyl chain CH= 4.9 4.5
6.64 – 7.25 H-Ar 4 4
Table II - 4. CardS3 experimental and theoretical integrations.
For all the characterized compounds, the experimental integrations were slightly varying from
the expected integrations. This is due to the fact that cardanol is a natural-occurring compound
69
with diverse compositions, which lead to complex NMR spectra. Nevertheless, the number of
aromatic protons is a good reference because only the cardanol is bearing aromatic protons. Thus
for a mono-addition of NC-513 on TAEA for example, only 4 aromatic H should be observed. In
the present case, the estimation of 4 aromatic H as integration reference seemed to be correct, as
4.53 aromatic H were integrated for the integration of the global CardS1 corresponding spectrum
(Total number of proton: exp = 54.67 / th = 55).
In conclusion, the NRM spectra and the integrations let pretend to a majority of mono-addition of
NC-513 on the different amine-containing molecules, confirming the structures of the synthetized
surfactants obtained by IR characterization.
2.2.3 Characterization by MALDI-TOF/MS
The chemical structures of the three synthetized surfactants were further characterized by
MALDI/TOF-MS analysis. The surfactant experimental mass could thus be compared to the
expected mass in order to fine-tune their chemical structure.
In order to characterize the molecules, α-cyano 4-hydroxycinnamic acid (CHCA) was used as
protic matrix for MALDI-MS analysis. By using this matrix, only the protonated molecule should
be detected.
Cardanol is a product composed of four different molecules, varying through their alkyl chains
unsaturation degree. As a result, the MALDI-MS spectrum obtained from compounds synthetized
from cardanol displayed a fingerprint pattern, allowing the easy recognition of cardanol-
containing compounds by MALDI-MS analysis.51 For example, in the case of the CardS1
compound, synthetized with TAEA (M = 146 g/mol), a peak spreading from 501 to 507 m/z was
expected for the mass peak of a mono-addition of TAEA on the epoxidized cardanol [CardS1+H]+.
Indeed, the molar mass of NC-513 is varying from M = 354 g/mol and M = 360 g/mol, depending
on the alkyl side chain unsaturation degree.
For each surfactant, the MALDI-MS analysis in Figure II – 13a, c & e gave rise to an intense peak
assigned to the mono-addition of the epoxy derivative of cardanol (NC-513) moiety onto the
amine-containing reagent (chemical formula in Figure II – 8). For instance, the MALDI-MS
analysis of the CardS1 compound revealed as expected the mono-addition of NC-513 on TAEA, as
the corresponding peak could be observed at 501 m/z (Figure II – 13a). Similarly, the mono-
addition of NC-513 on EDA (CardS2) and DMEDA (CardS3) were confirmed by the presence of the
corresponding peaks at 415 and 443 m/z respectively.
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The mass for each Cardanol-based surfactant were in accordance with their expected structure,
and the protonated mono-addition compounds of NC-513 on the various amine-containing
reagents were the main detected compounds.
Figure II - 13. MALDI-MS spectra of CardS1 using a) CHCA & b) DCTB as matrix, CardS2 using
c) CHCA & d) DCTB and CardS3 using e) CHCA & f) DCTB as matrix.
In addition, to the MALDI-MS analyses with CHCA as protic matrix, MALDI-MS analysis using
Trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) as matrix
were also achieved and are reported in Figure II - 13b, d & f.
Additional MALD-MS analyses using DCTB as matrix were achieved in order to validate the
structural features of the obtained surfactants and to highlight their available amine
functionalities. Indeed, DCTB is known to react with primary and secondary amines both in
solution and in the gas phase, to produce molecule-matrix adducts, characterized by +184 Da
shifted peaks (proportionally to the number of N-H bonds).113 In this reaction, an amino group of
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the surfactant replaces the dicyanomethylene group of DCTB forming a matrix adduct via a -C=N-
bond (Figure II – 14). As DCTB is not a protic matrix, silver (Ag) was added to the molecule-
matrix mixture in order to protonate them for their detection.
Figure II - 14. Proposed mechanism for DCTB adduction to an aliphatic primary amine.113
These side reactions with DCTB were readily observed here for all the three surfactants in
satisfactory accordance with their structures and the content of amino groups. DCTB was only
able to react four times on CardS1 (f = 5) with characteristic peaks observed at 685.5 m/z [CardS1
+ H + 1 x 184 Da], 869.7 m/z [CardS1 + H + 2 x 184 Da], 1237.9 m/z [CardS1 + H + 4 x 184 Da].
Nevertheless, the fifth addition of DCTB on CardS1 could be expected for this compound. This last
reaction was probably impeded by the sterical hindrance. An amine functionality of f = 4 will thus
be considered for CardS1 in the rest of this study. The DCTB matrix reacted as expected three
times on CardS2 (f = 3) and one time on CardS3 (f = 1) characterized by the peaks observed at
599.5 m/z [CardS2 + H + 1 x 184 Da] and 967.7 m/z [CardS2 + H + 3 x 184 Da] for CardS2 and at
627.5 m/z [CardS3 + H + 1 x 184 Da] for CardS3.
These characterizations by MALDI-MS analysis using DCTB as matrix corroborated the
surfactants structures identified with CHCA matrix, and further validated their amine
functionalities.
In conclusion, MALDI-MS analyses confirmed both the mass of the expected chemical structures
and the amine functionalities of the synthetized cardanol-based surfactants. The effective amine
functionalities available on each surfactant can be summarized as follow: CardS1 (f = 4) > CardS2
(f= 3) > CardS3 (f = 1).
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2.3 MMT clay organomodification and characterization
2.3.1 O-MMT preparation procedure
MMT clay is widely used for the reinforcement of epoxy thermosets and was thus chosen for the
elaboration of composite materials. As described previously, MMT is a hydrophilic compound,
whereas epoxy compound is hydrophobic. In order to improve the epoxy-clay compatibility, it is
essential to modify the hydrophilic MMT to a more hydrophobic compound. This modification of
the MMT hydrophilic property can be achieved by its organomodification by the pre-synthetized
ammonium cardanol-based surfactants.
Each of the synthetized surfactant was used for the organomodification of MMT by standard
cation exchange procedure. 2 mole equivalent in regards to the MMT’s Cationic Exchange
Capacity (CEC = 116 g/mol) were used for the organomodification procedure.
In a first step, the surfactants (2 equivalents to the MMT’s CEC) were protonated in an EtOH/HCl
solution. The protonated surfactant solution was added in a second step to the MMT clay (1
equivalent), previously dispersed in H2O. The obtained O-MMT was filtrated and washed with
ethanol/water solution, and further freeze-dried. The protonation is known to preferably occur
on tertiary and secondary amines (more basic than primary amines). The resulting O-MMT
products are noted CardS1-MMT, CardS2-MMT and CardS3-MMT.
2.3.2 Characterization of O-MMT by X-ray diffraction (XRD)
With the aim to confirm the MMT organomodification by cationic exchange reaction, XRD
characterization was carried out. The exchange between the MMT interlayer cations and the
synthesized surfactants should modify the interlayer spacing. So, the interlayer distance has been
tracked on MMT and O-MMT by XRD analysis (Figure II - 15).
73
Figure II - 15. X-Ray diffractograms of pristine MMT and O-MMT.
The XRD diffractogram of non-modified MMT showed a diffraction peak at 2θ = 7 ° (d = 12.6 Å).
The diffractograms of O-MMT showed all diffraction peaks at lower angles: 2θ = 4 ° (d=22.1 Å),
2θ = 4.2 ° (d=21 Å), 2θ = 4.5 ° (d=19.6 Å) for CardS1-MMT, CardS2-MMT and CardS3-MMT
respectively (Figure II - 15), meaning that the interlayer spaces were quite similar for each clay
mineral as expected due to the close chemical structures of each surfactant.
In conclusion, the interlayer spacing increasing from 12.6 Å for the pristine MMT to around 20-
22 Å for the O-MMT witnessed the efficient ion exchange between interlayer cations and
cardanol-based surfactants, confirming thus the efficient MMT-organomodification.
2.3.3 Characterization of O-MMT by MALDI-TOF/MS
The O-MMT clay was characterized by MALDI-MS (DCTB-Ag matrix) to verify that the surfactant
was present within the clay platelets. Indeed, after the clay organomodification by cationic
exchange, the surfactants should be present within the clay platelets in their protonated form.
The clay platelets are not protonated, and thus not detected by MALDI-MS.
As compared to the native surfactants, the MALDI analyses (DCTB-Ag matrix) of O-MMT resulted
in completely different mass spectra (Figure II – 16).
74
Figure II - 16. MALDI-MS spectra, using DCTB-Ag as matrix, of a) CardS1-MMT, b) CardS2-
MMT, and c) CardS3-MMT.
As depicted on Figure II - 16a for CardS1-MMT, the protonated surfactant was readily detected
within the MMT clay at m/z 501. As mentioned earlier, DCTB is known to react with primary and
secondary amines both in solution and in the gas phase, to produce molecule-matrix adducts,
characterized by +184 Da shifted peaks (proportionally to the number of N-H bonds).
Nevertheless, a unique +184 Da mass shift (addition of DCTB) was observed. Indeed, the presence
of amonium function was shown to reduce or fully avoid the DCTB side reaction.113 In comparison,
for neat CardS1 (not within the clay), the protonated specie was poorly detected and an amine
functionality of f = 4 was found because 4 additions of DCTB on the molecule were detected (Chap
II, 2.2.3; Figure II - 14). Both observations were thus in accordance with the presence of species
of CardS1 protonated prior to the mixing with the DCTB matrix and any irradiation and mass
analysis. In consequence, it can be concluded that the CardS1 surfactant was present in its
protonated form within the MMT clay. Similar results were obtained for MMT-CardS2 and MMT-
CardS3 (Figure II - 16b and - 16c respectively), both of them were detected as protonated
species at m/z 415 and 443, respectively, while the reaction with DCTB was completely avoided
75
(no +184 Da mass shift). The CardS2 and CardS3 surfactants were thus also shown to be present
in a protonated form (prior to irradiation and mass analysis in presence of DCTB) within the MMT
clay.
In conclusion, the XRD analysis of the O-MMT revealed increased interlayer spacing, conveying
the effective organomodification of the clay by the three surfactants. Furthermore, the three
surfactants were found by MALDI-MS analysis to be present in their protonated form within the
O-MMT clay, further confirming the efficient clay organomodification by the synthetized
surfactants. Nevertheless, the fact that the surfactants were in their protonated form within the
O-MMT clay and that they do not further react with DCTB suggest a different reactivity towards
the BADGE epoxy – i.e. the available amino functionalities (AAF).
2.4 Evidence of the surfactant amino-multifunctionnality within MMT clay
The MALDI-MS (DCTB-Ag matrix) analyses results of the surfactants within MMT clay (CardS1-
MMT, CardS2-MMT, and CardS3-MMT) supposed a change in the surfactant available amine
functionalities. Indeed, their protonated form seemed to influence on the availability of the amine
functions of the surfactants to further react with the BADGE epoxy. In order to determine the
available amine functionality of the surfactants (free to further react with epoxy matrix) once
incorporated within the MMT clay, a mono-functional furfuryl glycidyl ether (Fge, Figure II - 17)
was added to the O-MMT clay.
Figure II - 17. Chemical structure of furfuryl glycidyl ether (Fge).
The epoxy group of Fge is supposed to react with the neutral primary and secondary amines of
the surfactants (Figure II - 18).
Figure II - 18. Reaction between epoxy and primary and secondary amine functions.
The detection by MALDI-MS analysis of the amount of Fge compound grafted on each surfactant
will allow the determination of the number of available amine functions free to react with epoxy
groups in each O-MMT.
76
Following the addition of Fge, the Fge-grafted surfactants were characterized by MALDI-MS
analysis using DCTB-Ag as matrix. As Fge was added directly to the O-MMT clays, the surfactants
were thus in their protonated form and thus no longer able to react with DCTB (Chapter II, 2.3.3).
In consequence, in these experiments no CardSx – DCTB adduct were anymore expected. This
characterization allows to track the available amine content of the surfactants (means the free
primary and secondary amines), highlighted by the CardSx – Fge adducts potentially detected.
The resulting MALDI-MS spectra are depicted on Figure II - 19.
Figure II - 19. MALDI-MS spectra of Fge-grafted a) CardS1-MMT, b) CardS2-MMT, and c)
CardS3-MMT using DCTB-Ag as matrix.
Three additions of the Fge mono-epoxy on CardS1-MMT were readily detected: mono-addition at
m/z 655.5, di-addition at m/z 809.5, tri-addition at m/z 963.6) (Figure II – 19a). These results
were expected as f = 4 for CardS1. Indeed, because Fge only reacts with neutral amines, three
77
available amine functionalities (AAF = 3) are quantified for CardS1-MMT (CardS1 in its
protonated form within MMT).
Similarly, in the case of CardS2-MMT two additions of Fge were detected (AAF = 2) in Figure II –
19b, at m/z 569 (mono-addition) and m/z 723.6 (di-addition), as expected from protonated
CardS2 (f = 3).
For CardS3-MMT (Figure II – 19c) the protonated surfactant was readily detected at m/z 443.4
as the major product, indicating that the protonated CardS3 surfactant within MMT was not able
to react with Fge. However, a unique addition of Fge is surprisingly detected at m/z 597. This
addition of Fge was not expected from the CardS3 composed of a secondary and a tertiary amine
(f =1). Indeed, the protonated surfactant should not be able to react anymore as the protonation
is known to preferably occur on secondary amines (more basic than primary amines).
Nevertheless, the low abundance of this peak revealed the very poor reactivity of CardS3 towards
Fge. The mono-addition product of Fge on CardS3-MMT could be explained by the reactivity of
the secondary amine towards Fge in its neutral form, influencing the protonation equilibrium.
In conclusion, CardS3-MMT seemed not to be able to react with epoxy groups because the
protonated CardS3 specie was in majority detected. A higher reactivity towards Fge was observed
for the CardS2-MMT and CardS1-MMT samples, as the protonated surfactants were no longer
detected in the associated MALDI-MS spectra (expected at m/z 415 and 501 respectively). Indeed,
the detection of the Fge-grafted surfactants within O-MMT clay by MALDI-MS analysis confirmed
that the synthetized CardS1 and CardS2 surfactants contained available amine functionalities free
to react towards epoxy after the organomodification procedure. Furthermore, the expected
difference of the surfactants reactivity related to their amine content and nature could also be
observed. Indeed, the protonated CardS1 compound (f = 4) was able to react three times with Fge,
and protonated CardS2 (f = 3) reacted two times with Fge. As expected, the CardS3 compound (f
= 1) reacted almost not with Fge. The surfactants could thus be classified according to their
available amine functionalities (AAF) able to further react with epoxy after organomodification:
CardS1 (AAF = 3) > CardS2 (AAF = 2) > CardS3 (AAF <1).
2.5 Preparation and characterization of CPN materials
2.5.1 CPN preparation procedure
Clay mineral-based polymer nanocomposite (CPN) with conventional diglycidyl ether of
Bisphenol A (BADGE) were prepared to validate the impact of the available amine functionalities
of surfactants onto the MMT exfoliation. It is worthy to remind that the CPN with MMT or O-MMT
78
were prepared thanks to a simple magnetic stirring without any additional dispersion or
exfoliation enhancement.
Composite materials, composed of BADGE epoxy cured by diaminocyclohexane (DAC) and
including 10 wt% of O-MMT organomodified by CardS1, CardS2 or CardS3, were elaborated and
their morphology as well as their properties were investigated. A 10 wt% pristine MMT/BADGE
composite was also prepared as a reference.
2.5.2 CPN characterization by X-ray diffraction (XRD)
The effect of the MMT organomodification on the interlayer space between the clay platelets was
previously characterized. The interlayer distance was shown to increase from 12.6 Å (pristine
MMT) to around 20 Å regardless to the used surfactant.
In the following part, the relationship between amino-functionnalities of the surfactant reactive
towards epoxy within the clay and their effect on the MMT clay intercalation or exfoliation within
the BADGE polymer matrix were studied. To this aim, the composite materials were characterized
by XRD analysis.
X-ray diffractograms of the CPN are reported on Figure II – 20. First of all, it can be noted that a
diffraction peak from 2θ = 10 ° to 2θ = 20 °, due to BADGE, was observed in each diffractogram of
CPN materials.
Figure II - 20. X-ray diffractograms of CPN prepared with 10 mass% of pristine and
organomodified MMT by CardS1, CardS2 and CardS3.
79
For the reference pristine MMT/DEGBA CPN, the MMT diffraction peak was located around 6 °,
corresponding to a 15 Å interlayer distance between the MMT clay platelets and indicating that
the clay was not exfoliated. Furthermore, the XRD analysis of the raw MMT (Chap. II – 2.3.2)
indicated an interlayer distance of 12.6 Å. It can be concluded that the epoxy polymer barely
intercalated the pristine MMT.
In the case of the diffractograms corresponding to O-MMT/BADGE CPNs, a clear trend appeared
concerning the MMT clay dispersion state. Indeed, in the case of CardS3 (AAF < 1), a clear
intercalated structure was obtained with a diffraction peak at 3.2 ° (corresponding to an
interlayer length of 28 Å) in comparison to CardS3-MMT (2θ = 4.5 °, dCardS3-MMT = 19.6 Å). The shift
of the diffraction peak to lower angles indicated that the monomers were able to diffuse within
the clay platelets. However, because the CardS3 surfactant did not present enough available
amine functionalities to allow its reaction with the epoxy matrix the exfoliation of platelets during
polymerization did not occur.
When CardS2 was used to organo-modify MMT (with an expected AAF of 2), a partially exfoliated
structure was observed as depicted by the shoulder located around 2.2 ° (d = 40 Å). The clay was
partially exfoliated within the epoxy matrix and some intercalated clay aggregates were still
present. Finally, when CardS1 (with an expected AAF of 3) was used, no diffraction peak was
observed above 2 ° indicating that an exfoliated state tended to be reached.
The effect of the reactivity – i.e. the amine available functionality content - of the surfactants on
the exfoliation of clay within an epoxy polymer matrix was demonstrated. The clay
organomodification by the surfactant with the higher available amine functionnalities (CardS1,
AAF = 3) led to an exfoliated state, whereas the surfactants with lower AAF resulted in partially
exfoliated or intercalated states (CardS2 (AAF = 2) and CardS3 (AAF < 1) respectively).
2.5.3 CPN Thermal characterisation
DSC characterization of BADGE/O-MMT CPN materials elaborated with MMT clay
organomodified by the most reactive surfactant CardS1 was carried out with the aim to determine
the effect of the clay exfoliation on the final materials thermal properties.
In a first time, the epoxy thermoset BADGE cured with 1,2-diaminocyclohexane (DAC) in
stoichiometric proportions was prepared as a reference (BADGE/DAC). Then, epoxy
nanocomposite materials with various amount of MMT were prepared. BADGE/MMT
nanocomposite materials were elaborated with 5 %, 7% or 10 % of pristine MMT, labeled
hereafter CPN5%, CPN7% and CPN10% respectively. The effect of the BADGE/ MMT ratio was
then investigated by the DSC analysis (Figure II – 21).
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Figure II - 21. DSC thermograms of BADGE/DAC and CPN prepared with 5, 7, and 10 wt% of
pristine MMT.
As observed by XRD analysis on Figure II - 17, materials elaborated from BADGE and pristine
MMT led to composite materials where the dispersed MMT clay was aggregated. Indeed, the MMT
diffraction peak around 6 ° was readily observed, indicating that the MMT was not intercalated
or exfoliated within the elaborated epoxy materials. Nevertheless, as it could be observed on the
DSC thermograms displayed on Figure II - 21, the addition of pristine MMT to BADGE/DAC epoxy
thermoset allowed an increase of the materials Tg. It was shifted from 170 °C for the BADGE/DAC
reference to 200 °C for CPN7% and CPN10% and to Tg = 205 °C for CPN5%. The classical polymer-
inorganic filler interaction must be responsible for this polymer chain mobility hampering and so
the Tg increased.114
In the same way, BADGE/O-MMT (modified by CardS1) nanocomposite materials were
elaborated with 5 %, 7 % or 10 % of CardS1-MMT, labeled hereafter CPN-OMMT5%, CPN-
OMMT7% and CPN-OMMT10% respectively. The corresponding DSC thermograms are displayed
in Figure II - 22.
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Figure II - 22. DSC thermograms of BADGE/DAC and CPN prepared with 5, 7, and 10 wt% of
MMT modified by CardS1.
The surfactant CardS1 was demonstrated to be the most reactive surfactant towards the BADGE
epoxy leading to an exfoliated structure of the O-MMT clay within the epoxy matrix. The
nanocomposite structure of those materials was confirmed by the absence of MMT diffraction
peak on the XRD diffractogram (Figure II – 20). The thermal properties of the CPN-OMMT5%,
CPN-OMMT7% and CPN-OMMT10% nanocomposite materials were thus expected to be different
from their counterpart composite based on aggregated MMT. Despite an exfoliated structure of
the O-MMT clay, the Tg of the nanocomposite materials were found to decrease when compared
to the materials with pristine MMT clay. Indeed, the measured Tg were decreasing from Tg = 170
°C for the BADGE/DAC to Tg = 165 °C, 150 °C and 130 °C for CPN-OMMT5%, CPN-OMMT7% and
CPN-OMMT10%, respectively. The Tg are decreasing with increasing amount of O-MMT, and thus
increasing amount of cardanol-based surfactant. As the MMT is modified by a cardanol-based
surfactant, this effect may be attributed to a predominating plasticizing effect induced by the
cardanol alkyl side chain. This phenomenon could furthermore be attributed to
homopolymerization of the epoxy monomers triggered by the presence of cationic compounds,
decreasing thus the materials crosslinking density. Indeed, for the material elaborated with
pristine MMT, the materials Tg were observed to increase with the presence of pristine MMT (Tg
= 170 ° C for BADGE/DAC and Tg = 205°C, 200 °C, 200 °C for CPN5%, CPN7% and CPN10%,
respectively), despite the aggregate state of the pristine MMT clay within the epoxy matrix.
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2.5.4 CPN characterization by SEM and EDX analyses
Morphological observations with scanning electron microscopy (SEM) were performed to
confirm XRD analyses about the extent of the clay exfoliation in the polymer matrix. The use of
the most reactive surfactant CardS1 for the clay organomodification was shown to result in
exfoliated clay within the BADGE epoxy matrix. On the contrary, an intercalated structure was
achieved for the materials obtained from the clay modified with the less reactive surfactant
CardS3. In order to compare the two structures, the SEM analyses were performed on the
BADGE/CardS1-MMT CPN and BADGE/CardS3-MMT CPN materials. On Figure II - 23 are
reported a) topographic micrographs, b) chemical contrast micrographs and c) aluminium
mapping of MMT-CardS3 (above pictures) and MMT-CardS1 (bottom pictures) CPN. As a
reminder, MMT contains aluminum oxide in its crystal structure. SEM images were recorded on
fractured samples.
Figure II - 23. I) Scanning electron micrographs of the fracture of MMT-CardS3 (above part)
and MMT-CardS1 (bottom part) based CPN. a) corresponds to the topographic micrographs, b)
to the chemical contrast (BSE detector, the lightest the points and the heaviest the elements)
and c) is the aluminium distribution of the analysed area
II) Element composition obtained for analyses of an aggregate (EDS1) and unfilled area (EDS2).
(EDS3) corresponds to the homogeneous area
83
In the case of CardS3 based CPN, large aggregates (several tenth µm) were visible on the
topographic micrographs (Figure II – 23a, above part). Local energy dispersive X-Ray analyses
(EDX) measurements were carried out in order to identify the aggregates (Figure II – 23b, above
part, EDS1). The aluminum distribution (Figure II – 23c, above part) and the local EDS
measurements clearly evidenced that the aggregates were mainly composed of Al, main
components of alumino-silicate clay minerals. EDX measurements performed on areas without
aggregates (Figure II – 23b, above part, EDS2) were mainly composed of C and O, corresponding
to the chemical composition of the epoxy matrix.
In the case of the CardS1-based CPN (Figure II – 23a, bottom part), a homogeneous structure
was observed. Aluminum mapping (Figure II – 23c, bottom part) indicated that the element was
uniformly distributed all over the surface of the observed fracture. Whatever the part analyzed
by EDX, a similar composition was observed (an example is reported on Figure II – 23b, bottom
part, EDS3).
SEM/EDX analyses were in good adequacy with XRD measurements: the use of the less reactive
surfactant CardS3 resulted in composite materials with clay aggregates within the polymer
matrix, and no trace of exfoliated clay (no trace of Al) was found in the areas free of aggregates.
On the contrary, the use of the most reactive surfactant CardS1, with high amino group content,
led to an exfoliation of platelets-like clay minerals in epoxy, as the Si and Al compounds were
homogeneously present within the BADGE/CardS1-MMT material.
3 Conclusions
This study dealt with the synthesis of three bio-based surfactants and the comparison of their
different reactivity on the dispersion of MMT in epoxy. The surfactants were synthesized from a
glycidyl ether derivative of cardanol, a C15-alkylphenol. Three amines were used to modify the
cardanol-issued molecule, differing by the number of available amine groups Tris(2-
aminoethyl)amine (TAEA), ethylene diamine (EDA) and N,N-dimethylethylenediamine
(DMEDA), yielding to surfactants with different amount of reactive functionalities towards epoxy.
CardS1 synthetized from NC-513 and TAEA has an amine functionality of 4 (f = 4) as evidenced
by the formations of 4 adducts with DCTB observed by MALDI-MS characterization. Similarly,
CardS2, the product of the reaction between NC-513 and EDA, was shown to have 3 reactive
amine functionalities (f = 3), and CardS3 synthetized from EDA and NC-513 showed the lower
amine functionality content with f = 1.
X-ray diffractograms and MALDI-TOF/MS were used to evidence the success of the
organomodification as the interlayer space was demonstrated to increase with the presence of
the cardanol-based surfactants. Nevertheless, due to their close chemical structure, the uses of
84
the three cardanol-based surfactants led to roughly the same interlayer distance between the
platelets.
In sum, a deeper clay exfoliation was expected during epoxy-amine polymerization process giving
the nanocomposite material at the end. That is why the available amine functionality content of
each surfactant, once situated within the MMT clay, was investigated. Indeed, as it could be
observed by MALDI-MS analysis, the surfactants seemed to display a different reactivity
according to their environment (without or within the clay platelets). To verify the available
amine functionality content of the surfactants within the clay, furfuryl glycidy ether (Fge)
compound was grafted to the surfactants, and the Fge-grafted surfactants were detected by
MALDI-MS characterization. As expected, more Fge units were grafted to the surfactants with
higher amino group content. Nevertheless, available amine functionality (AAF) of the surfactants
within the clay were found to be lower than those of the neat surfactants: CardS1 (AAF = 3) >
CardS2 (AAF = 2) > CardS3 (AAF < 1). Clay mineral-based polymer (CPN) with conventional
diglycidyl ether of bisphenol A were then prepared with the three O-MMT.
Lower glass transition temperatures than for the reference BADGE/DAC materials were observed
when O-MMT modified by CardS1 was added. Indeed, the addition of MMT clay modified by
cardanol-based surfactants seemed to lower the materials properties due to the plasticizing effect
of the cardanol alkyl side chain and homopolymerization of the epoxy monomers induced by the
presence of cationic species. Still, the introduction of O-MMT clay modified by cardanol-based
surfactants may be an innovative way to increase the flexibility of some brittle thermosets such
as polybenzoxazines.
Finally, it was concluded thanks to XRD and SEM analyses coupled with energy dispersive X-ray
analyses that the reactivity of the surfactants led to an enhancement of the dispersion of MMT
platelets. No diffraction peak was observed by XRD when the most reactive surfactant (CardS1)
was used to modify MMT, while a clear intercalated structure was evidenced for the surfactants
with the lowest amino group content (CardS2 and CardS3). Similarly, SEM/EDX evidenced a
better dispersion of O-MMT platelet when using CardS1. This cardanol-based surfactant was thus
efficient for promoting both ion exchange and exfoliation of the clay platelets; it is thus a good
candidate for Montmorillonite clays dispersion.
The efficiency of the synthetized cardanol-based surfactants on the clay exfoliation on a
Bisphenol-A based epoxy matrix was highlighted in this work. The approach of modifying MMT
clay by a bio-based surfactant could further be applied to bio-based epoxy matrices in order to
lower the carbon footprint of the materials and to tend to the elaboration of fully bio-based high
performance materials.
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Chapter III: Benzoxazines from cardanol
1 Introduction
Benzoxazines (Bz) gained a great interest due to their huge potential to overcome several short-
coming of conventional novolac and resole-type phenolic resins while keeping clear assets. Di-
functional benzoxazines (di-Bz) are widely studied since the last two decades and the growing
number of new benzoxazine (Bz) structures attest the clear benefit that represents its versatile
chemical design. Indeed, the versatility in the chemical structure of Bz monomers comes from
large variety of phenolic and amino-based compounds available. With the growing trend to
producing environmentally-friendly and high performance materials derived from renewable
resources, the use of bio-based phenolic derivatives for the synthesis of Bz monomers is
considered as a viable alternative to petroleum-based phenolic counterparts. Under this trend,
several reports have studied the use of bio-based phenolic compounds such as cardanol, vanillin,
eugenol, etc.… for the synthesis of mono- or di-functional Bz monomers. Nevertheless, the
processability (melting and shaping) of these monomers remains generally difficult due to too
close melting and polymerization temperatures. An interesting approach for acting on the Bz
monomers processing windows consists in the versatile synthesis of asymmetric di-Bz
monomers using for example a diamine as bridging group between cardanol and a second
phenolic derivative. It yields in a lowering of the melting temperature in comparison to the
symmetric monomers. This proposal is expounded in this chapter.
1.1 Benzoxazine thermosets
1.1.1 Generalities
Thermoset polymers are mainly represented by phenolic, epoxy or bismaleimide resins. These
polymers are well known for their high performance applications due to notable thermal and
mechanical properties, good chemical resistance and flame retardation. However, these high
performance multicomponent thermosets suffer from significant shortcomings such as high
brittleness as well as the formation of voids and by-products during curing. Benzoxazine resins –
namely polybenzoxazines (PBz) – are a new class of thermoset polymers emerging since several
decades and are considered as a promising substitution of phenolic or epoxy resins. Indeed, in
addition to properties similar to those of phenolic or epoxy resins,115, 116 PBz are also
characterized by low water absorption,115 high char yield116 and near-zero volumetric shrinkage
or expansion during polymerization.117, 118 Benzoxazine monomers are synthesized through a
86
Mannich-like condensation of a phenolic derivative, a primary amine (aliphatic or aromatic) and
formaldehyde, followed by a ring-closure process (Figure III - 1).81, 119
Figure III - 1. Classical two-step approach for the synthesis of mono-benzoxazine monomers.120
Mono-benzoxazine monomers (m-Bz) are gathering the monomers composed of one benzoxazine
group, in opposition to di-benzoxazine monomers (di-Bz), composed of at least two benzoxazine
moieties (Figure III - 2). Di-Bz monomers can be synthetized from various starting reagents,
either from a diphenolic compound (1eq) with a primary amine (NH2-R) (2eq) and
paraformaldehyde (4eq), or from a diamine compound (NH2-R-NH2) (1eq) with a phenol
derivative (2 eq) and paraformaldehyde (4 eq).
Figure III - 2. Chemical structure of a) mono-benzoxazine (m-Bz) and b) di-benzoxazine (di-Bz)
monomers.
87
1.1.2 Benzoxazine polymerization
Polymerization of Bz monomers – generally 1,3-benzoxazine isomers121 – is achieved by
thermally-induced auto-catalysed ring-opening polymerization (ROP) (Figure III – 3), avoiding
therefore the use of strong acid catalysts and/or the formation of by-products.118
Figure III - 3. Thermally-induced ring opening polymerization of Bz monomers.120
Thus PBz resins are advantageously mono-component resins, compared to phenolic or epoxy
resins. Indeed, Bz ROP occurs without the use of catalyst in a temperature frame of 160 °C to 220
°C. Bz monomers contain a small amount of impurities such as phenolic raw materials and
oligomers, allowing the initiation of the polymerization as the temperature arise. The
polymerization is then auto-catalysed by the formation of phenolic compounds through the
monomer ring-opening.118
Depending on the structural nature of the Bz monomers, either linear or cross-linked polymers
are obtained. It has been shown that Bz monomer polymerization preferentially occurs at the
ortho position of the hydroxyl function (Figure III – 3).119, 122, 123 Polymerization of m-Bz typically
leads to low weight linear polymers around a few hundreds to a few thousands g/mol.123
Especially for m-Bz monomers from para-substituted phenolic compounds, it was demonstrated
that the polymerization was self-terminated after a single ring-opening. Indeed, the
polymerization was stopped at a dimer level by the formation of a six-membered ring between
the aza-methylene and the hydroxyl group of the phenolic ring (Figure III - 4).124, 125
88
Figure III - 4. Dimer product of para-substituted m-Bz monomer via ring-opening reaction.124
However, if the m-Bz phenolic ring is reactive enough, meaning additional polymerization
positions such as para positions are available, even m-Bz monomers could lead to cross-linked
PBz.120 Indeed, if the para and/or meta positions are available, they may also react in the
polymerization process. The reactivity reduces from ortho to para and from para to meta, which
is rather unreactive (Figure III - 5).120
Figure III - 5. Possible polymerization reactions sites in order the most to the least
predominant: 1 ortho, 2 para, 3 meta.120
Nevertheless, PBz from m-Bz monomers are usually low molecular weight materials due to
competition between thermal dissociation of the monomers and the chain propagation as
demonstrated by Reiss et al..123 On the contrary, di- or poly-functional Bz monomers lead almost
systematically to infinite molecular weight cross-linked polymers due to their higher
functionality.126, 127 The use of di-Bz monomers for the elaboration of high performance materials
is in consequence widely preferred to m-Bz monomers.
89
1.1.3 Effect of hydrogen bonding and π-π supramolecular interactions on polybenzoxazines
properties
Excellent properties were reported for PBz resins. Nevertheless Ishida et al.115 reported that,
despite displaying high Tg’s and high moduli, the crosslinking density of PBz resins remained very
low in comparison to epoxy resins. Generally, high glass transition temperature is in correlation
with the high crosslinking density. Wirasate et al.128 studied the dependency of various hydrogen-
bonding infrared modes to understand the hydrogen-bonded structure in the PBz resins. They
reported two types of hydrogen bonds within PBz materials. Both statistically distributed and
conformationally preferred hydrogen bonding may contribute to the stiffness of the system and
led to high Tg and high modulus polymer. The excellent properties of PBz resins have further been
attributed to the hydrogen bonds within the materials by several other studies.129-133
The reinforcement strategy of PBz resins generally relies on extensively used polymer fillers as
polyhedral oligomeric silesquioxanes (POSS),134-136 clay minerals,137-141 or carbon nanotubes.142-
146 Recent works on carbon nanotubes (CNT)/polybenzoxazines composites raised interests onto
convenient composites preparations based on π-π supramolecular interactions leading to good
reinforcement of the PBz materials.142, 143, 146 Nevertheless, the thermo-mechanical properties of
PBz/CNT composite materials were moderate and strongly dependent on the functionalization of
the CNTs fillers.136 Dumas et al.143 proposed the elaboration of PBz/CNT nanocomposites with
good thermo-mechanical properties through the facile and efficient dispersion of neat CNTs
within various Bz compounds: M1 (Bisphenol A/aniline based Bz monomer) and M2 (1,4-
phenylene diamine/phenol based Bz monomer) (Figure III - 6).
Figure III - 6. Chemical structures of the Bz monomers used for the elaboration of Bz/CNT
nanocomposites.143 – M1: Bisphenol A/aniline based Bz monomer and M2: 1,4-phenylene
diamine/phenol based Bz monomer.
For nanocomposite compounds containing 5 wt% of CNTs, the Tg and storage modulus of M1-
based PBz material remained unchanged, whereas a significant improvement was observed for
M2-based PBz materials. Indeed, the Tg of the M2-based PBz material was shifted by 50 °C to
90
higher temperatures, and the onset of its thermal degradation was shifted from 250 °C to 300 °C.
These results were correlated to strong supramolecular filler-matrix π-π interactions.
Regarding clay minerals, a traditional organomodification approach is employed to promote clay
dispersion in Bz. As defined in the previous chapter, this strategy relies on the exchange of the
clay inter-platelets cations by a reactive and organophilic cation to enhance the diffusion of Bz
monomers within the clay platelets galleries and therefore favouring the polymer growing to
reach an exfoliated state. 140, 141, 147, 148 Conscious of the strong interactions driving the properties
of PBz networks, it appears clear that using supramolecular interactions for the reinforcement of
PBz matrix is a facile and efficient strategy.
Motivated by these approaches and in order to study the interaction between pristine clay and
PBz resins, prior to clay organomodification, we proposed to study the supramolecular
interaction between kaolin and poly(EDBz).149 Indeed, kaolin is a common raw material which
main component is kaolinite, a 1:1 clay mineral composed of single layers with a SiO4 tetrahedral
network connected to Al(O, OH)6 octahedral networks with platy particle of hexagonal symmetry.
The layers are held together via hydrogen bonds, dipolar interactions and attractive Van der
Waals forces, which results in a low intrinsic inner surface reactivity. Isomorphic substitutions
within the layers generate negative charges that are counterbalanced by alkali cations (Na+ and
K+) situated at the interlayer. Such cations are known to catalyse Bz crosslinking reactions.150
Thus, due to its intrinsic interactions, kaolin appears as an adequate candidate to form
supramolecular assembly with Bz. Composite materials, containing 10 wt% of neat kaolin, were
elaborated. The FTIR measurements attested of the establishment of supramolecular H-bonding
interactions between EDBz and kaolin in the monomer melt, leading to fine clay dispersion into
the resin after polymerization, as evidenced by SEM analyses (Figure III - 7).
Figure III - 7. Representative SEM images of a) pristine kaolin and b) 10 wt% kaolin/EDBz.
Thanks to the promoted dispersion of kaolin driven by the H-bonding interactions, the thermal
and thermo-mechanical properties of the benzoxazine resins were significantly improved. For
instance, increases of the Tg from 161 °C to 171 °C, of the storage modulus from 3.4 GPa to 4.9
91
GPa and the thermal stability from 220 °C to 245 °C were triggered by the incorporation of 10
wt% of kaolin. The completed study is not detailed in this manuscript, please report to Ganfoud
et al.149 for additional information.
1.1.4 Polymerization catalysis
Even though the polymerization of benzoxazine monomers is thermally activated and auto-
catalysed by the formation of new phenolic compounds through the ring opening polymerization,
some initiators/catalysts may be added to trigger the polymerization of Bz monomers at lower
temperature.151-155 Wang et al.151 achieved a screening of the use of possible initiators and/or
catalysts for reducing the curing temperature and curing time of Bisphenol A/aniline - based Bz
monomers (BA-a). The polymerization of (BA-a) monomers with 5 mol% of various catalysts was
carried out at 20 °C during 20 h. The thermal properties of the Bz monomers cured in presence
of effective catalyst were investigated and compared to the properties of the thermally cured neat
(BA-a) material (Tg = 177 °C, Char yield = 30 %). It was observed that the use of some catalysts
for the polymerization resulted in materials with higher Tg and higher char yield. Particularly
when Lewis acids such as PCl5, PCl3, POCl3 and TiCl4 were used, Tg’s higher than 200 °C were
recorded. Furthermore, char yields around 50 % were recovered from TGA analysis. The use of
catalysts could thus be interesting for the elaboration of thermal protection materials. In
conclusion a broad variety of catalysts may be used for the ring opening polymerization of Bz
monomers at lower temperature.
Beside their effective catalyst activity, the majority of the catalysts appear to be petroleum-based
and/or toxic. MgCl2 and ZnCl2 were evaluated as a safer alternative and as new catalysts to reduce
the polymerization temperature of a (cardanol/aniline)-based Bz monomers, which usually
polymerize at elevated temperature (around 260 °C).156 As it can be observed in Table III - 1, the
use of 1 mol% of these catalysts enabled to significantly reduce the polymerization temperature,
even below 200 °C in the case of MgCl2.
Catalyst Polymerization
temperature (°C)
No catalyst 260.6
MgCl2 193.1
ZnCl2 207.1
p-TsOH 206.0
Table III - 1. Polymerization temperatures of (cardanol/aniline) PBz cured with 1 mol%
catalyst.156
92
Some researchers studied also the ring opening catalysis of Bz monomers by the addition of
catalytic functional groups on the monomers such as carboxylic acids.157, 158 Andreu et al.158
analysed the thermal polymerization behaviour of several carboxylic-containing Bz monomers
(Figure III - 8), and studied their effect on the polymerization temperature when used as co-
monomer with a (phenol/aniline) monomer (m1). The thermal properties of the different Bz
monomers are in Figure III - 8.
Figure III - 8. Chemical structure and thermal properties of Bz monomers containing carboxylic
groups.158
As it can be seen in Table III - 2, small amounts of monocarboxylic monomer induced a reduction
of about 20 to 30 °C of the polymerization temperature which was even more important when
the amount of carboxylic-containing co-monomer increased. For over 25 % of co-monomer
amount, the polymerization temperatures were even lower than for m2 or m3 alone. In
comparison, mixtures with dicarboxylic monomer m4 were reported to have a stronger catalytic
effect. Indeed, with 5 % of m4, the temperature of copolymerization with m1 was decreased by
50 °C. When comparing the Tg of the copolymer PBz materials, it could be observed that materials
obtained from carboxylic-containing Bz monomers tended to have higher Tgs than m1 based PBz
materials. These results were most probably due to higher crosslinking due to hydrogen bonding
with increasing content of cardboxylic acid functions.
93
Co-monomer % co-monomer Polymerization
temperature (°C) Tg (°C)
Reference :
m1 alone - 262 111
m1 + m2 5 238 121
m1 + m2 50 178 107
m1 + m3 5 232 120
m1 + m3 50 187 146
m1 + m4 5 215 128
m1 + m4 50 192 158
Table III - 2. Thermal properties Bz materials from reaction between m1 and carboxylic-
containing Bz co-monomers m2, m3, and m4. 158
1.1.5 Focus on di-benzoxazine monomers
Di-functional Bz monomers are favoured for the elaboration of high performance PBz materials.
They are divided in two classes, depending on whether they are prepared from a di-phenol (Class
A) or a diamine (Class B). These two classes are schematized in Figure III - 9.
Figure III - 9. Chemical structures of Class A and Class B di-Bz monomers.
The structure-to-properties relationship is similar for Class A and Class B di-Bzs. The rigidity or
the electronic state of the bridging group has a similar impact. Nevertheless, class B di-Bz
monomers, i.e. phenols bridged with a diamine, are of major interest owing to their versatile
synthesis and the numerous mono-phenolic and diamine reagents available. Nevertheless, the
nature of the diamine bridging group is strongly affecting the synthesis conditions and the
thermal properties of Bz monomers and corresponding PBz resins.159-161 162-164 Furthermore, the
nature of the substitution of the phenolic compound drives particular functionality of the Bz
monomers,159, 165-167 such as functional groups promoting the thermal activation of the ROP or
increasing the crosslinking density of the resulting PBz materials.
In the coming paragraphs, we will only focus on the state-of-the art on Class B di-Bzs as they are
the main focus of the work presented in this chapter. For more details, a full description is given
in [Pierre Verge, Laura Puchot, Cédric Vancaeyzeele, Frédéric Vidal, Youssef Habibi, "Symmetric vs
94
asymmetric di-Bz monomer design: structure-to-properties relationship" in "Advanced and
Emerging Polybenzoxazine Science and Technology," Ishida, H.; Froimowicz, P. Eds. Elsevier,
Amsterdam (2016).]
1.2 Synthesis of Class B benzoxazines
The synthesis of class B di-Bz monomers is determined by the nature and origin of each reagent
while the synthesis conditions and yields are strongly affected by the electron donating and
withdrawing effects as well as by the length of the diamine bridging group (Figure III - 10).
Figure III - 10. Chemical structure of Class B di-Bz monomer.
1.2.1 Electron donating and withdrawing effect
The nature of the bridging group represents one of the main factors affecting the ring-closing
reaction of the Bz oxazine rings (Figure III - 1). The influence of electron donating or withdrawing
effects of different bisphenol bridging groups on the Bz ring closure were previously
investigated.168 It was evidenced that the electron donating effect of bridging groups such as –
CH2 or a single bond promotes the formation of the Bz oxazine ring. On the contrary, the
withdrawing effect of bridging groups such as –CO or –SO2 stabilizes the mesomeric form of the
phenolic groups, and thus decreases the capacity of bisphenol to close the oxazine ring. Similarly,
the electronic effect of the diamine bridging group is also affecting the oxazine ring synthesis.
Indeed, the basicity of the primary amines is an important factor for the Bz monomer synthesis.169
Hence, an electron withdrawing effect of the diamine bridging group will tend to lower the amino
group basicity, impeding the Bz oxazine ring closure. On the contrary, electron donating effects
of the diamine bridging group will enhance the basicity of the primary amino groups, promoting
the Bz oxazine ring formation.
1.2.2 Flexibility of the bridging diamine
The flexibility of aliphatic diamines is also impacting the reaction conditions of the monomers
synthesis. The effect of the chain length of aliphatic diamines as bridging groups was
95
investigated.162 The reaction times of the Bz monomer synthesis with increasing diamine chain
length, from short and relatively rigid ethylenediamine to long and relatively flexible 1,12-
diaminooctane, are listed in Table III - 3.
Monomer Diamine Reaction Time (h)
P-ad2 H2N-(CH2)2-NH2
Ethylene diamine 1.5
P-ad4 H2N-(CH2)4-NH2
1,4-diaminobutane 4
P-ad6 H2N-(CH2)6-NH2
1,6-hexane diamine 8
P-ad8 H2N-(CH2)8-NH2
1,8-diaminooctane 10
P-ad12 H2N-(CH2)12-NH2
1,12-diaminododecane 12
Table III - 3. Reaction times of synthesis of Bz monomers in CHCl3 at reflux with increasing
diamine chain length.162
It was evidenced that a short length diamine allowed a faster and easier monomer formation than
a long chain diamine.162 As it can be seen in Table III - 3, the reaction times were shifting from
1.5 h to 12 h while increasing the diamine chain length from 2 to 12 carbons. Low reaction times
are thus favoured by short length diamine bridging groups such as ethylenediamine.
1.3 Thermal properties of Class B di-Bz monomers and PBz resins
As related by numerous studies, the flexibility and chain length of the diamine bridging groups
are largely determining the thermal properties of the di-Bz monomers and their corresponding
PBz materials.
1.3.1 Flexibility and chain length of the bridging diamine
As PBz resins are mainly intended for high performance applications, aromatic diamines that
stand as rigid bridge have been widely used for the design of di-functional Bz monomers,
hereafter known as aromatic-di-Bz. These rigid bridging groups, inspired from the development
of epoxy-based thermoset materials, are largely preferred for the synthesis of high glass
transition temperature (Tg) materials. The thermal properties of model aromatic-di-Bz
monomers, synthetized from aromatic diamines and phenols, and those of their corresponding
PBz materials are listed in Table III - 4.
96
Bz monomer Tm
(°C)
Tp
(°C)
Tg
(°C) Ref.
1,4-phenylenediamine (pd)
- - 260 170
N,N diaminodiphenylmethane (ddm)
123 244 208 160
(4-aminophenyl)ether (dde)
- - 194 170
4,4’-diamino diphenyl sulfone (dds)
209 261 184 160
(4-(4-aminophenoxy)phenyl)ether (44appe)
164 239 172 160
2,2-bis(4-(4-aminophenoxy)naphthalene (ndpa)
152 249 170 160
Table III - 4. Melting point (Tm) and polymerization temperature (Tp) of model aromatic-di-Bz
monomers and Tg of their corresponding aromatic-PBz materials.
Materials with high Tg typically ranging from 170 °C to 260 °C were obtained with aromatic
diamines as bridging groups. Higher flexibility of the aromatic diamine backbone, for example in
the case of 44appe or ndpa, induced a lower Tg, 172 °C and 170 °C respectively, than for Bz with
more rigid aromatic diamine such as 1,4-phenylenediamine (Tg = 260 °C). However, the relatively
high melting temperatures of aromatic-di-Bz monomers (above 120 °C) complicate the materials
processing (molding and shaping), due to the short processing windows Tproc, defined as the
difference between the monomer melting temperature (Tm) and its polymerization temperature
(Tp).
97
The brittle nature of aromatic PBz materials has led researchers to consider aliphatic diamines
as flexible bridging group to design Bz monomers, hereafter known as aliphatic-di-Bz. The
thermal properties of model aliphatic-di-Bz monomers, synthetized from various chain length
linear diamines and phenol, and their corresponding aliphatic-PBz materials are listed in Table
III - 5.
Bz monomer Tm (°C) Tp (°C) Tg (°C) Ref.
Ethylene diamine
112 185 179 162
1,4-diaminobutane
94 225 169 162
1,6-hexane diamine
83 225 171 162
1,8-diaminooctane
73 236 137 162
1,12-diaminododecane
49 241 105 162
Table III - 5. Thermal properties of aliphatic- di-Bz monomers, synthetized from various chain
length linear diamines and phenol, and Tg of their corresponding aliphatic-PBz materials.
The chain length of flexible linear diamine bridging groups is an essential parameter affecting the
thermal properties of the di-Bz monomers and their related PBz materials. The melting
temperatures of aliphatic Bz monomers were found to be significantly lower than those of
aromatic-di-Bz monomers (< 155 °C), while their polymerization temperatures remained in the
usual temperature range of 200-220 °C. Moreover, the melting temperatures of the aliphatic Bz
monomers were considerably decreased, from 112 °C to 49 °C, with increasing the diamine
bridging group chain length. Thus, the processing windows Tproc of aliphatic di-Bz monomers
were wider than for aromatic-di-Bz, from 73 °C to 192 °C with increasing the diamine chain
length. Furthermore, the glass transition temperatures (Tg) also decreased proportionally from
179 °C to 105 °C with increasing the diamine chain length.162
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In conclusion, the synthesis of aromatic-di-Bz monomers yielded to compounds with relatively
high melting temperatures, and to aromatic PBz with high Tg. On the contrary, flexible bridging
groups (aliphatic diamines) allowed the synthesis of low melting temperature aliphatic-di-Bz
monomers, with a wide processing window. Nevertheless, the higher flexibility of the aliphatic
bridging group impedes the Tg of the materials, underlining the difficulty to find a compromise
for the design of high performance materials with moderate processing conditions.
1.3.2 Additional functional groups
The introduction of some functional groups has been tentatively considered to promote lower
thermal activation or to improve the properties of the resultant PBz materials.
The effect of the allyl group of o-allylphenol on Bz monomers prepared with various diamines
was studied.159, 166, 165 However, despite a lowering of the polymerization activation temperature,
the presence of the allyl group on the phenolic ortho position hampered the polymerization
process of the benzoxazine, resulting in lowering the crosslinking density of the networks.
Maleimide functional groups, were shown to enhance the PBz materials thermal properties.167 A
set of di-Bz monomers was synthetized by bridging phenyl maleimides with various diamines
using xylene as high boiling point solvent (Figure III - 11). The ring-opening polymerization of
the phenyl maleimide-based Bz monomers, as well as the addition-polymerization of the
maleimide groups occurred in the same temperature range of traditional Bz monomers (Tp ~ 200
°C - 220 °C), while the resulting PBz materials exhibited high Tg (c.a. 300 °C) and excellent thermal
stability (T5% > 370 °C).
Figure III - 11. Synthesis of di-Bz monomers bearing maleimide functional groups. 167
In summary, class B di-Bz monomers are considered as the most appropriate and versatile
structures for the synthesis of novel high performance PBz materials. The choice of the diamine
99
strongly affects the synthesis conditions, yields, thermal properties and polymerization kinetics
of class B di-Bz monomers and of their corresponding PBz materials. First of all, a moderate/wide
processing window is important for the easy elaboration of PBz materials. As aromatic-di-Bz
monomers were characterized by high melting temperatures and narrow processing windows,
the use of an aliphatic diamine should be preferred for the synthesis of di-Bz monomers easier to
process due to their wide processing windows. Furthermore, even though the melting
temperature of Bz monomers decreased with increasing the aliphatic diamine chain length, their
Tg was clearly shifted to lower temperatures, lowering the thermo-mechanical properties of the
resulting PBz materials. In addition, the synthesis of Bz monomers with long aliphatic chains was
reported to be distinctly more difficult. As a result, short aliphatic diamine bridging groups, such
as ethylene diamine, should be preferred for the synthesis of di-Bz monomers displaying
moderate processing windows therefore resulting in high crosslinked PBz materials with good
thermal and mechanical properties.
1.4 Bio-based benzoxazine: State of the art
With the growing trend to produce environmentally-friendly and high performance materials
derived from renewable resources, the use of bio-based phenolic derivatives for the synthesis of
Bz monomers is considered as a viable alternative to petroleum-based phenolic counterparts. A
broad screening of various mono- or di-functional Bz monomers from naturally occurring
phenolic compounds, and their resulting materials have been reported during the last years,
attesting the clear trend of promoting the use of renewable bio-resourced reagents for the
development of competitive bio-based thermosets (Figure III - 12).
100
Figure III - 12. Example of naturally occurring phenolic derivatives used for the synthesis of
bio-based Bz monomers.
1.4.1 Vanillin
Vanillin is a phenolic compound with an ortho methoxy group and a para formyl group,
historically produced through extraction from vanilla seedpod but stems industrially mostly from
the processing of lignin.3, 171 Due to the high abundance of sustainable lignin resources,172, 173
vanillin appears as a promising substitute to oil-derived phenolic compounds or polymer
building-blocks.174-178 Its use as a precursor for the synthesis of bio-based Bz monomers was
recently studied.179, 180
The formyl group contained in the vanillin compound is of great interest for the synthesis of bio-
based Bz monomers. Indeed, with the appropriate stoichiometric amount of reagents and through
a convenient order of their introduction and reaction, the aldehyde function is not consumed
during the synthesis. This function is thus considered as an additional reactive group on the Bz
monomer, able to further react with other chemical compounds or to increase the material
crosslinking density.
The chemical structures as well as the thermal properties of vanillin-based Bz monomers and
their corresponding materials, reported in the literature, are summarized in Table III - 6.
101
Bz monomer Tm
(°C)
Tp
(°C)
Tg
(°C)
T5%
(°C) Ref.
1)
Vanillin/Aniline
83 231 - 347 179
2)
Vanillin/Furfurylamine
125 205 270 351 180
3)
Vanillin/Ethylene diamine
205 213 - 283 181
4)
Vanillin/4,4’-diamino diphenyl sulfone (dds)
229 277 255 339 181
5)
Vanillin/N,N diaminodiphenylmethane (ddm)
177 234 231 352 181
102
6)
Vanillin/ (4-aminophenyl)ether (dde)
145 234 227 322 181
7)
Vanillin/2,2-bis(4-(4-aminophenoxy)naphthalene
(ndpa)
- 228 202 488 181
Table III - 6. Thermal properties of vanillin-based Bz monomers, synthetized from mono-
functional amines or diamines, and Tg and T5% of their corresponding PBz materials.
It has been shown that the presence of the aldehyde group on vanillin has an immediate effect on
the thermal properties of the Bz monomer. Indeed, the presence of the formyl group on the
vanillin compound induces the formation of inter- and intra-molecular H bonds. Consequently, in
comparison to classical phenol-aniline Bz monomer, the melting temperature of vanillin-aniline
Bz monomer (Table III - 6, line 1) increased from 61 °C to 83 °C, whereas its polymerization
temperature decreased from 263 °C to 231 °C.179 The effect of inter- and intra-molecular H
bonding is further highlighted by the high melting temperatures of vanillin-based di-Bz
monomers. Indeed, the melting temperatures of the monomer reported in Table III – 6 were not
found to be lower than 145 °C (dde, Table III – 6, line 6), reaching even 229 °C for the di-Bz with
DDS as diamine (Table III – 6, line 4). These high melting temperatures, really close to the
polymerization temperatures are impeding the processing of these monomers (melting and
shaping). Nevertheless, vanillin-based Bz monomers led remarkably to cross-linked materials in
spite of substituted phenolic ortho and para positions, impeding the polymerization. It turns out
that the participation of the aldehyde group in the ring opening polymerization of the Bz
monomers has been previously reported.182 However, it was shown that the additional
crosslinking reactions, due to the presence of an aldehyde group within a Bz monomer, occur
mainly at the ortho position of the phenolic compound (Figure III - 13).
103
Figure III - 13. Schematization of the participation of the aldehyde group in the ring opening
polymerization of the para hydroxyl benzaldehyde Bz monomers.182
As the vanillin ortho position is blocked by a methoxy group, it can be assumed that the additional
crosslinking of vanillin-based Bz monomers is mainly caused by the decarboxylation of the formyl
group (Figure III - 14). Furthermore, some residual formyl groups, which did not undergo
decarboxylation, are forming inter-molecular H-bonding, further increasing the PBz crosslinking
density. Finally, the presence of the residual formyl groups is catalysing the Bz monomers ROP.182
181
Figure III - 14. Crosslinking of vanillin-based di-Bz monomers.181
In consequence, due to the presence of the aldehyde functions and thus to the formation of inter-
and intra-molecular H bonds, the vanillin-based materials were shown to display very high Tgs.
Indeed, vanillin-based di-Bz monomers resulted in PBz networks with Tg values reaching 255 °C
(DDS, Table III – 6, line 4). Nevertheless, di-vanillin Bz monomers are suffering from an evident
drawback: their short processing windows. Indeed, melting temperatures of di-vanillin Bz
monomers are too close from their polymerization temperatures, hindering their processing
(molding and shaping).181
104
1.4.2 Guaïacol
Guaïacol is another lignin-derivative phenolic compound, also studied as precursor for the design
of bio-based benzoxazine monomers.
Up to now, to the best of our knowledge, only mono-functional Bz monomers from guaïacol were
reported in the literature. The effect of two different bio-based primary amines on the thermal
properties of the monomer and corresponding PBz material were studied (Table III - 7). DSC
measurements revealed a Tg of 82 °C for a material obtained from the reaction between guaïacol
and stearylamine (Table III – 7, line 1). When furfurylamine was used for the synthesis of
guaïacol-based Bz monomer, an increase of the Tg to = 148 °C was reported (Table III – 7, line 2).
The authors did not give any information about the monomers melting points: the PBz materials
were shaped by solution casting of the monomers dissolved in acetone.
Bz monomer Tm (°C) Tp (°C) Tg (°C) T5% (°C) Ref.
1)
Guaïacol/Stearylamine
- - 82 329 183
2)
Guaïacol/Furfurylamine
- 240 148 352 183
Table III - 7. Thermal properties of guaïacol-based Bz monomers, synthetized from mono-
functional amines or diamines, and Tg and T5% of their corresponding PBz materials.
1.4.3 Lignin-derivatives
Among the lignin derivatives, coumaric (CA) and ferulic (FA) acids are present in relatively large
quantity in various plants as main components of lignocellulose.184 In addition, phloretic acid (PA)
is a phenolic compound obtained by hydrogenation of p-coumaric acid (Figure III - 15).
105
Figure III - 15. Chemical structure of lignin-derivative compounds: coumaric acid (CA), ferulic
acid (FE), and phloretic acid (PA).
These lignin-derivative compounds, as well as their methylated equivalents (CAM, FAM and PAM
respectively), were studied as precursor of mono-functional Bz monomers (Table III - 8). Bz
monomers with relatively high melting temperatures were obtained. Polymerization
temperatures of the Bz monomers were strongly affected by the carboxylic acid function. Indeed,
the carboxylic acid function acts as a polymerization catalyst, lowering the polymerization
temperatures compared to Bz with methylated functions. Thus, similarly to di-vanillin Bz
monomers, processing windows of Bz monomers with carboxylic acid function were low, due to
high melting temperatures (Tm = 117 °C and 121 °C for CA-Bz, FA-Bz) and low polymerization
temperatures (Tp = 137 °C and 130 °C respectively). The use of the methylated coumaric and
ferulic compounds allowed an increase of the processing window by increasing the
polymerization temperatures (processing windows = 107 °C and 37 °C respectively).
Furthermore, low thermal stability was reported for CA-Bz and FA-Bz, as well as for their
methylated derivatives CAM-Bz and FAM-Bz. Indeed, except for phloretic acid and methylated
phloretic acid based Bz monomers (PA-Bz and PAM-Bz), the polymerization proceeded with
partial decomposition, probably due to the presence of the conjugated double bond. This
phenomenon also impeded the preparation of suitable materials.
Bz monomer Tm (°C) Tp (°C) Tg (°C) T5% (°C) Ref.
1)
CA/aniline
117 137 119 220 184
106
2)
CAM/aniline
109 216 154 280 184
3)
FA/aniline
121 130 120 200 184
4)
FAM/aniline
166 203 135 135 184
5)
PA/aniline
122 212 130 130 184
6)
PAM/aniline
156 197 115 143 184
Table III - 8. Thermal properties of lignin-derivative-based Bz monomers, synthetized from
mono-functional amines or diamines, and Tg and T5% of their corresponding PBz materials.
107
1.4.4 Eugenol
Eugenol, through its availability and low cost, has also attracted attention for the synthesis of bio-
based Bz monomers. Eugenol is the main component (72 to 90 %) in the essential oil obtained
from cloves. It can also be extracted from other essential oils such as nutmeg, cinnamon, basil or
bay leaf oils. Eugenol chemical structure is a di-substituted phenolic compound by a methoxy and
an allyl group at ortho and para positions respectively. Consequently, due to blocked ortho and
para positions, only the low reactive meta positions are available, impeding the formation of a
cross-linked eugenol-based network (Figure III – 16).
Figure III - 16. Available positions for ring opening polymerization of eugenol-based Bz
monomer.
Furthermore, despite the allyl functional group on eugenol compound in para position, no
enhancement of the crosslinking density through homopolymerization of the resulting materials
was reported. Indeed, as the allyl group is attached to an aromatic structure, any formed radical
is stabilized by mesomeric effect, preventing free radical polymerization.185, 186 However, the
crosslinked materials from eugenol-based Bz monomers was obtained by using the allyl group as
a reactive function, and copolymerizing them with bismaleimides (Figure III - 17).187
Figure III - 17. Elaboration of crosslinked materials from eugenol-based Bz monomers by
copolymerization between allyl group and bismaleimides.187
108
As it can be observed in Table III - 9 m-Bz monomers from eugenol displayed large processing
windows but the Tg of the resulting materials, obtained from DSC, were relatively low (Tg = 101
°C and 148 °C for eugenol Bz monomers with stearylamine and furfurylamine respectively)
(Table III – 9, line 1 and 2).186 Similarly to di-Bz monomers from other naturally occurring
phenolic compounds, di-Bz monomers from eugenol and various aromatic diamines were all
displaying fairly high Tm > 90 °C, hampering also the elaboration of eugenol-based PBz
materials.188
Bz monomer Tm
(°C)
Tp
(°C)
Tg
(°C)
T5%
(°C) Ref.
1)
Eugenol/Stearylamine
49 218 101 313 186
2)
Eugenol/Furfurylamine
74 198 148 361 186
3)
Eugenol/ (4-(4-aminophenoxy)phenyl)ether
(44appe)
90 250 - 260 188
4)
Eugenol/1,4(bis(4’-aminophenoxy)phenyl sulfone)
(14apps)
100 250 - 275 188
5)
Eugenol/ (4-aminophenyl)ether (dde)
140 225 - 240 188
109
6)
Eugenol/4,4’-diamino diphenyl sulfone (dds)
130 255 - 295 188
7)
Eugenol/1,4-phenylene diamine
150 250 - 225 187
Table III - 9. Thermal properties of eugenol-based Bz monomers, synthetized from mono-
functional amines or diamines, and Tg and T5% of their corresponding PBz materials.
1.4.5 Coumarin
Coumarin was also studied as bio-resourced reagent for the synthesis of bio-based Bz monomers.
The specific coumarin compounds bearing a hydroxyl group in position 7 are of particular
interest for the synthesis of bio-based Bz monomers. Several studies reported the synthesis of Bz
coumarin monomers either from umbeliferone (Figure III - 18a) or from 4-methylumbeliferone
(Figure III - 18b) coumarin compounds. Their properties are reported in Table III - 10.
Figure III - 18. Chemical structures of a) umbeliferone and b) 4-methylumbeliferone coumarin
compounds.
Even though the corresponding PBz materials exhibited high glass transition temperatures (Tg
around 185 °C), the processing of these materials is impeded by high melting temperatures, above
140 °C. However, coumarin-based PBz materials were shown to have relatively high degradation
temperatures, above 300 °C. Consequently, coumarin compounds are considered as competitive
bio-based reagents for the synthesis of high performance PBz materials, comparable to
traditional petroleum-based ones.
110
Bz monomer Tm
(°C)
Tp
(°C)
Tg
(°C)
T5%
(°C) Ref.
1)
Umbeliferone/aniline
147 220 183 327 189
2)
4-methylumbeliferone/aniline
153 232 189 312 190
3)
4-methylumbeliferone/p-toluidine
163 229 - 304 191
Table III - 10. Thermal properties of coumarin-based Bz monomers, synthetized from mono-
functional amines or diamines, and Tg and T5% of their corresponding PBz materials.
1.4.6 Cardanol
Growing interest has arisen towards the synthesis of Bz monomers stemming from Cardanol.
Indeed, the particular chemical structure of cardanol appears as a clear asset for the synthesis of
PBz materials. Cardanol displays a similar reactivity as phenol through the presence of the
hydroxyl group. Furthermore, the long alkyl chain in meta position imparts hydrophobicity and
flexibility, through internal plasticization of the alkyl chain, to the usually brittle PBz materials.
Moreover, the ortho and para positions of cardanol are available for the synthesis of Bz monomers
and their polymerisation respectively.
The chemical structures, as well as the thermal properties of cardanol-based Bz monomers and
their corresponding materials are resumed in Table III - 11.
111
BZ monomer Tm
(°C)
Tp
(°C)
Tg
(°C)
T 5%
(°C) Ref.
1)
Di-cardanol /Ammonia
- 243 36 - 155
2)
Cardanol/Aniline
- 263
58
355
192
3)
4)Cardanol/Stearylamine
- 276
52.8
- 193
4)
Cardanol/Benzylamine
- 263
54
- 193
5)
Cardanol/Furfurylamine
- 271 100 - 194
6)
Cardanol/4,4’-diamino diphenyl sulfone (dds)
- 251 - 299 195
196
7)
Cardanol/ (4-(4-aminophenoxy)phenyl)ether
(44appe)
114 233 - 348 195
196
8)
70 267 - 354 195
196
112
Cardanol/bis-(3-(4-aminophenoxy)phenyl)ether (34
appe)
9)
Cardanol/2,2-bis(4-(4-
aminophenoxy)phenyl)propane (appp)
- 263 - 323 195
196
Table III - 11. Thermal properties of cardanol-based Bz monomers, synthetized from mono-
functional amines or diamines, and Tg and T5% of their corresponding PBz materials.
Almost all of the reported cardanol-based Bz monomers synthesized with short amines did not
display a melting endotherm in response to DSC analysis, as the monomers were in a waxy
amorphous state at ambient temperature. This phenomenon could be attributed to the steric
hindrance generated by the C15 alkyl side chain of cardanol that prevent crystallization.
However, it can be noticed that high melting temperatures were observed for cardanol-based di-
Bz monomers with rigid aromatic diamine as bridging groups, such as bis-(3-(4-
aminophenoxy)phenyl)ether or (4-(4-aminophenoxy)phenyl)ether (Tm = 70 °C and 114 °C
respectively). (Table III – 11, lines 8 and 7)
Generally Bz ring opening polymerization temperatures are ranging from 160 °C to 220 °C,126
while with cardanol, the polymerization temperature were reported to be higher (between 230
°C and 260 °C). The higher polymerization temperatures were certainly due to the steric
hindrance brought by the side chain, impeding the polymerization upon curing. Hence, the
molding and shaping of cardanol-based Bz monomers is facilitated by a wide processing window,
but their overall processing is strongly hampered by high polymerization temperatures (< 230
°C).
Furthermore, it is noteworthy that the thermo-mechanical properties of these PBz materials were
almost never characterized by DMA analysis, as it is very difficult to obtain self-supported
materials due to the steric hindrance of alkyl side chain, yielding to low molecular weight
polymer. Thus, the glass transition temperatures of short amine based PBz reported in the
literature were obtained from DSC analysis (Table III – 11, lines 6 to 9). They are found to be
very low, from 36 °C to 60 °C.
Ambrozic and al. proposed to increase the functionality of the Bz monomer through the reaction
between cardanol and furfurylamine (Table III – 11, line 5).194 The furanic ring of furfurylamine
is highly reactive and promotes thus an increase of the crosslinking density.197 Indeed, when
comparing cardanol-based mono-functional Bz monomers to other amine derivatives, such as
aniline or benzylamine (Tg = 58 °C and 52.8 °C respectively) (Table III – 11, line 2 and 4,
113
respectively) for example, a distinct shift of the Tg to higher temperatures (Tg = 100 °C), was
observed for the furfurylamine-based PBz material. Very interestingly, the use of furfurylamine
accessed to the formation of a self-supported material, which could be analysed by DMA.
Consequently, cardanol-based Bz monomers displayed wide processing windows owing to their
low melting temperatures due to the steric hindrance brought by the C15 alkyl chain. However,
the low crosslinking density and Tg of the corresponding PBz materials, as well as the high
polymerization temperatures, are major drawbacks for the elaboration of high performance
thermosets from cardanol with good thermo-mechanical properties.
1.4.7 Urushiol
Urushiol is another naturally occurring phenolic compound, extracted from lacquer trees. Its
chemical structure is very close to those of cardanol as it is a 3-substituted catechol derivative
with a C15 alkyl chain in meta position. Like for the cardanol compound, the unsaturation degrees
of the alkyl chain, from unsaturated to tri-saturated, and their abundances are varying (Figure
III - 19).
Figure III - 19. Chemical structure of urushiol.
One benzoxazine moiety can be synthetized on the available hydroxyl ortho position of urushiol.
Unlike cardanol, urushiol does not present a free ortho position for the polymerization.
Nevertheless, free para and meta positions are available for the urushiol-based Bz monomers
polymerization (Figure III - 20).
114
Figure III - 20. Available positions for ring opening polymerization of urushiol-based Bz
monomer.
The properties of the Bz monomers synthetized from urushiol are resumed in Table III - 12.
BZ monomer Tm
(°C)
Tp
(°C)
Tg
(°C)
T5%
(°C) Ref.
1)
Urushiol/Aniline
/ 211 140 325 198
2)
Urushiol/N,N diaminodiphenylmethane (ddm)
110 212 135 350 199
Table III - 12. Thermal properties of urushiol-based Bz monomers, synthetized from amines or
diamines, and Tg and T5% of their corresponding PBz materials.
A liquid Bz monomer (Tm < Tamb) was obtained through reaction with paraformaldehyde and
aniline with a polymerization temperature of Tp = 211 °C (Table III – 12, line 1).198 Similarly to
cardanol, urushiol appears as a good precursor for the synthesis of low melting temperature Bz
monomers. In spite of the presence of the long alkyl chain, the corresponding urushiol-based PBz
materials exhibited high glass transition temperatures of 135 °C (urushiol/aniline) and 140 °C
(urushiol/ddm) (Table III – 12, line 1 and 2, respectively) while cardanol/aniline PBz exhibited
a Tg of 58 °C (Chapter III - 1.4.6). Urushiol-based Bz monomers are thus promising for the
development of tough bio-based PBz materials with good thermo-mechanical properties.
In conclusion, the use of naturally occurring phenolic compounds for the synthesis of Bz
monomers allows the lowering of the carbon footprint, and enables the introduction of some
115
additional and/or functional groups within the Bz monomers. Alike petroleum-based Bz
monomers, the nature of the diamine bridging group strongly affects the bio-based Bz monomers
properties and their polymers. Short aliphatic diamine bridging groups, such as ethylene diamine,
should as well be preferred for the synthesis of bio-based Bz monomers. Indeed, the use of short
aliphatic diamines promotes expected moderate processing windows, while resulting in high
crosslinked PBz materials with good thermal and mechanical properties.
Nevertheless, most of the Bz monomers synthetized from bio-based phenolic compounds are
suffering from several disadvantages, either for the synthesis of the Bz monomer, or for the
elaboration and/or for the properties of the final materials. Natural occurring phenolic
compounds such as lignin-derivatives or coumarin compounds lead to highly crosslinked PBz
materials with good thermo-mechanical properties, whereas their processing is hindered by
narrow processing windows. On the contrary, bio-based Bz monomers synthetized from phenolic
compounds like cardanol, urushiol, or eugenol display large processing windows, but low
crosslinking density and low Tg. As the overall performance of PBz is strongly affected by oxazine
ring substitutions, drawbacks of some bio-based phenolic compounds could be offset by the
assets of others to yield Bz monomers with large processing windows and corresponding high
performance PBz materials.
1.5 Asymmetric benzoxazine monomers
1.5.1 State of the art
Bz monomer substitutions can modify their melting temperatures and impact the crosslink
density of the resulting PBz, allowing thus the control of their properties. Additional
functionalities could also be imparted to the monomer by appropriate chemical derivatization of
the Bz monomers as Ishida reported for a new benzoxazine-based surfactants.200 Nevertheless,
due to the symmetric nature of the monomer, the functionalities that could be added are limited
by the chosen phenolic derivative.
An elegant approach of adding different functionalities on Bz monomers consists of designing
asymmetric di-Bz monomers, using for example a diamine as bridging group between two
phenolic derivatives exhibiting each a particular functionality. Different synthesis strategies were
developed in order to access asymmetric di-Bz monomers.
The first example dealing with the synthesis of an asymmetric di-Bz monomer was reported
recently (2013).201 Aminophenol was reacted with the aldehyde group of a hydrobenzaldehyde
compound to form an imine linkage between the two phenolic compounds (Figure III - 21). The
imine was reduced by using NaBH4 and the oxazine rings were further formed using
116
formaldehyde. The second oxazine ring was obtained by ring-closure reaction using a mono-
amine, either butylamine (u-butyl-Bz) or hexylamine (u-hexyl-Bz). Both asymmetric Bz, u-hexyl-
Bz and u-butyl-Bz, have shown similar processing properties (Tp in the range of 210 °C - 240 °C)
with very large processing windows as no melting endotherm was observed on the DSC
thermograms.
Figure III - 21. Synthesis di-Bz asymmetric monomer by reaction between aminophenol and
hydrobenzaldehyde and butylamine (u-butyl-Bz) or hexylamine (u-hexyl-Bz).201
Another possibility is to start from a mixture of symmetric and asymmetric Bz monomers. They
were prepared from phenol, eugenol and 1,4-phenylenediamine by Dubois et al.202 (Figure III -
22). The three Bz monomers were synthetized ‘in-situ’ without a real control of the occurring
reactions. The introduction of an eugenol part within the molecule allowed a solvent-free
synthesis while the phenol part was used to enhance the crosslink density of the resulting
material. The Tg increased from 120 °C to 220 °C with the (phenol : eugenol) ratio ranging from
(1 : 1) to (1.8 : 0.2).
117
Figure III - 22. Synthesis of blends of di-eugenol, di-cardanol and asymmetric eugenol/cardanol
di Bz monomers. 202
Motivated by these approaches, we proposed to design an asymmetric bio-based di-Bz monomer
based on vanillin and cardanol.203 Indeed, symmetric di-Bz monomer synthetized from vanillin
and ethylenediamine (EDA) suffers from a major drawback: its melting temperature (Tm = 218
°C) is too close to its polymerization temperature (Tp = 225 °C) making its processing (molding
and shaping) very challenging.181 To tackle this issue, we aimed in the present work to prepare
bio-phenol based di-Bzs exhibiting large difference between Tm and Tp which can be achievable
by the design of asymmetric di-Bzs with vanillin moiety and another phenolic compound yielding
Bz with low melting temperatures. From previous studies,196 it was expected that cardanol could
be a good candidate to design asymmetric Bz monomers with vanillin to obtain low melting
temperature Bzs and thus expand the processing window. Indeed, the cardanol alkyl side chain
provides better processability and flexibility to the material through internal plasticization.
Furthermore, the presence of the alkyl chain causes steric hindrance, lowering thus the
compound reactivity. Indeed, it was observed that the synthesis of di-vanillin Bz monomer was
straightforward and fast whilst the synthesis of di-cardanol was rather slow. The steric hindrance
brought by the cardanol side chain impeded also its polymerization upon curing, as indicated by
the low enthalpy recorded in DSC for the di-cardanol Bz monomer (32.5 J/g versus 121 J/g for di-
vanillin) as well as the formation of a loosely crosslinked network. Indeed, the steric hindrance
brought by the alkyl chain lead to material with low molecular weight, as attested by the difficulty
to obtain material from di-cardanol Bz that does not creep above Tg.
2 Results and discussion
The detailed experimental conditions are reported in annex p 181.
118
2.1 Symmetric benzoxazine monomers synthesis and characterization
2.1.1 Symmetric Bz monomer synthesis
In a first time, symmetric benzoxazine monomers from phenol, vanillin or cardanol (coined
hereafter di-phenol, di-vanillin and di-cardanol) were synthetized by reacting together phenol or
vanillin or cardanol, paraformaldehyde and ethylene diamine (EDA) is stoichiometric ratio 2:4:1
(Figure III - 23).
Figure III - 23. Synthesis of symmetric Bz monomers from various phenolic compounds like
phenol, vanillin or cardanol.
The structural features of the obtained products were characterized by 1H NMR and HRMS.
2.1.2 Characterization by 1H NMR
- Di-phenol benzoxazine monomer
The 1H NMR spectrum corresponding to the di-phenol Bz monomer is depicted in Figure III - 24.
119
Figure III - 24. 1H NMR spectrum (in CDCl3) of di-phenol benzoxazine monomer.
The 1H NMR spectrum of the reference di-phenol Bz monomer displays the characteristic peaks
of a benzoxazine structure. Indeed, the formation of the Bz was revealed by the presence of peaks
corresponding to the protons from the O-CH2-N and Ar-CH2-N groups. These characteristic groups
were observed in the case of the di-phenol monomer at δ = 4.07 ppm and δ = 4.92 ppm
respectively. Furthermore, the signal integrations were confirming the structure of the di-
benzoxazine from phenol and EDA. The signal of the aromatic protons [1,2,3,4] at δ = 7.15 – 6.78
ppm was taken as integration reference and should integrate for 8 H. Thus, the integrations for
the peaks corresponding to O-CH2-N [6] and Ar-CH2-N [5] were found to integrate for Iexp = 3.73
H and Iexp = 4.02 H respectively as expected (Ith = 4.00 H for each peak). The signal corresponding
to EDA [7] was also observed at δ = 3.02 ppm and Iexp = 4.08 H (Ith = 4.00 H). The 1H NMR analysis
confirmed the expected chemical structure of the di-phenol Bz monomer. The chemical shifts, as
well as their experimental and theoretical integrations are summarized in Table III - 13.
120
Chemical shift
(ppm) Assignment Iexperimental Itheoretical
3.02 N-CH2*-CH2
[7] 4.08 H 4.00 H
4.07 Ar-CH2-N
[5] 4.02 H 4.00 H
4.92 O-CH2-N
[6] 3.73 H 4.00H
7.15 – 6.78 H-Ar
[1,2,3,4] Ref 8.00 H 8.00 H
Table III - 13. Assignments of the 1H NMR peaks of the di-phenol benzoxazine monomer and
their theoretical and experimental integrations.
- Di-vanillin benzoxazine monomer
The 1H NMR spectrum corresponding to the di-vanillin monomer is depicted in Figure III - 25.
Figure III - 25. 1H NMR spectrum (in CDCl3) of di-vanillin benzoxazine monomer.
For the di-vanillin Bz monomer, the peak corresponding to the –OCH3 [6] function of vanillin was
chosen as integration reference. In the case of a di-vanillin monomer, this peak should integrate
for 6H. On the di-vanillin 1H NMR spectrum displayed in Figure III - 25, the characteristic peaks
corresponding to the vanillin compound were revealed. The hydrogens from the aldehyde
121
function [7] appeared at δ = 9.81 ppm with Iexp = 2 H (Ith = 2 H). The integration of aromatic proton
of vanillin [1, 2] at δ = 7.13-7.32 ppm further confirmed the presence of two vanillin moieties (Iexp
= 1.99 H and Ith = 2.00 H). Peaks corresponding to EDA [5] were also observed at δ = 3.02 ppm
where Iexp = 3.70 H (Ith = 4 H). Furthermore, characteristic peaks at δ = 4.13 ppm and at δ = 5.08
ppm, which correspond to the Ar-CH2-N [3] and to O-CH2-N [4] protons respectively, indicated
the formation of di-Bz monomer from vanillin. All the expected theoretical integrations as well as
the corresponding experimental integrations for the di-vanillin monomer are reported in Table
III - 14.
Chemical shift
(ppm) Assignment Iexperimental Itheoretical
3.02 N-CH2*-CH2
[5] 3.70 H 4.00 H
3.95 O-CH3
[6] Ref 6.00 H 6.00 H
4.13 Ar-CH2-N
[3] 4.01 H 4.00 H
5.08 O-CH2-N
[4] 4.02 H 4.00H
7.13 H-Ar
[1, 2] 1.99 H 2.00 H
7.32 H-Ar
[1, 2] 1.99 H 2.00 H
9.81 (C=O)H2
[7] 2.00 H 2.00 H
Table III - 14. Assignments of the 1H NMR peaks of the di-vanillin benzoxazine monomer and
their theoretical and experimental integrations.
- Di-cardanol benzoxazine monomer
Similarly, the structure of the di-cardanol Bz monomer was confirmed by the 1H NMR
characterization (Figure III - 26).
In regard to the integration of the NMR signals relative to the cardanol compound, the precise
integration depends obviously on the composition of cardanol and related proportion of different
isomers. The integrations are usually calculated by moderation based on the abundance of
122
unsaturation described in the literature.11, 51, 204-206 These unsaturation abundances can slightly
vary regarding the origin and the processing of raw Cardanol extracted from CNSL. As such the
integration may diverge from sample to other. The unsaturations abundances of the used
cardanol were considered as following: tri-unsaturated (n=3) ~ 41%, di-unsaturated (n=2) ~
23%, mono-saturated (n=1) ~ 34%, saturated (n=0) ~ 3%.11, 50, 204-206 In addition, the difference
of relaxation times between aromatic and aliphatic hydrogen may complicate the accurate
quantification of all protons. Therefore, the peaks related to the aliphatic chain of cardanol were
integrated to the aliphatic hydrogen in β position of the cardanol aromatic ring, which should
integrate for 2H.
Figure III - 26. 1H NMR spectrum (in CDCl3) of di-cardanol benzoxazine monomer.
The characteristic peaks of cardanol were observed, especially the aromatic protons [1, 2, 3] at δ
= 6.60 – 6.88 ppm which integrate each for about 2 H (see Table III - 15) indicating the probable
presence of two cardanol moieties within the monomer. This was further confirmed by the
integration of the following peaks from cardanol , the alkyl chain olefinic CH2 protons [b2, d2, e2,
g2, h2, a2] at δ = 4.96 – 5.88 ppm, the protons in α of the alkyl chain unsaturations [c2, f2, i2] at δ =
1.98 – 2.09 ppm, as well as the CH2 protons in α of the aromatic [o] at δ = 2.49 – 2.57 ppm, the CH2
from the alkyl chain [b1, c1, d1, e1, f1, g1, h1, i1, j, k, l, m, n] at δ = 1.23 – 1.43 ppm and the CH3 of the
alkyl chain [a1] at δ = 0.86 – 0.94 ppm. The CH2 of the alkyl chain comprised between two
unsaturations [c3, f3] were detected at δ = 2.76-2.87 ppm. The experimental and theoretical
integrations of the di-cardanol Bz compound peaks are reported in the Table III - 15. As it can be
observed, the experimental integrations of the peaks corresponding to the cardanol moiety are
123
close to the expected integrations for the di-cardanol Bz monomer containing two cardanol
moieties.
The formation of the benzoxazine structure was verified by the presence of benzoxazine
characteristic peaks at δ = 4.03 ppm and at δ = 4.89 ppm corresponding to Ar-CH2-N [4] and to O-
CH2-N [5] respectively, both peaks integrating as expected for approximately 4.00 H.
Chemical shift
(ppm) Assignment Iexperimental Itheoretical
0.86 – 0.94 -CH3
[a1] 4.08 H 3.54 H
1.23 – 1.43
-CH2
[b1, c1, d1, e1, f1, g1,
h1, i1, j, k, l, m, n]
27.58 H 27.12 H
1.54 – 1.64 -CH2 in β from Ar
[n] 4.00 H 4.00 H
1.98 – 2.09 CH2*=CH
[c2, f2, i2] 7.47 H 6.20 H
2.49 – 2.57 CH2-Ar
[o] 4.47 H 4.00 H
2.76 – 2.87 CH2*(=CH)2
[c3, f3] 4.74 H 4.20 H
2.99 N-CH2*-CH2
[6, 7] Ref 4.00 H 4.00 H
4.03 Ar-CH2-N
[4] 3.98 H 4.00 H
4.89 O-CH2-N
[5] 4.00 H 4.00 H
4.96 – 5.88 CH=
[b2, d2, e2, g2, h2, a2] 1.69; 7.55; 0.94 H 1.64; 6.48; 0.82 H
6.60 – 6.90 H-Ar
[1, 2, 3] 2.01; 2.07; 1.93 H 2.00; 2.00; 2.00 H
Table III - 15. Assignments of the 1H NMR peaks of the di-cardanol benzoxazine monomer and
their theoretical and experimental integrations.
124
*Matrix
2.1.3 Characterization by MALDI-TOF/MS or HRMS
The chemical structure of the di-phenol symmetric Bz monomer were confirmed by MALDI-
TOF/MS characterisation, and by High Resolution Mass Spectrometry (HRMS) characterisation
for the di-vanillin and di-cardanol monomers.
- Di-phenol benzoxazine monomer
The chemical structure of the synthetized reference di-phenol Bz monomer was characterized by
MALDI-TOF/MS. The corresponding spectrum is displayed in Figure III - 27.
Figure III - 27. MALDI-TOF/MS spectrum of di-phenol benzoxazine monomer.
The expected protonated compound [M+H]+ was observed at m/z 297. Nevertheless, ions at m/z
285 and at m/z 283, assigned as [M+H+H2O-CH2O]+ and [M-H+H2O-CH2O]+ resulting from a
reaction during the analysis timeframe were also detected, as expected from mass spectrometry
analyses of Bz monomers. 207, 208 Indeed, di-Bz monomers were found to strongly react during the
timeframe of mass analysis through ion/molecules reactions upon the addition of water and the
subsequent release of formaldehyde from the protonated compound. Since air humidity
encountered during the preparation undoubtedly accounts for this ion/molecule reaction, their
occurrences have not been avoided despite the use of a solvent-free sample preparation.
125
- Di-vanillin benzoxazine monomer
The HRMS spectrum of the di-vanillin Bz monomer is displayed in Figure III - 28.
Figure III - 28. HRMS spectrum of di-vanillin benzoxazine monomer.
The protonated specie of di-vanillin [M+H]+ appeared at m/z 413, confirming the formation of a
di-Bz monomer from vanillin. Likewise for the di-phenol Bz monomer, ions at m/z 401 and at m/z
399, assigned as [M+H+H2O-CH2O]+ and [M-H+H2O-CH2O]+ resulting from a reaction during the
analysis timeframe were also detected as expected.
A zoom of this spectrum region is visible on the Figure III - 29 as well as the theoretical mass
spectrum expected for the di-vanillin compound.
Figure III - 29. HRMS analysis of di-vanillin Bz monomer a) Zoom of the experimental product
peaks b) Theoretical mass of the expected product.
126
As observed in the Figure III - 29, the di-vanillin Bz monomer was detected at m/z 413.1703. The
mass of the di-vanillin Bz monomer is very close to the expected mass of m/z 413.1707,
confirming the chemical structure verified by the previous 1H NMR analysis.
- Di-cardanol benzoxazine monomer
Likewise for the di-vanillin monomer, the expected typical peaks of di-cardanol Bz were present
in the corresponding HRMS spectrum: the compound protonated specie [M+H]+ appeared at m/z
709 as well as at m/z 696 and at m/z 694, assigned as [M+H+H2O-CH2O]+ and [M-H+H2O-CH2O]+
ions of di-cardanol Bz monomer respectively (Figure III - 30).
Figure III - 30. HRMS spectrum of di-cardanol benzoxazine monomer.
A zoom of this spectrum region as well as the theoretical mass spectrum expected for the di-
cardanol Bz monomer is displayed in Figure III - 31.
Figure III - 31. HRMS analysis of di-cardanol Bz monomer a) Zoom of the experimental product
peaks b) Theoretical mass of the expected product.
127
The experimental mass observed for di-cardanol at m/z 709.5668 is very close to the expected
theoretical mass of m/z 709.5667, confirming the chemical structure of di-cardanol Bz
compound.
Nevertheless, some unexpected additional peaks were observed around m/z 380-400 (Figure III
- 30). In order to verify that these peaks are not impurities but fragments of the original di-
cardanol compound, MS/MS analysis was achieved on the monomer.
As it can be readily observed on the MS/MS spectrum of the di-cardanol Bz monomer (Figure III
- 32), remaining peaks at m/z 401, 383, and 358 were resulting from fragmentation during the
analysis timeframe.
Figure III - 32. MS/MS analysis of di-cardanol Bz monomer.
In conclusion, the synthetized compounds appear to be pure as confirmed by the MALDI/TOF-
MD and HRMS characterizations.
2.1.4 Characterization by DSC and TGA
The thermal behaviour of the symmetric monomers was investigated by DSC and TGA analyses.
For each monomer, the DSC and TGA analyses were carried out at a heating rate of 20 K/min
under nitrogen atmosphere.
- Di-phenol Bz monomer
The DSC and TGA analysis of the di-phenol monomer are displayed in Figure III - 33. The DSC
analysis revealed a moderate processing window of the di-phenol monomer with Tm = 115 °C and
128
Tp = 212 °C. The processing of this monomer to a polybenzoxazine material is thus relatively easy.
Furthermore, it can be observed on the TGA analysis that the monomer was able to polymerize
at elevate temperatures, around 210 °C, before undergoing thermal degradation (T5% = 287 °C).
Figure III - 33. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of di-phenol monomer.
- Di-vanillin Bz monomer
As it can be observed on the Figure III - 34, the di-vanillin Bz monomer displayed a relatively
high melting temperature of Tm = 218 °C, barely distinguished from the maximum exothermic
peak temperature of ring-opening reaction occurring at Tp = 225 °C. These close transition
temperatures, impede the monomer processing (molding and shaping), as the monomers
polymerization begins quasi simultaneously with its melting. The high melting temperature of di-
vanillin Bz monomer is probably inducted by the presence of the formyl group on vanillin,
promoting the formation of a stiff crystalline structure brought by intra- and inter-molecular H
bonding network.
In addition, the TGA analysis (Figure III - 34) revealed an early thermal degradation of the
monomer, even before the melting (T5% = 203 °C), further impeding the elaboration of a
polybenzoxazine material from the di-vanillin monomer.
129
Figure III - 34. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of di-vanillin Bz monomer.
- Di-cardanol Bz monomer
In contrary to the di-vanillin compound, the di-cardanol Bz monomer exhibited a low melting
temperature of Tm = 44 °C. This result is most probably due to the presence of the C15 alkyl side
chain in meta position. Indeed, cardanol is well-known to provide flexibility to materials through
plasticizing effect. The polymerization temperature was found to be at Tp = 219 °C, within the
expected polymerization temperature range of di-Bz monomers. The di-cardanol Bz monomer
presents thus the advantage of a very large processing window.
Furthermore, when comparing the DSC and TGA analysis (Figure III - 35), it can be observed that
the di-cardanol Bz monomer thermal degradation occured at higher temperature than its ring
opening polymerization temperature. Indeed, T5% = 260 °C whereas Tp = 219 °C, indicating that
the monomer is able to polymerize without early thermal degradation. Moreover, it can be noted
that the thermal degradation temperature for the di-cardanol Bz monomer was much higher than
the degradation temperature of the di-vanillin Bz monomer (T5% = 203 °C).
130
Figure III - 35. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of the di-cardanol
benzoxazine monomer.
2.1.5 Characterization by rheology analysis
Rheology experiments were monitored for each symmetric Bz monomer in order to evaluate their
polymerization reactivity. The polymerization measurements were achieved with a plate-plate
geometry (diameter 25 mm, measure gap 0.5 mm) and recorded at an imposed 1 % deformation
at 1 Hz frequency at 190 °C.
It is worth indicating the unsuccessful monitoring of rheology experiments for di-vanillin Bz due
to the (quasi) simultaneous monomers melting, polymerization and thermal degradation. Indeed,
di-vanillin Bz exhibits a relatively high melting temperature (Tm = 218 °C) barely distinguished
from the maximum exothermic peak temperature of ring-opening reaction occurring at Tp = 225
°C (Figure III - 34). These close transition temperatures, in addition to the early thermal
degradation of the monomer (203 °C), impede its elaboration. Efforts to moderate the reactivity
by adjusting the curing conditions were unsuccessful.
- di-phenol Bz monomer
The rheo-kinetic characterization of the di-phenol Bz monomer upon polymerization is displayed
in Figure III - 36. The di-phenol Bz monomer crosslinking at 190 °C was evidenced by the rapid
increase of the storage and the loss modulus. The recorded gelation time, corresponding to the
crossover point of G’ and G’’, was very short as it is found to be in the range of [4-5] min,
confirming thus the high reactivity of di-phenol Bz monomer.
131
Figure III - 36. Isothermal rheology monitoring of di-phenol Bz monomer at 190 °C – empty
markers: storage modulus G’; filled markers: loss modulus G’’.
- di-cardanol Bz monomer
The rheogram, depicted in Figure III - 37, represents the evolution of the storage modulus G’ and
the loss modulus G’’ of the di- cardanol Bz monomer during their polymerization at 190 °C. Full
ploted rheogram is depicted in Annex Figure 2 p 190.
Figure III - 37. Isothermal rheology monitoring of di-cardanol Bz monomer at 190 °C – empty
markers: storage modulus G’; filled markers: loss modulus G’’.
132
The behaviour of di-cardanol upon heating is typical to thermosets with a significant increase of
both G’ and G’’, evidencing the starting of the crosslinking at 190 °C. The gelation time, was
observed in the range of [30-31] min highlighting the low reactivity of di-cardanol Bz monomers.
In conclusion, cardanol di-Bz monomer was found to display a large processing window (ΔTproc =
175 °C) due to very low melting temperature (Tm = 44 °C), which makes it an interesting precursor
for easily processable bio-based Bz. Indeed, when comparing to the di-phenol Bz monomer (Tm =
115, ΔTproc = 97 °C), the presence of the cardanol alkyl chain seemed to favorise lower melting
temperatures, probably due to sterical hindrance. However, the steric hindrance brought by this
side chain seemed to impede its polymerization upon curing as indicated by its very long gelation
time [30-31] min at 190 °C recorded in rheology experiments (di-phenol Bz monomer Tgel = [4-
5] min at 190 °C) and low enthalpy recorded in DSC (22.6 kJ/mol versus 49.9 kJ/mol for di-vanillin
Bz for example).
In consequence, the di-cardanol Bz monomer is interesting because of its low melting
temperature but the corresponding PBz material elaboration is nevertheless impeded by a long
gelation time and steric hindrance resulting in a poorly crosslinked polymer material. The use of
the di-vanillin Bz monomer to synthesize a self-standing PBz material on the contrary is hindered
by a too high melting temperature overlapping its polymerization and thermal degradation.
However, the good thermal properties of di-vanillin PBz due to the aldehyde function of vanillin
Bz are very encouraging.
Thus, we propose an innovative strategy to lower vanillin-based Bz monomers melting
temperatures in order to enable their processing. Cardanol was shown to provide, through
plasticizing effect of the C15 alkyl chain, flexibility to the resulting materials and to result in Bz
monomer with low melting temperature. More importantly, the low reactivity of cardanol driven
by its structural features offers therefore the possibility to control the synthesis of a mono-
cardanol Bz with a free primary amine moiety that can be further coupled with another bio-based
phenol like vanillin. We propose in the following part a synthesis of asymmetric monomers
combining cardanol and vanillin displaying low melting temperature and accessing PBz materials
with good thermo-mechanical properties.
2.2 Asymmetric benzoxazine monomers synthesis and characterization
2.2.1 Asymmetric Bz monomer synthesis
Accordingly, with an appropriate adjustment of the reagents stoichiometry, asymmetric
benzoxazine monomers were synthetized (cardanol, EDA, paraformaldehyde reacted in CHCl3 at
70 °C under reflux in stoichiometric ratio 1:1:2), mono-substituted cardanol-benzoxazine was
133
obtained. To produce the so-called Vani-Card asymmetric Bz monomer, vanillin was added in a
second step to the precedent reaction crude with paraformaldehyde in stoichiometric ratio 1:2
and reacted at 70 °C (Figure III - 38).
Figure III - 38. Synthesis of the asymmetric Vani-Card Bz monomer from cardanol and vanillin.
High yield (72 %) of Vani-Card Bz monomer was obtained as confirmed by 1H NMR and HRMS
(Figure III - 39 and - 40 respectively).
2.2.2 Characterization by 1H NMR
The recorded 1H NMR spectrum of Vani-Card is displayed in Figure III - 39. The spectrum
revealed the presence of characteristic peaks corresponding to the formation of the asymmetric
Bz monomer.
As previously mentioned, the precise integration of the NMR signals corresponding to peaks
relative to the cardanol compound, depends on the composition of cardanol and related
proportion of different isomers. The integrations are usually calculated by moderation based on
the abundance of unsaturation described in the literature. In addition to varying unsaturation
abundances, the difference of relaxing times between aromatic and aliphatic hydrogen may
complicate the precise quantification of all hydrogen from this asymmetric monomer.
An accurate integration was optimized where the –OCH3 function from the vanillin compound
was taken as integration reference for the peaks corresponding to the benzoxazine structure. This
peak should integrate for 3 H. As the cardanol alkyl chain unsaturation degree is varying and the
134
relaxation times are differing from the other hydrogens, the related peaks will be integrated on
another reference. The aliphatic hydrogen in β position of the cardanol aromatic ring was taken
as integration reference and should integrate for 2 H.
Figure III - 39. 1H NMR spectrum (in CDCl3) of Vani-Card benzoxazine monomer.
First of all, the characteristic peaks of cardanol were observed, such as the aromatic protons [1,
2, 3] at δ = 6.60 – 6.88 ppm which integrate each for about 1 H (see Table III - 16) indicating
probably the presence of only one cardanol moiety within the monomer. This was further
corroborated by the integration of the remaining peaks from cardanol, the alkyl chain olefinic CH2
protons [b2, d2, e2, g2, h2, a2] at δ = 4.96 – 5.88 ppm, the protons in α of the alkyl chain
unsaturations [c2, f2, i2] at δ = 1.98 – 2.09 ppm, as well as the CH2 protons in α of the aromatic [o]
at δ = 2.49 – 2.57 ppm, the CH2 from the alkyl chain [b1, c1, d1, e1, f1, g1, h1, i1, j, k, l, m, n] at δ = 1.23
– 1.43 ppm and the CH3 of the alkyl chain [a1] at δ = 0.86 – 0.94 ppm. The CH2 of the alkyl chain
comprised between two unsaturations [c3, f3] were detected at δ = 2.76-2.87 ppm. The
experimental and theoretical integrations of the peaks corresponding to the cardanol moiety of
the Vani-Card monomer are reported in the Table III - 16 with the aliphatic hydrogen in β
position of the cardanol aromatic ring, as integration reference (I = 2 H). As it can be observed,
the experimental integrations of the peaks corresponding to the cardanol moiety are close to the
expected integrations for Vani-Card Bz monomer containing one cardanol moiety.
For the vanillin moiety of Vani-Card Bz monomer, the peak corresponding to the –OCH3 function
of vanillin [13] at δ = 3.86 – 3.94 ppm was chosen as integration reference. This peak should
135
integrate for 3H (I = 3 H). The characteristic peaks corresponding to the vanillin compound
moiety were revealed in the NMR spectrum. The hydrogens from the aldehyde function [11]
appeared at δ = 9.81 ppm with Iexp = 1.01 H (Ith = 1.00 H). The integration of aromatic proton of
vanillin [10, 12] at δ = 7.12 - 7.34 ppm further confirmed the presence of one vanillin moiety (Iexp
= 1.00 and 1.01 H and Ith = 1.00 and 1.00 H). Peaks corresponding to EDA [6, 7] were also observed
at δ = 2.95 – 3.09 ppm where Iexp = 3.99 H (Ith = 4.00 H).
Furthermore, characteristic peaks at δ = 4.01 ppm and δ = 4.13 ppm assigned to Ar-CH2-N of
cardanol- [4] and vanillin-based [9] oxazine moieties respectively were detected, as well as at δ =
4.88 ppm and δ = 5.08 ppm assigned to O-CH2-N of cardanol- [5] and vanillin-based [8] oxazine
moieties respectively, attesting the formation of an asymmetric di-Bz monomer from vanillin and
cardanol.
Chemical shift
(ppm) Assignment
Compound
reference Iexperimental Itheoretical
0.85 – 0.96 -CH3
[a1] cardanol 2.04 H 1.77 H
1.23 – 1.41
-CH2
[b1, c1, d1, e1, f1,
g1, h1, i1, j, k, l, m,
n]
cardanol 13.53 H 13.56 H
1.54 – 1.64 -CH2 in β from Ar
[n] cardanol Ref 2.00 H 2.00 H
1.98 – 2.09 CH2*=CH
[c2, f2, i2] cardanol 3.41 H 3.10 H
2.49 – 2.56 CH2-Ar
[o] cardanol 2.00 H 2.00 H
2.75 – 2.87 CH2*(=CH)2
[c3, f3] cardanol 2.36 H 2.10 H
2.95 – 3.09 N-CH2*-CH2
[6, 7] benzoxazine 3.99 H 4.00 H
3.86 – 3.94 O-CH3
[13] Benzoxazine Ref 3.00 H Ref 3.00 H
4.01 Ar-CH2-N
[4] cardanol 1.99 H 2.00 H
4.13 Ar-CH2-N benzoxazine 1.99 H 2.00 H
136
[9]
4.88 O-CH2-N
[5] cardanol 1.98 H 2.00 H
4.96 – 5.88
CH=
[b2, d2, e2, g2, h2,
a2]
cardanol 1.00; 3.76; 0.46 H 0.82; 3.24; 0.41
H
5.08 O-CH2-N
[8] benzoxazine 1.99 H 2.00 H
6.60 – 6.99 H-Ar
[1, 2, 3] cardanol 1.07; 1.06; 1.00 H
1.00; 1.00; 1.00
H
7.12 – 7.34 H-Ar
[10, 12] benzoxazine 1.00; 1.01 H 1.00; 1.00 H
9.81 (C=O)H
[11] benzoxazine 1.01 H 1.00 H
Table III - 16. Assignments of the 1H NMR peaks of the asymmetric Vani-Card Bz monomer and
their theoretical and experimental integrations.
2.2.3 Characterization by MALDI-TOF/MS
The asymmetric Bz monomer was also successfully detected by mass analysis (Figure III – 40a)
as the protonated Vani-Card specie was observed at m/z 559, as well as the expected ions
[M+H+H2O-CH2O]+ at m/z 547 and [M-H+H2O-CH2O]+ at m/z = 545.
The theoretical expected mass of Vani-Card is displayed on Figure III – 40b. The mass found for
the asymmetric monomer m/z 559.3531 is very close to the theoretical mass expected of m/z
559.3530, confirming the formation of the expected Vani-Card monomer.
137
Figure III - 40. HRMS analysis of Vani-Card Bz monomer a) Zoom of the experimental product
peaks b) Theoretical mass of the expected product.
Nevertheless, some additional peaks could be observed around m/z 400 (Figure III – 41). Those
peaks at m/z 399, 383 and 358 on the Vani-Card spectrum were resulting from the monomer
fragmentation during the mass analysis timeframe of the cardanol-based benzoxazine part of the
Vani-Card monomer. Indeed, as it can be observed on the MS/MS spectrum of the di-cardanol
monomer (Figure III - 32), some peaks resulting from fragmentation were readily detected at
m/z = 399-405, 383-387 and 358.
Figure III - 41. HRMS spectrum of Vani-Card benzoxazine monomer.
138
2.2.4 Characterization by DSC
The thermal behaviour of the asymmetric Vani-Card Bz monomer was investigated by DSC
analysis, and compared to the symmetric di-vanillin and di-cardanol Bz monomers. For each
monomer, the DSC analysis was carried out at a heating rate of 20 K/min under nitrogen
atmosphere.
The DSC analyses of the asymmetric Vani-Card Bz monomer and of the symmetric di-vanillin and
di-cardanol Bz monomers are displayed in Figure III - 42.
Figure III - 42. DSC thermograms (N2, 20 K/min) of a) di-vanillin, b) Vani-Card Bz monomers
and c) di-cardanol Bz monomer.
Alike symmetric Bz monomers, the DSC thermograms of the asymmetric monomer (Figure III -
42b) showed an endothermic peak corresponding to the monomer melting temperature around
101 °C, and an exothermic peak, in the range of 200-250 °C, assigned to the curing by thermal-
activated ring-opening of the Bz monomer. It can be noticed that the melting temperature was
significantly decreased from Tm = 218 °C recorded for di-vanillin Bz to Tm = 101 °C for Vani-Card
enlarging therefore the processing temperature frame. The drastic melting temperature decrease
when substituting one vanillin moiety by cardanol compound is attributed most likely to the C15
alkyl side chain that disturbed the ordered structure of di-vanillin benzoxazines. Interestingly,
139
the temperatures of the ring-opening polymerization were slightly affected and remained in the
range of catalyst-free ring-opening reactions of Bz regardless the nature of the phenol. Indeed, Tp
shifted only from 225 °C to 227 °C for di-vanillin and Vani-Card Bz monomers respectively. These
results were consistent with those reported by Allen et al.209 who evidenced that the phenol
substitution strongly impacts the melting temperatures of Bz monomers, without influencing the
ring-opening polymerization temperature.
Moreover, it is important to notice that contrary to the di-vanillin Bz monomer, the thermal
degradation of Vani-Card Bz monomer occurred at higher temperature (T5% = 280 °C) than its
polymerization temperature (Tp = 227 °C) (Figure III - 43), further confirming the possibility of
elaborating PBz material from the Vani-Card Bz monomer.
Figure III - 43. DSC (N2, 20 k/min) and TGA (N2, 20 k/min) analyses of the Vani-Card Bz
monomer.
2.2.5 Characterization by rheology analysis
Rheology experiment was monitored for the asymmetric Bz monomer in order to evaluate its
polymerization reactivity and to compare it to the reactivity of the symmetric di-cardanol Bz
monomer. The polymerization measurements were achieved with plate-plate geometry
(diameter 25 mm, measure gap 0.5 mm) and recorded at an imposed 1 % deformation at 1 Hz
frequency at 190 °C. Full plot rheogram is depicted in Annex Figure 3 p 191.
From a processing point of view, first and foremost, the synthesized asymmetric Vani-Card Bz
exhibited a moderate gelation time ([8-9] min at 190 °C, Figure III - 44) as opposed to di-cardanol
monomers for which the gelation time was very long at the same temperature, and to the di-
vanillin monomer which polymerization could not be recorded by rheology due to its high melting
temperature and close degradation temperature. Vani-Card gelation time was far below values
140
reported for relevant bis-phenol-A/aniline Bz cured at 190 °C for which is around 39.9 min for
example.210
Figure III - 44. Isothermal rheology monitoring of Vani-Card (circular markers) and di-cardanol
(triangular markers) benzoxazines at 190°C – empty markers: storage modulus G’; filled
markers: loss modulus G’’.
The Vani-Card Bz monomer displays thus an enhanced reactivity, highlighted by a relative low
gelation time in comparison to a di-cardanol Bz monomer.
The properties of the symmetric and asymmetric Bz monomers are summarized in Table III - 17.
Bz monomer Tm a (°C) Tp a (°C) ∆H a (kJ/mol) T5% b (°C) Tgel c (min)
di-Vanillin 218 225 49.9 203 -
di-Cardanol 44 219 22.6 260 [30-31]
Vani-Card 101 227 45.0 280 [8-9]
Di-phenol 115 212 - 287 [4-5]
Table III - 17. Thermal properties of symmetric and asymmetric di-benzoxazine monomers.
Values are obtained from DSC (a), TGA (b) and rheology (c) analyses.
In Table III - 17 are also reported the melting and polymerization temperatures of a model
benzoxazine monomers prepared from the bridging of two phenols with ethylenediamine (so-
called di-phenol). Di-phenol Tm (115 °C) and Tp (212 °C) (Figure III - 33,) are similar to those of
Vani-Card, emphasizing the capability of Vani-Card to be processed as well as a short amine
bridged petroleum-based benzoxazine monomer.
141
In conclusion, the Vani-Card Bz monomer, through interesting properties of such as a low Tm and
thus a moderate processing window, as well as a high thermal degradation temperature and a
relative short gelation time, appears as a promising precursor for the elaboration of bio-based
PBz material with good properties.
2.3 Materials elaboration and characterizations
2.3.1 Materials elaboration
Polybenzoxazine materials were elaborated from the symmetric di-cardanol Bz monomer as well
as from the asymmetric Vani-Card Bz monomer, and their characteristics were compared.
The monomers were degassed during 1 h above melting temperature (50 and 105 °C, for Vani-
Card and di-cardanol Bz respectively) and then transferred to a U-shaped mold. A curing program
of 1 h at 160 °C was applied followed by 2 h at 180 °C and the samples were post-cured for 2 h at
200 °C and 30 min at 220 °C.
2.3.2 DMA characterization
DMA characterizations of polymerized Vani-Card and di-cardanol Bz, so-called poly(Vani-Card)
and poly(di-cardanol), are reported on Figure III - 45. Surprisingly, poly(di-cardanol) started
creeping above 80 °C as attested by the absence of caoutchoutic state in its thermo-mechanical
behaviour and confirmed by the picture of the material at the end of the test, inserted in Figure
III - 45. On the contrary, the asymmetric poly(Vani-Card) presented a thermoset-like behaviour
upon heating and its Tα was reached at 129 °C, according to the maximum of the tan δ peak.
The cardanol side chain had a clear plasticization effect on both materials (symmetrical and
asymmetrical based on cardanol) as compared to the Tα of poly(di-phenol) (160 °C), but resulted
in a thermoplastic material in the case of poly(di-cardanol). The substitution of one unit of
cardanol by vanillin within the monomer allowed a sufficient increase of the Vani-Card PBz
crosslinking density to yield a self-supported thermoset material.
In addition, the vanillin formyl group within the material should increase the material stiffness
most probably through the formation of strong intra- and inter-molecular H-bonding. The storage
modulus in the glassy state also increased from 150 MPa for poly(di-cardanol) to 700 MPa for
poly(Vani-Card). These values of storage modulus seemed to be similar to those described in the
literature. Ishida and Agag reported a storage modulus of 450 MPa in the glassy state for a
polybenzoxazine prepared from CNSL and aromatic 4,4’-diaminophenyl methane.211 In spite of
the aromatic diamine used by the authors, poly(Vani-Card) enabled to reach a material with
higher stiffness due to the presence of the vanillin moiety.
142
Figure III - 45. DMA thermograms of poly(di-cardanol), poly(di-phenol) and poly(Vani-Card).
The DMA analysis of the asymmetric poly(Vani-Card) material revealed the elaboration of a self-
supported PBz material from the Vani-Card Bz monomer displaying good thermal properties in
comparison to a traditional poly(di-phenol) material.
Finally, the new poly(Vani-Card) material was compared in term of thermal stability by
thermogravimetric analyses under air atmosphere to poly(di-cardanol) and poly(di-phenol)
(Figure III – 46).
As poly(di-vanillin) could not be elaborated, we report on Figure III - 46 the evolution of the
percentage of mass loss (wt%) for a poly(di-phenol) for the sake of comparison. The onset
degradation temperature of poly(di-phenol) was quite low (around 230 °C) due to the
fragmentation of the Schiff bases. The presence of cardanol in poly(Vani-Card) and poly(di-
cardanol) seemed to prevent this first degradation step. Yet, the onset of the thermal degradation
for poly(Vani-Card) and poly(di-cardanol) materials were unexpectedly high (T5% = 373 °C and
398 °C respectively) given the presence of unsaturation that are commonly known to promote
the chain scission and therefore the thermal degradation of polymers.
In conclusion, the TGA analysis of the symmetric and asymmetric PBz materials highlighted the
increase of the thermal degradation temperature for PBz materials containing at least one
cardanol moiety (poly(di-cardanol) and poly(Vani-Card)).
143
Figure III - 46. TGA (air atmosphere, 20K/min) thermograms of a) di-cardanol, b) di-phenol
and c) Vani-Card PBz materials.
The thermal and mechanical properties of the symmetric poly(di-cardanol) and poly(di-phenol)
and of the asymmetric poly(Vani-Card) materials are gathered in Table III - 18.
PBz materials Tg (°C)a T5% b (°C) Tmax b (°C)
Poly(di-Cardanol) - 398 456
Poly(Vani-Card) 129 373 440
Poly(Di-phenol) 160 273 407
Table III - 18. Thermal properties of symmetric and asymmetric PBz materials. Values are
obtained from DMA (a), and TGA (b) analyses.
3 Conclusions
In conclusion, the first part of this study highlighted the difficulty to synthetize PBz materials from
bio-based di-Bz monomers. Indeed, elaboration of a PBz material from di-vanillin Bz monomer
for example was strongly hampered by the high melting temperature of the monomer Tm = 218
°C), overlapping the polymerization (Tp = 225 °C). On the contrary, di-cardanol Bz monomers
presented the great advantage of displaying a low melting temperature (Tm = 44 °C), facilitating
the materials processing (ΔTproc = 175 °C). Due to the sterical hindrance of the cardanol alkyl side
chain, the material was poorly crosslinked and started creeping around 80 °C. Finally, this
roundabout was allowing the synthesis of an easy processable thermoplastic material based on
PBz, which is quite rare in the literature.
With the aim to combine the good thermal properties of vanillin-based Bzs (possible H bonding
through the aldehyde function) and the low melting temperature of the cardanol-based Bz
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monomer, we reported an efficient preparation of asymmetric bio-based di-benzoxazines (named
Vani-Card) via a two-step synthesis pathway including a controlled mono-substitution of
cardanol-based benzoxazines followed by a coupling with vanillin. Such combination resulted in
a substantial decrease of the melting temperature (Tm = 101 °C), without any impact on the
activation temperature (Tp = 227 °C) enlarging therefore the processing window of these bio-
based thermosets (ΔTproc = 126 °C, compared to ΔTproc = 7 °C for di-vanillin Bz). Furthermore, a
second drawback of the di-vanillin Bz monomers was their thermal degradation occurring
simultaneously to their melting and even before their polymerization (T5% = 203 °C). In the case
of the asymmetric Vani-Card Bz monomer, no problem of thermal degradation of the monomer is
further encounter due to the presence of the cardanol moiety. Indeed, the thermal degradation of
the Vani-Card monomer occurred at higher temperature than melting and polymerization (T5% =
280 °C).
The asymmetric Bz monomer enabled thus, through a processing point of view, an easy
elaboration of a cardanol- and vanillin-based PBz material. Furthermore, the synthesis of the
asymmetric Vani-Card monomer was also shown to strongly influence the reactivity of the
monomer. Indeed, the di-cardanol Bz monomer displayed a long gelation time (Tgel = [30-31] min
at 190°C) in comparison to a classical di-phenol Bz monomer (Tgel = [4-5] min at 190°C). In the
case of Vani-Card Bz, an interesting moderate gelation time of 8-9 min was reported.
Moreover, the characterizations of the asymmetric PBz material highlighted the obtaining of a
thermoset material with good thermo-mechanical properties. Indeed, a Tg of 129 °C and a storage
modulus in the glassy state of 700 MPa were reported, indicating that Vani-Card PBz material
displayed very comparable thermal and mechanical properties to other known polybenzoxazines
particularly those partially or fully based on renewable compounds.
Finally the presence of the cardanol moiety was shown to strongly influence the thermal stability
of the PBz material. Indeed, a high thermal degradation onset temperature was recorded for Vani-
Card PBz material (T5% = 373 °C) compared to classical di-phenol PBz material (T5% = 273 °C).
This versatile approach is a powerful tool to access a wide range of bio-based asymmetric
benzoxazines given the large number of precursors available and their possible combination. It
paves the way toward easily processable high performance bio-based benzoxazines. This strategy
could for example be applied to further improve the processing of bio-based di-Bz monomers.
Indeed, the high polymerization temperature of Bz monomers remains a major drawback for
their spreading for industrial applications. The use of lignin-derivative phenolic compounds
bearing a carboxylic acid function for the synthesis of mono-Bz monomers were recently reported
by Comi et al.184. The presence of the –COOH function was reported to induce a lowering of the Bz
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ring opening polymerization temperature. However, among others, the main drawback of these
monomers was there to high melting temperature, close to their polymerization temperature,
hindering the processing of the materials. The synthesis of asymmetric monomers between
cardanol and bio-based phenolics bearing carboxylic acid functionalities could be an interesting
method to lower the polymerization temperature of the Bz while facilitating their processing.
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Chapter IV: Interpenetrating Polymer Networks (IPN) from a cardanol-based thermoset network
1 Introduction
Nowadays, the use of conventional petroleum-based epoxy thermosets is being compromised not
only for the foreseen shortage in oil resources, but also because widely used components such as
Bisphenol A (BPA), identified as an endocrine disruptor, wreak havoc on the human health. This
is why researchers are focusing on the development of totally or partially bio-based and potential
environmentally friendly BPA-free epoxy thermosets. Among the most promising bio-based
alternatives, cardanol has attracted a tremendous level of interest within the materials
community. In particular, di-glycidyl ether of cardanol (CDGE) (Figure IV - 1) could be considered
as a viable alternative to traditional thermosets prepared from BADGE.
Figure IV - 1. Chemical structure of diglycidyl ether of cardanol (CDGE) – commercially
available NC514 - from Cardolite Corporation.
However, its low thermal and water resistance properties are important drawbacks to a wider
range of applications. Reinforcement of CDGE-based networks could be performed from a
macromolecular approach by the interpenetration of a polybenzoxazine network. Indeed, as
described earlier in this manuscript, benzoxazines have excellent thermal properties and have
the clear asset to not swell anymore in any kind of solvent once they are polymerized. However,
their interpenetration within epoxy networks remains a challenge due to competitive chemical
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reactions. In particular, amines used for the crosslinking of epoxy networks are also able to
catalyse the ring opening polymerization of benzoxazine monomers, or even to react with them,
preventing thus the formation of clear IPNs. The following chapter deals with this topic, and
reports the preparation of IPN of CDGE network with a model polybenzoxazine network. A state-
of-the art of CDGE is first reported to introduce this topic.
1.1 Cashew nutshell diglycidyl ether
CDGE is a commercially available product, produced by Cardolite and supplied under the
trademark NC514 (Figure IV – 2). Researchers firstly focused on its molecular characterization
because of its wide molecular diversity. Indeed, as previously mentioned, cardanol is composed
of four molecules with a variable unsaturations rate. CDGE epoxy resin is obtained by the
phenolation of cardanol unsaturations through Friedel-Craft reaction and followed by the
epoxidation of the hydroxyl groups by reaction with epichlorohydrin.35
Figure IV - 2. Friedel-Crafts alkylation of phenol with cardanol (ideal reaction pathway).
Cardolite indicates an Epoxy Equivalent Weight (EEW) of 490 g/eq for the CDGE epoxy pre-
polymer and the chemical structure represented in Figure IV - 1.
The chemical structure of CDGE pre-polymer was fully characterized by NMR analysis,13 as well
as by size exclusion chromatography (SEC) and MALDI mass spectrometry.204, 212 The resulting
materials properties were also studied.
The NMR analysis of the CDGE pre-polymer allowed the determination of its unsaturation
composition. CDGE contains predominantly saturated chains (95 %) and mono-olefinic chains (5
%) as illustrated in Figure IV - 3.13
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Figure IV - 3. Chemical structure of diglycidyl ether of cardanol determined by 1H NMR
analysis.213
Furthermore, opened epoxy groups were also revealed, a ratio of 70 % of epoxy groups and 30 %
of opened epoxy rings were found to compose the CDGE compound (Figure IV - 4). The
experimental molar mass found by SEC for CDGE (1029 g/mol, polystyrene standard) is higher
than the theoretical molar mass of 460 g/mol indicated by Cardolite. The CDGE compound is thus
a mixture of epoxidized forms of cardanol. These results were moreover confirmed by the
demonstration of possible poly-substitutions of the phenolic ring during phenolalkylation.35 The
chemical structure of CDGE, based on the NMR and SEC analysis, is proposed in Figure IV - 4.
Figure IV - 4. Chemical structure of CDGE obtained from NMR analysis.213
Furthermore, four different structures, determined by MALDI mass spectrometry and depicted
in Figure IV – 5, were found to further compose the CDGE epoxy pre-polymer.204 CDGE was found
to be composed of epoxidized cardanol bearing an additional phenol moiety (Figure IV - 5a),
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epoxidized cardanol containing both an epoxidated and a native phenol on its side chain (Figure
IV – 5b), epoxidized cardanol linked to a native cardanol (Figure IV – 5c), and two epoxidized
cardanol linked by a native phenol (Figure IV - 5d).
Figure IV - 5. Additional chemical compounds composing CDGE determined by MALDI-MS
analysis a) epoxidized cardanol bearing an additional phenol moiety, b) epoxidized cardanol
containing both an epoxidated and a native phenol on its side chain, c) epoxidized cardanol
linked to a native cardanol, d) two epoxidized cardanol linked by a native phenol.204
The chemical structure of CDGE is thus very complex and composed of a significant number of
molecules. However, the lack of purification of this commercial product is not a drawback to its
use, and it is worthy to remind that even very commonly used BADGE pre-polymer (DER332) is
composed of oligomers and it is the reason why its reactivity is averaged and given in EEW.
1.2 CDGE-based thermosets
Jaillet et al. were first to study the elaboration of CDGE networks.213 They investigated the
optimum ratio between the epoxy compound and various amine hardeners, to determine the
corresponding materials with the higher glass transition temperature.
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CDGE epoxy materials were elaborated with isophorone diamine (IPD) and Jeffamine D400 as
crosslinking agents (Figure IV - 6). The corresponding materials were compared to BADGE/IPD
reference epoxy resin. Both crosslinking agents are aliphatic amines with a similar functionality,
but the inherent chemical structure of Jeffamine - composed of a moderate oxypropylene chain
(6.1 units) - leads to very flexible networks. Formulations with a ratio of 1/1 eq for BADGE/IPD
led to the material with the highest Tg of 158°C.
Figure IV - 6. CDGE cross-linking agents a) isophorone diamine and b) Jeffamine D400.
The most suitable ratio between CDGE and IPD was 1 g of CDGE and 0.13 g of IPD, leading to a
material with a Tg = 50 °C. The cardanol alkyl chains act as a plasticizer and soften the network.
When Jeffamine D400 was used in lieu of IPD, the best epoxy/amine ratio was 1 g of CDGE and
0.29 g of Jeffamine, yielding to a material with a very low Tg = 15°C. The CDGE network Tg is thus
highly affected by the Jeffamine diamine flexibility. These results were supported by the
determination of the networks crosslinking densities (ʋe) from the storage modulus at 60 °C
above the Tg, determined by DMA (Table IV - 1). The crosslinking density was calculated by the
following formula developed by Webster et al. 214:
E’ = 3ʋeRT
The lower crosslinking density of the CDGE/IPD network in comparison to the BADGE/IPD
network is explained by the higher flexibility and lower EEW of CDGE.
Epoxy/amine
(amine equivalent) Tg (°C)
E’ (MPa)
at Tg + 60 °C ʋe (103 mol/m3)
BADGE/IPD
158 19.6 4.8
CDGE/IPD
50 3.2 1
CDGE/Jeff400
15 2.6 1
Table IV - 1. Thermomechanical properties of CDGE cured with IPD or Jeff400, compared to
BADGE/IPD network.213
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Similar studies were undertaken by Chrysanthos et al.,212 who reported the elaboration of
CDGE/IPD networks and compared them to BADGE/IPD networks. Analogous results as in Jaillet
et al. were found for a formulation ratio of 1/1 (CDGE/IPD equivalent).
CDGE epoxy pre-polymer was also studied to substitute BADGE for the elaboration of epoxy
thermosets for adhesive applications.215 The adhesive and thermo-mechanical properties, as well
as the water resistance were studied for different compositions of BADGE/CDGE co-networks,
cross-linked with 1,2-diaminocyclohexane (DAC) (Figure IV - 7) in stoichiometric amount.
Figure IV - 7. Chemical structure of 1,2-diaminocyclohexane (DAC) cross-linking agent.
The main weakness of BADGE networks is their low water resistance, and a way to evaluate it is
to perform wet cataplasm tests. The adhesive properties and the water resistance of the
CDGE/DAC network were tested by these pull-off-tests on alumina after wet cataplasm swellings.
During these tests, the assemblies were exposed to water at 80 °C during 4 h and the adhesion
strength was measured after this exposition. Interestingly, neat CDGE/DAC epoxy network
displayed after this test a high adhesive strength (4.5 MPa), even higher than dry neat
BADGE/DAC network adhesion strength (4 MPa). Thus the more sensitive to water is the
network, the lower is the adhesion strength after wet cataplasm test. Indeed, higher strengths
were due to better surface wettability (Contact angles values obtained by elliptic calculation
method: 66 ± 2 °for BADGE and 51 ± 1 ° for CDGE) leading to stronger aluminium-epoxy joints.
These results are highlighting the interesting properties of CDGE-based materials to substitute
Bisphenol A diglycidyl ether in adhesive applications in wet environments. However, in spite of
this relatively high resistance to water, certainly linked to the very limited hydrolysis of CDGE
network compared to BADGE, CDGE swells too much in water. Even if the impact on the Tg is very
low, one can imagine that 5 % volume change would be problematic for a lot of applications. The
addition of fillers, like clay of expanded graphite, is a well-known approach that would limit the
diffusion of H2O molecules within the network. In this work, we decided to consider another
approach based on a macromolecular reinforcement. The following parts are focusing on the
state-of-art of the macromolecular reinforcement of epoxy networks, and more particularly on
the use of benzoxazine.
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1.3 Reinforcement strategies: macromolecular reinforcement of epoxy networks
Owing the high performance properties of polybenzoxazines, their use as reinforcement for the
cardanol-based epoxy material – CDGE - has been foreseen in the following chapter. Indeed,
polybenzoxazines materials are known to have excellent thermo-mechanical properties and high
stiffness. Their use as reinforcement of the epoxy network properties appears thus as a promising
opportunity. Nevertheless, despite the advantageous properties of polybenzoxazine materials,
their high brittleness and low cross-linking density, in comparison to epoxy thermosets for
example, are the major drawbacks of polybenzoxazine materials. The particular properties of
PBz are explained by the formation of strong H-bonding between the phenolic hydroxyl groups
and the tertiary amines of the Mannich linkages formed by ROP.129-132 Thus, to date, the majority
of the works reported on polybenzoxazine and epoxy resins aimed at the the improvement of the
flexibility of benzoxazine resins by co-reactions and co-crosslinking with epoxy resins.216
1.3.1 State of the art of the epoxy/benzoxazine based co-networks
In several recent works, co-networks between epoxy and benzoxazine resins have been reported
to successfully improve the thermal and mechanical properties of the resulting material. As
benzoxazine monomers are reactive towards amines, but also towards the epoxy groups
themselves, various strategies have been considered for the reinforcement of benzoxazines by
co-polymerization with epoxy resins.
1.3.1.1 Epoxy/benzoxazine
Ishida et al. 217 were first to report the preparation of PBz/epoxy co-networks by the reaction
between the epoxy groups and the phenolic hydroxyl group issued from the opening of the
oxazine ring (Figure IV - 8). In this work, BADGE was reacted with a bisphenol-A based
benzoxazine in weight proportion 30/70. An increase of the Tg (from 141 °C to 156 °C) was
observed due to the additional cross-linking density added by the benzoxazine molecules.
Figure IV - 8. Synthesis of Pbz/epoxy co-networks.217
This approach is nevertheless limited to systems containing a major part of benzoxazine. Indeed,
a too high amount of epoxy groups would lead to a decrease of the crosslinking density due to
unreacted or small molecular weight epoxy acting as plasticizer within the PBz resin. Similar
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results were obtained by Jain et al..218 The activation of the Bz ROP by the BADGE compound is
attested by the decreasing of the benzoxazine polymerization temperatures. Nevertheless, the Tg
was also found to decrease with an increase of the BADGE amount.
Interestingly enough, these systems were shown to be very stable at high temperature since the
polymerization was triggered by the oxazine ring opening that occurs around 150 °C for
bisphenol-A based benzoxazine. Based on this property, Kimura et al.219 developed a new epoxy
precursor from the combination of BADGE and PBz stable at elevated temperatures for injection
molding. The PBz cured BADGE thermoset displayed even a higher Tg (175 °C) than the BADGE
thermoset cured with novolac (phenol-formaldehyde resin, Tg = 149 °C).
Epoxy materials are generally cured with multifunctionnal amines, and it is conceivable to use
them in combination to benzoxazine.216, 220-227 Several reactions described hereafter are likely to
occur in these ternary systems, influencing the final material morphology and properties.
Benzoxazine monomers were shown to react with epoxy groups after their ring opening (Figure
IV – 8). In particular, benzoxazine monomers are reactive towards primary amines (Figure IV -
10) used to crosslink epoxy networks. Such a reaction occurring at low temperature, would lead
to a competition with the epoxy/amine cross-linking reaction (Figure IV – 9).
Figure IV - 9. Reaction between epoxy and primary and secondary amine functions.
1.3.1.2 Epoxy/amine/benzoxazine
Grishchuk et al. 216 investigated the effect of common diamines usually used as epoxy hardener,
such as diethylenetriamine (DETA) and 4,4’-diaminodiphenyl methane (DDM) on the
polymerization of a Bisphenol A/aniline Bz (BA-a). DSC analysis of BA-a revealed a single
exothermic signal with a maximum at Tp = 253 °C corresponding to the opening of the oxazine
ring. The addition of a diamine compound, whatever it is, led to the same trend as illustrated by
the shift of the exotherms to lower temperatures: the diamine triggers the opening of the oxazine
rings at lower temperatures.
Concerning this topic, a throughout study has been published by Endo et al. 228 describing the
effect of the chemical structure of a large set of diamines onto Bz polymerization. The hardeners
donate a proton to the benzoxazine monomer, resulting in an anion able to eventually attack the
electrophilic iminium intermediate. Clearly, the benzoxazine compound acts as a nucleophile
towards the proton in this case and the lone pair of the nitrogen of the oxazine ring is thought to
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be the most reactive position. Therefore, it is expected that a series of reactants can open the
oxazine ring via a nucleophilic attack to the electrophilic portion at the C8 carbon atom (Figure
IV - 10).
Figure IV - 10. Reaction scheme of opening the oxazine ring via an amine nucleophilic attack.229
The addition of an amine achieved a much faster polymerization at mild temperatures, and the
efficiency of the diamine onto the ROP of benzoxazine is directly depending on its basicity. The
authors of this work evidenced the following order: arylamine > alicyclic amine > alkylamine.
In summary, it is easy to expect that mixtures of epoxy /diamines /benzoxazines will all react
together if the curing is not controlled. Indeed, Wang et al. 227 evidenced that the morphology of
the networks may be affected by the curing process. The curing of a ternary system composed of
Bisphenol A-based benzoxazine, BADGE, and imidazole at 180°C led to the simultaneous reactions
of all the compounds together (epoxy/imidazole, Bz/imidazole, Bz/epoxy, and Bz
homopolymerization). By starting the reaction at a lower temperature (80 °C), the diamines
reacted first with the epoxy group leading first to the formation of the epoxy network, and
consuming all the epoxy and imidazole compounds. This first step was then followed by the
formation of the PBz network during the post-cure at 180 °C through the homo-polymerization
of the Bz monomers.
In consequence Wang et al. highlighted that the control of the curing conditions of
epoxy/diamine/Bz system could lead to the formation of a material mainly composed of two
distinguished structures: an epoxy-amine network and a polybenzoxazine network. These results
pave the way to the possible elaboration of IPN based materials between epoxy and Bz which will
be subsequently studied.
1.4 Epoxy/polybenzoxazine IPNs
Sperling defines IPNs as the combination of two, or more, polymer networks that are synthesized
in juxtaposition. According to the IUPAC, “an IPN is a polymer comprising two or more polymer
networks which are at least partially interlaced on a molecular scale, but not covalently bonded to
each other and cannot be separated unless chemical bonds are broken”.230
IPNs can be synthetized from two synthetic pathways: sequential synthesis or in-situ synthesis.
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In the sequential synthesis method, a first network is formed and subsequently swollen with the
reagents of the second network, which is then synthesized inside the first network (Figure IV -
11). By this method, the morphology is generally imposed by the first network, and the IPN
composition range is limited by the maximum swelling of the first network by the second network
reagents.
Figure IV - 11. Sequential synthesis of IPN.
In the in-situ method, all reagents are mixed at the beginning of the synthesis. The two network
formations can be, or not, started simultaneously (Figure IV - 12). It is necessary for the two
network formation mechanisms to be different and independent. Otherwise, a single polymer, or
copolymer network or a co-network is obtained. By this method, the ratio of the two networks
can be almost freely modified by adjusting the reagents proportions.
Figure IV - 12. In-situ IPN synthesis.
The two synthetic methods allow the association of cross-linked polymer networks of different
chemical nature. The properties and the morphology of the obtained materials can be adjusted
by modifying the partner proportions, the formation rates of each network compared with the
other, the thermo-dynamical phenomena driven the phase separation (before crosslinking) of
most polymers. Thus IPNs undergo phased separation, but at a smaller scale, than non-
crosslinked polymer blends. During polymerization and network formation, the polymer molar
weights increases, the mixture deviates from equilibrium, and demixing appears. The network
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formation opposes to the phase separation and thus the faster the network formation and the
smaller the obtained domains.
Phase separation in the polymer blends can occur according to two mechanisms, depending on
the temperature and composition of the mixture. First, in a nucleation/growth mechanism,
nodules of one of the two components are forms. These nodules increase with time and eventually
percolate during phase separation (Figure IV - 13).
Figure IV - 13. Nucleation and growth mechanism.
The spinodal decomposition mechanism is also possible. This mechanism produces materials in
which domains with a high concentration of one polymer are dispersed in a matrix with a high
concentration of the second polymer. It corresponds to a meta-stable system in which domains
with complex shapes appear. Chemical composition of these domains evolves with time; each
species becomes predominant in one of the domains with time. This mechanism creates a co-
continuity of the two phases that is also named as gyroïdal structure (Figure IV - 14).230
Figure IV - 14. Gyroïdal structure.
The phase separation mechanism depends on the proportion of the two polymers.
Nucleation/growth mechanism is favoured if one of the precursors is in low concentration. As the
concentration of this component increases a mixture of discrete nodules and complex domains
formed by spinodal decomposition are observed. If the two components are present in equal
amounts, phase separation often occurs by a spinodal decomposition mechanism and two co-
continuous phases are obtained.231
Thermosets can be reinforced at the macromolecular scale by blending with a second polymer or
by the formation of IPN. The IPN structure is considered as an interesting method for the
reinforcement of epoxy materials as the properties of the two polymers are combined in a novel
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material displaying ideally a single glass transition temperature, witnessing the close vicinity of
the two kinds of polymer chain. The single transition temperature, situated between the
transition temperatures of the single networks, corresponds to the interpenetrating phase.
Nevertheless, IPNs show usually two transition temperatures, corresponding to the two phases
induced by the polymer phase separation and enriched in one polymer network.
Epoxy materials are compatible with a wide range of thermoset polymers and are often co-
reactive. Epoxies have thus been blended with almost all the other families of polymers. Similarly,
numerous studies report the toughening of epoxy resins by the formation of IPNs with
polyurethane resins.232-235 Isocyanate-terminated polybutadienes,236 and polyesters,237 were also
considered for the improvement of epoxy properties.
IPNs were mainly used for the improvement of the elasticity, the brittleness or the adhesive
strength of epoxy networks, while maintaining their good thermal properties. To this aim, the
most commonly used polymers are polyurethanes 238 239 or bismaleimides.240 Their incorporation
within the epoxy thermosets allows the improvement of the materials flexibility and its thermo-
mechanical properties. Owing to their excellent thermo-mechanical properties and high stiffness,
polybenzoxazines could be used similarly to polyurethanes and bismaleimides to reinforce CDGE.
The poly(CDGE) single network crosslinked by DAC was shown to display low Tg at 40 °C and a 4
GPa storage modulus in the glassy state.215 Furthermore, Verge et al. reported the high water
uptake of 6 ± 0.2 wt% of a poly(CDGE) network with DAC as hardener, most probably due to its
wide network meshes. On the contrary, the single poly(EDBz) network was shown to display
relatively high Tg of 216 °C and high modulus (6-7 GPa). Furthermore, PBz materials are well-
known for their very low water uptake.115 In consequence, the elaboration of
poly(CDGE)/poly(EDBz) IPN was foreseen as a strategy to reinforce the properties of the
poly(CDGE) network, while preventing the water diffusion by the presence of the poly(EDBz)
network.
This chapter relates the elaboration of interpenetrating polybenzoxazine and epoxy/diamines
networks. By this strategy, we expect to tackle the main issue from CDGE networks, i.e. the water
uptake. Indeed, we envision that the “filling” of the wide mesh of the cardanol-based network by
a PBZ prevent the water diffusion, in addition of clear reinforcement of the thermal and
mechanical properties of the materials. As above mentioned, many competitions may occur
within ternary benzoxazine/epoxy/amines systems and suitable conditions for the elaboration
of IPN have to be found. They are detailed in the following paragraphs.
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2 Results and discussion
The detailed experimental conditions are reported in annex p 181.
2.1 Choice of the system
2.1.1 Sequential in-situ preparation of IPN
First of all, the choice of the IPN elaboration method is in part determining the choice of the
various reagents. In the present study, the choice of the reagents and the curing conditions will
be investigated with the aim to tend toward the in-situ sequential IPN synthesis method. Indeed,
by this synthesis way, the ratio of the two networks can be almost freely modified by adjusting
the reagents proportions, allowing the study of the materials properties depending on their
composition.
With the aim to elaborate IPN materials by in-situ sequential synthesis, the expected reactions
are depicted in Figure IV – 15a.
Figure IV - 15. a) Expected reactions during the IPN sequential in-situ synthesis, b) in-situ
sequential synthesis of a poly(CDGE)/poly(Bz) IPN material.
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As it can be observed, two distinct reactions will be favoured for the in-situ sequential IPN
elaboration. In a first time the polymerization of the epoxy-amine network (poly(CDGE)) between
CDGE and the suitable diamine hardener is expected, followed in a second time, by the ring-
opening polymerization of the Bz monomer forming the polybenzoxazines network. It is
important to notice that any possible reaction between the Bz monomer and the diamine
hardener is to avoid, leading otherwise to co-networks. The choice of a diamine hardener non-
reactive towards the Bz monomer is thus to favour. Furthermore, it is well-known that Bz
monomers polymerize at high temperatures, in the range of 200 °C to 220 °C. In consequence, the
elaboration of the IPNs through the in-situ sequential synthesis is only possible if the epoxy-amine
system cures at low temperature, whereas the PBz network cures at elevated temperature.
Moreover, the possible reaction between amines and Bz monomers have to be similarly avoided.
In conclusion, the choice of the diamine hardener is fundamental for the elaboration of
poly(CDGE)/poly(Bz) IPNs. To this aim, the curing of CDGE with various diamine hardeners has
been investigated by DSC analysis, as well as the curing of the Bz monomer in presence of the
selected diamine.
2.1.2 Determination of the Bz monomer
As described previously, it is essential to control the competition reactions which may occur
between benzoxazines, epoxy and amine compounds in order to elaborate IPNs. For this reason,
the suitable conditions for the elaboration of IPN between CDGE and benzoxazines are studied in
the following chapter. A benzoxazine model molecule synthetized from phenol, ethylenediamine
and paraformaldehyde, (EDBz, Figure IV - 16) has been selected in order to avoid any likely
additional side-reaction from benzoxazines substituents or functional groups.
Figure IV - 16. Chemical structure of the EDBz model Bz monomer.
Miscibility tests were achieved between the CDGE and the EDBz compounds. The two compounds
were miscible and no demixion appeared even after several days.
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2.1.3 Determination of the suitable di-amine hardener
The choice of the diamine hardener used for the polymerization of the CDGE is essential for the
elaboration of IPNs. In order to avoid the formation of polymer co-networks, a diamine non-
reactive towards the EDBz monomer and allowing the curing of CDGE at low temperature will be
needed.
In order to find a suitable hardener for the epoxy system, various diamine compounds were
tested by the following procedure: The CDGE was heated at the EDBz monomer melting
temperature (Tm = 116 °C for EDBz). The amine hardener was then added to the mixture in
stoichiometric amount to the CDGE compound. The blend was stirred at Tm until a homogeneous
mixture was obtained. The reaction mixture was then studied in function of the temperature by
DSC analysis.
DSC thermograms of CDGE cured with different diamines are reported on Figure IV – 17. As a
comparison, the curing of the EDBz monomer is also reported.
Figure IV - 17. Curing conditions of CDGE with various diamine compounds monitored by DSC
analysis (N2, 20 K/min), compared to the curing conditions of the EDBz monomer (Dashed
curve, (N2, 20 K/min)).
Different curing behaviours, depending on the diamine hardener are observed by DSC analysis.
Even though the curing onset is situated around 50 °C, independently of the diamine hardener,
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the curing peaks width are differing. In the presence of diethylenetriamine (DTA) and m-
xylenediamine, the exothermic peaks are rather thin and ranging from 50 °C to around 150 °C. In
the case of isophorone diamine (IPD) as hardener, the exothermic peak is boarder ranging from
50 °C to around 175 °C. Finally, when Jeffamine EDR 148, trans-1, 4-diaminocyclohexane, or
Jeffamine EDR 176 are used as hardener, very broad exothermic peaks are observed ranging from
50 °C to over 200 °C, overlapping the ROP temperature of the EDBz monomer.
As we aim at finding an epoxy-amine system curing at low temperature, the DTA, m-
xylenediamine, and IPD hardener are the most suitable. Nevertheless, as described above, the
diamine hardener is added to the CDGE/EDBz mixture at elevated temperature (T > 116 °C). A
diamine hardener with a high boiling temperature is needed, in order to avoid any evaporation
during the addition step to preserve the stoichiometric amount between the diamine compound
and CDGE. DTA and DAC display the lowest boiling temperatures: Tb = 199 – 209 °C and Tb = 197
°C respectively. In consequence, the isophorone diamine (IPD; Tb = 247 °C) appears as the most
suitable hardener for CDGE in the elaboration of IPNs.
In order to confirm the suitability of IPD as hardener for the elaboration of IPNs, the curing of the
EDBz monomer was monitored by DSC in the presence of one equivalent of diamine hardener
(data not showed). The DSC analysis corresponding to the curing of EDBz in presence of IPD
evidenced the absence of exothermic peak in the range from 0 °C to 200 °C, indicating that the
EDBz monomer did not react with IPD within this temperature range. Only an exothermic peak
starting around 200 °C can be observed, probably corresponding to the EDBz ring opening. In
conclusion, the DSC monitoring of the EDBz curing in presence of IPD confirms that IPD could be
a suitable hardener of the CDGE network without reacting with EDBz at rather low temperature
and furthermore without influencing on the EDBz ROP at elevated temperature.
These preliminary results were further confirmed by the DSC analysis of the CDGE/IPD/EDBz
ternary system (Figure IV - 18). The DSC analysis of the ternary system curing was then
compared to the curing of the reference network CDGE/IPD and the curing of EDBz respectively.
The particular case of an expected IPN in 60 wt% CDGE and 40 wt% EDBz (named CDGE/EDBz
60/40) was chosen for the DSC monitoring. The IPD hardener was added in stoichiometric ratio
to CDGE.
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Figure IV - 18. Curing conditions of various systems a) CDGE with IPD, b) EDBz and c) 60/40
CDGE/EDBz with IPD monitored by DSC analysis (N2, 20 K/min).
The DSC thermogram of the CDGE/EDBz system, displayed on Figure IV - 18, indicates the
possible formation of IPNs between CDGE and EDBz. Indeed, when comparing the thermograms
of CDGE and EDBz, it can be observed that the formation of the two networks can be
differentiated. The formation of the neat poly(CDGE) network with IPD (Figure IV - 18, a) occurs
at rather low temperature, as an exothermic peak is displayed in the range of 50 °C to 170 °C. The
formation of the neat poly(EDBz) network (Figure IV - 18, b) occurs at elevated temperature,
indicated by the presence of an exothermic peak corresponding to the EDBz ROP starting around
200 °C. Finally, the DSC thermogram of the ternary system (CDGE/IPD/EDBz) (Figure IV - 18, c)
confirms the formation of sequential networks. Indeed, a first exotherm is observed from 50 °C
to 200 °C, corresponding to the polymerization between CDGE and IPD, followed by a second
exotherm observed from 200 °C to 250 °C, corresponding to the EDBz ROP. In consequence, the
elaboration of an IPN structure can be assumed according to this DSC monitoring.
In conclusion, the formation of the first poly(CDGE) network by reaction between CDGE and IPD
should be achieve at low temperature, followed by the formation of the second poly(EDBz)
network at high temperature. By default, the CDGE monomer will always be reacted with IPD in
stoichiometric ratio. Consequently, in the following paragraphs, in order to facilitate the materials
denomination, the CDGE/IPD system will be noted CDGE (unreacted mixture of CDGE and IPD)
and the crosslinked network will be noted poly(CDGE) (crosslinked CDGE/IPD network).
Similarly, crosslinked network issued from EDBz will be noted poly(EDBz).
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2.2 Curing profile for the elaboration of poly(CDGE)/poly(EDBz) IPNs
To insure the successive elaboration of the two networks, a multiple step curing profile was
applied to the monomers mixtures. The model case of a 60/40 (CDGE/EDBz) system was also
used for this study. First, the elaboration at low temperature of the poly(CDGE) network is
favoured, resulting in a first step cure at 100 °C during 16h. The temperature of 100 °C is chosen
with the aim to allow the epoxy-amine polymerization. Furthermore, the CDGE compound plays
the role of a solvent for EDBz and a temperature of 100 °C is sufficient to keep the EDBz compound
in a molten state. The curing of the EDBz monomer is then triggered at moderate temperature by
a first cure at T = 160 °C during 1h followed by 2h at T = 180 °C, in order to avoid a too rapid
gelation of the system. The post-cure of the poly(EDBz) network is finally achieved after 2h at
200 °C and 30 min at 220 °C (Figure IV - 19).
Figure IV - 19. Curing conditions of CDGE/EDBz (60/40 % wt) systems.
The successive formation of the networks can be demonstrated by quenching the curing at the
assumed end of the poly(CDGE) network formation, i.e. after 16 h at 100 °C. DSC analysis of the
partially (i.e. after 16 h at 100 °C) and of the totally cured poly(CDGE)/poly(EDBz) (60/40)
system (at the end of the thermal treatment) were carried out to confirm the sequential network
formation and their total cross-linking. To further validate the curing conditions, soluble fractions
of the samples were extracted with chloroform after the first curing step and on the final material.
The DSC analysis and the solvent extraction were achieved in order to estimate the amount of
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unreacted CDGE or EDBz monomers. The extracted content (EC) was given as a weight
percentage:
EC (%) = (𝑊𝑖−𝑊𝑒)
𝑊𝑖 x 100
Where 𝑊𝑖 and 𝑊𝑒 are the weights of the samples before and after extraction, respectively.
2.2.1 First step curing
2.2.1.1 Evaluation of the poly(CDGE) formation
The DSC of the poly(CDGE) reference material, without EDBz, after the first cure of 16 h at 100
°C, is displayed in Figure IV - 20.
Figure IV - 20. DSC analysis (N2, 20 K/min) of the poly(CDGE) material (without EDBz) after the
first curing step of 16 h at 100 °C.
The thermogram of the poly(CDGE) network, without the EDBz monomer,after the first curing
step at 100 °C during 16 h, displays a slight exothermic peak around 175 °C, indicating that the
CDGE curing is probably not entirely achieved. The enthalpy of ΔH = 2.5 J/g indicates that a minor
amount of CDGE has not polymerized after the first curing step when comparing to the
polymerization enthalpy needed to fully cure the system (ΔH = 112.8 J/g). The reaction progress
is thus estimated to be achieved at 98 %. This result is comforted by the low extractible content
of 7 ± 5 % after solvent extraction in CHCl3. In conclusion, the poly(CDGE) network is almost
achieved after 16 h at 100 °C, and the low enthalpy and the low extractible content were
considered as very acceptable for the IPNs elaboration conditions.
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2.2.1.2 Evaluation of poly(EDBz) formation
The CDGE system was then crosslinked in presence of EDBz monomer in order to verify that EDBz
does not interact in the formation of the poly(CDGE) network. The corresponding DSC
thermogram after the first curing step of 16 h at 100 °C is displayed in Figure IV - 21.
Figure IV - 21. DSC analysis (N2, 20 K/min) of the poly(CDGE)/EDBz (60/40) system after the
first curing step of 16 h at 100 °C, and compared to neat poly(CDGE) after 16 h at 100 °C.
As expected, the DSC thermogram of the poly(CDGE)/EDBz (60/40) system displays an
exothermic peak starting around 175 °C, corresponding to the ROP of the EDBz monomers. This
peak confirms that un-reacted EDBz monomers are present in the material after the first curing
step. The formation of the poly(EDBz) network will thus be achievable since it has still not
reacted. These results are corroborated by the enthalpy of ΔH = 17.2 J/g of EDBz, very close to
the polymerization enthalpy of the single EDBz network (ΔH = 17.9 J/g of EDBz). Furthermore,
no exothermic peak relative to the CDGE polymerization reaction is visible, further confirming
the formation of a first poly(CDGE) network during the first curing step, without involving the
EDBz monomers. These results were further confirmed by the extractible content obtained for
the poly(CDGE)/EDBz (60/40) system after the first curing step. Indeed, 38.5 ± 5 % of extractible
content were obtained after 72 h solvent extraction in CHCl3, confirming that almost all the EDBz
monomers remain unreacted during this first curing step as 40 wt% of EDBz are present in the
starting system.
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2.2.2 Full curing profile
Finally, DSC measurements and solvent extractions were performed (Figure IV - 22) on fully
cured poly(CDGE)/poly(EDBz) (60/40) material (curing program: 1 h at 160 °C, 2h at 180 °C, 2 h
at 200 °C and 30 min at 220 °C).
Figure IV - 22. DSC analysis (N2, 20 K/min) of the poly(CDGE)/poly(EDBz) (60/40) material
after the full curing program (1 h at 160 °C, 2 h at 180 °C, 2 h at 200 °C and 30 min at 220 °C).
As expected, no exothermic peaks are observed. This absence of exothermic peaks reveals the
total cure of both networks after the full curing program applied to the materials. Furthermore,
the 0 % extractible contents found for 60/40 poly(CDGE)/poly(EDBz) corroborate the DSC
results.
In conclusion, it can be deduced that the selected curing program is suitable for the elaboration
of IPN materials between CDGE and EDBz. The following part focuses on the CDGE/EDBz
monomers ratio onto the properties of the final materials.
2.3 Poly(CDGE)/poly(EDBz) IPNs
2.3.1 Poly(CDGE)/poly(EDBz) IPN Material elaboration
The reference materials from EDBz and CDGE, as well as the IPN materials with various
compositions, were elaborated by first mixing the CDGE compound and the EDBz compound at
100 °C and degasing during 1 h at 100 °C, followed by the addition of the IPD hardener in
stoichiometric ratio to the CDGE monomer. The mixtures were then transferred to a U-shaped
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mold. The previously determined curing program of 16 h at 100 °C, 1 h at 160 °C, 2 h at 180 °C, 2
h at 200 °C and 30 min at 220 °C was applied to each material.
IPNs with different EDBz contents ranging from 20 % to 80 % by weight were synthetized, while
keeping the same ratio between CDGE and the IPD hardener. All investigated CDGE/EDBz
compositions are reported in weight-by-weight ratio. Thus, an IPN obtained from a mixture of
0.80 g of CDGE and 0.20 g of EDBz will be noted as poly(CDGE)/poly(EDBz) (80/20) IPN.
2.3.2 Thermo-mechanical properties of IPN materials
The thermo-mechanical properties of poly(CDGE)/poly(EDBz) IPNs were studied by DMA
analysis and displayed on Figure IV - 23. For the sake of comparison, the two single networks
poly(EDBz) and poly(CDGE) were also elaborated using the same curing conditions and
characterized by DMA.
Figure IV - 23. Evolution of the storage modulus E’ of poly(CDGE)/poly(EDBz) IPNs (80/20,
70/30, 60/40, 50/50, 40/60, 30/70 and 20/80) as a function of temperature, obtained by DMA
(Tension mode with 0.05 % strain, 1 Hz and 3 °C/min).
The poly(CDGE) network is characterized by an α-relaxation centered at Tα = 50 °C and a storage
modulus in the glassy state about 400 MPa. The poly(EDBz) network is in a glassy state up to 150
°C with E’ around 6 to 7 GPa and displays a Tα of 216 °C (Figure IV – 23 and Figure IV – 24).
As far as IPN are concerned, all the IPN materials are in a glassy state below 50 °C, as observed on
the DMA curves of the poly(CDGE)/poly(EDBz) networks. With increasing the temperature from
50 °C to 175 °C, the storage modulus of the IPN materials decreased, which indicate the materials
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softening. Furthermore, the values of the storage moduli were strongly impacted by the IPN
composition. Indeed, in this temperature range, it can be observed that the storage modulus
increased with weight proportion of the EDBz compound (arrow in Figure IV - 23). For instance
at 150 °C, the storage modulus increases from 9 MPa to 1600 MPa for the 80/20 and 20/80 IPN
materials respectively (containing 20 % and 80 % weight proportion of EDBz respectively).
Above 180 °C the storage modulus of the various IPN materials decreases again due to the
mechanical relaxation of the poly(EDBz) rich phase. As expected, an improvement of the
poly(CDGE) network thermo-mechanical properties is observed when combining it with a
poly(EDBz) network in an IPN structure.
Thermomechanical properties give a picture of local dynamic of polymer chain. As described
above when the two kinds of polymer chains are in close vicinity their dynamic influence each
other which results in only one mechanichal relaxation at a unique Tα. Hence the IPN present no
phase separation at the DMA scale. In the present case, for three IPN compositions with high CDGE
content – 80/20, 70/30 and 60/40– only one transition can be observed (Figure IV- 24).
Figure IV - 24. Evolution of the storage modulus E’ and tanδ of poly(CDGE)/poly(EDBz) IPNs
(80/20, 70/30 and 60/40) as a function of temperature, obtained by DMA (tension mode with
0.05 % strain, 1 Hz and 3 °C/min).
A lone mechanical relaxation around 70 °C is observed for these materials, close to the mechanical
relaxation of single poly(CDGE) as it is the main component of those IPNs. As no additional
transition corresponding to a poly(EDBz) rich phase is observed at higher temperature, it can be
assumed that the poly(EDBz) is entangled at nanometer scale within the poly(CDGE) network.
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When comparing to the neat poly(CDGE) network, an increase of the materials storage modulus
and Tα were observed by DMA analysis. The 80/20, 70/30 and 60/40 poly(CDGE)/poly(EDBz)
materials could thus be determined as materials composed of the first formed poly(CDGE)
network probably reinforced by poly(EDBz) network.
Contrary to these three IPNs, two mechanical relaxations are observed for the other compositions
from 50/50 to 20/80, like it can be observed on the curves displaying the tanδ values versus the
temperature (Figure IV - 25). Phase separation, even if it is fairly limited, occurs. For each IPN
material, the first mechanical relaxation located around 40 to 50 °C is associated to the
poly(CDGE) phase relaxation, while the second relaxation situated around 200 to 220 °C
corresponds to the poly(EDBz) phase.
Figure IV - 25. Evolution of the tanδ of poly(CDGE)/poly(EDBz) IPNs (50/50, 40/60, 30/70 and
20/80) as a function of temperature, obtained by DMA (tension mode with 0.05% strain, 1Hz
and 3°C/min).
All the IPN materials ranging from 50/50 to 20/80 are displaying complex phase morphology, as
evidenced by two distinct mechanical relaxations. In order to determine the domains
structuration of the two polymer phase, mechanical model developed primarily for polymer
blend have been tentatively used.
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2.3.3 Estimation of the morphology by theoretical models
The determination of the IPN materials morphology is very important in order to relate it to the
materials properties. Despite several characterization attempts, particularly through AFM in
tapping mode or elementary EDX-SEM analysis, we remained unable to determine the
morphology of the poly(CDGE)/poly(EDBz) IPN materials when phase separation occured.
Consequently, with the aim to obtain an estimation of the materials morphology, a comparison
between the IPN materials experimental thermo-mechanical data and those of theoretical models
were achieved. Indeed, IPN can be multiphase systems for which the storage modulus obtained
by DMA can be correlated to their composition and morphology. Several theories have been
developed to this aim. Most of the theories consider a macroscopic isotropy of the systems and a
perfect adhesion between the different phases.
Kerner described a model for a matrix in which spherical inclusions are dispersed over the whole
composition range.241 As this model does not take into account the interactions between the
dispersed inclusions and the continuous matrix, it predicts accurately the polymers blend
properties when the volume of the dispersed phase is low.
The material shear modulus G is defined as follow:
𝐺
𝐺1 =
(1−ɸ2)𝐺1+(𝛼+ɸ2)𝐺2
(1+𝛼ɸ2)𝐺1+ 𝛼(1−ɸ2)𝐺2
Where 1 is the continuous phase and 2 is the dispersed spherical inclusions, G is the shear
modulus, ɸ2 is the volume fraction of the inclusion spheres, and α is a function of the matrix
Poisson ratio according to the following equation:
𝛼 =2(4 − 5𝜈)
(7 − 5𝜈)
Where ν is the Poisson’s ratio.
A model which predicts a phase inversion at middle-range composition was predicted by
Budiansky.242 In the first case, the material is formed by a continuous phase 1 in which a second
phase – 2 - is dispersed as long as the volume fraction ɸ2 of the second phase is lower than 0.5.
When ɸ2 is higher as 0.5, a phase inversion occurs and the phase 2 becomes continuous with
phase 1 being dispersed within it. For this model, the shear modulus G observes the following
equation:
ɸ1
1+ɛ(𝐺1𝐺
−1) +
ɸ2
1+ɛ(𝐺2𝐺
−1) = 1
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Where ɛ = 2(4−5𝜈)
15(1−𝜈) ,
and ν is the Poisson’s ratio of the blend calculated using a combination of mixing, G the shear
modulus, and ɸi is the volume fraction of each component polymers.
Unlike the two previous models, Davies reported a model taking into account the interactions
between the two polymer phases in which both phases are co-continuous over the whole
material.243 In this particular case, the shear modulus G is expressed as:
𝐺1/5 = ɸ1𝐺11/5 + ɸ2𝐺2
1/5
As a reminder, these three models have rather been developed for the mechanical properties of
polymer blends. Nevertheless, numerous authors report their use for the description of IPNs
viscoelastic properties.244, 245 These models were shown to give an idea of the materials
morphology.
The modulus values calculated from the three aforementioned models, as well as the
experimental data of the poly(CDGE)/poly(EDBz) IPN materials, are reported on the Figure IV -
26. The models and materials modulus are reported versus their EDBz volume content. The shear
moduli (G’) of the poly(CDGE)/poly(EDBz) IPN materials were determined by the E’ and tanδ data
measured by DMA analysis as follow:
𝐸 = 𝐸′
cos (𝛿)
and
𝐺′ =𝐸
2∗(1+𝜈)
As models assume mixing of a hard and a soft polymer, the values of E’ and tanδ were taken at
140°C (poly(CDGE) in elastic state and poly(EDBz) in glassy state). In consequence, the Poisson’s
coefficients of rubbery poly(CDGE) and glassy poly(EDBz) networks are equal to 0.50 and 0.33
respectively. The Poisson coefficient of the IPN materials is calculated as the volume average of
those of the both component, depending their composition by the following formula:
𝜈 = ((0.50 ∗ 𝐶𝐷𝐺𝐸 𝑣/𝑣%) + (0.33 ∗ 𝐸𝐷𝐵𝑧 𝑣/𝑣%))
The shear moduli of the IPN materials were then compared to the calculated values obtained by
the three models.
It is important to notice that the models are employed for materials which display two transitions
on their DMA analysis as it is the case for poly(CDGE)/poly(EDBz) IPN with compositions ranging
from 50/50 to 20/80. Nevertheless, in the present case, for three IPN compositions with high
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CDGE content – 80/20, 70/30 and 60/40 – only one transition can be observed (Figure IV- 26)
and they will therefore not be discussed in relation to the models.
Figure IV - 26. Shear modulus of poly(CDGE)/poly(EDBz) IPN materials versus EDBz volume
fraction compared with modulus-composition models.
As it can be observed on the Figure IV - 26, the IPN shear moduli correlates closely the Davies or
Budiansky model for the IPNs from 50/50 to 20/80. Furthermore, the morphology of the IPN
materials is directed by the chemistry reactions that are occurring during the IPN elaboration.
Indeed, the first formed network is necessarly continuous.246 The poly(CDGE) network is thus
continuous. This is not in accordance with the Budiansky model whereas it is with Davies model
that consideres the second formed network as also continuous. Therefore, the IPNs of the studied
range could thus be considered as two co-continuous phases. Therefore, poly(CDGE)/poly(EDBz)
IPNs whether they are homogeneous at the DMA scale or co-continuous phase separated have
mechanical properties that are averaged by the volume proportion of polymers. The IPN
morphology is adequate for combination of both polymer properties, i.e. PBz network should
efficiently prevent the water diffusion, in addition of clear reinforcement of the thermal and
mechanical properties of the materials, whatever their composition.
2.3.4 Behaviour toward water exposure
In order to verify that the introduction of poly(EDBz) in IPNs is a viable strategy to prevent the
water diffusion within the material, swelling tests were achieved and monitored by DSC analyses.
The poly(CDGE)/poly(EDBz) IPN materials – varying from 80/20 to 20/80 in ratio – as well as
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the poly(CDGE) and poly(EDBz) single network were swollen in water during 15 days at 80 °C. It
was not possible to estimate the amount of water uptake from simple weight measurements
because the weight of the swollen samples was to low and the uncertainty of the measures were
thus to high. In consequence, the swelling behaviour of the materials was determined from the
melting enthalpy of water trapped in the material by DSC analysis. The melting point depression
study was followed in the present case. The heating of the swollen materials from -50 °C to 20 °C
at 5 k/min was observed.
The DSC curves during heating of the water swollen IPN materials and single networks are
displayed in Figure IV - 27.
Figure IV - 27. DSC thermograms of poly(CDGE)/poly(EDBz) IPNs (80/20, 70/30, 60/40,
50/50, 40/60, 30/70 and 20/80) and poly(CDGE) and poly(EDBz), during the heating of
swollen materials (N2, 5 K/min).
First of all, it is important to notice that depending on the IPN composition, different phase
transitions were observed. No endothermic peak is observed on the DSC curve relative to water
melting in the single poly(EDBz) network. Indeed, PBz resins are well-known for their very low
water uptake.120 On the contrary, the poly(CDGE) epoxy network was reported to display a high
water uptake, as verified by the presence of a bulk-water melting endothermic peak around 0 °C
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(ΔH = 27.31 J/g). When adding EDBz to the poly(CDGE) network a clear evolution can be
observed. A second endothermic peak shifted to around -10 °C is readily observed. The following
attribution of the endothermic peaks were hypothetized based on the work related by Wirtz et
al..247 The transition at higher temperature (around 0 °C) is related to the melting of the bulk
water contained in pores or cavities of the materials. The melting endotherm at lower
temperature (around -15 to -10 °C) represents the phase transition of the water confined in the
poly(CDGE) network, as water can form hydrogen-bonds with hydrophilic groups of such a
polymer.248
It corresponds to a confined water melting endotherm, and seems to be related to the presence
of poly(EDBz) network. A fraction of trapped water in close vicinity of polymer chains does not
behave as bulk water, propably beacause of reduced water domain’s size. It is furthermore
important to notice that with increasing amount of poly(EDBz) resin, the enthalpy of the
endothermic peak around 0 °C, attributed as the bulk-water melting peak, is varying from ΔH =
27.31 J/g (poly(EDBz) = 0 wt %) to ΔH = 0.22 J/g (poly(EDBz) = 40 wt %). In addition, the
enthalpy of the endothermic peak around -10 °C is also decreasing with increasing amount of
poly(EDBz). A threshold is reached at 40 wt % of poly(EDBz). Indeed, melting enthalpy at -10°C
related to confined-water becomes higher then that the melting enthalpy of bulk-water at 0°C.
IPN water uptake allows probing the IPN hydrophobicity since above 40 wt % of poly(EDBz) in
the IPN almost no bulk-water domains are anymore detected and the absorbed water molecules
are confined with the polymer chain and decreases gradually as the amount of poly(EDBz) within
the IPN increases. As a result, the global water uptake of the IPN materials is deacreasing with
increasing amount of EDBz.
In conclusion, the introduction of poly(EDBz) network within the poly(CDGE) network reduces
the water uptake of poly(CDGE) with increasing amount of poly(EDBz), while improving their
thermo-mechanical properties. Furthermore, an unexpected behaviour was also observed.
Indeed, PBz networks are known to have very low water uptake, but it seems that by the
elaboration of IPNs with the poly(CDGE) network, the PBz based IPN could be able to be swollen,
which could be an interesting application of these new IPNs. Nevertheless, further
characterizations are needed in order to confirm the observed results.
3 Conclusion
Diglycidyl ether of cardanol (CDGE) is a difunctionnal epoxy molecule that could interestingly and
advantageously substitute diglycidyl ether of BPA (BADGE) in applications such as coatings.
Indeed, CDGE has better adhesion properties than BADGE in addition to its non-carcinogenic
properties compared to BADGE. However, CDGE suffers from a relatively high swelling in water -
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due to its very low cross-linking density- , and is thus not suitable for almost all the coatings
applications. A way to tackle this issue is to reinforce at the macromolecular scale by the
formation of interpenetrating polymer networks (IPN) with polybenzoxazine.
The aim of the chapter was to prove the feasibility of the elaboration of IPNs between the
poly(CDGE) and the poly(EDBz) networks. Many chemical reactions can compete during the
formation of such a material, since benzoxazine monomers are able to react both with epoxies
and with hardeners used to commonly crosslink epoxies. Among the long list of tested diamines
isophorone diamine (IPD) appears to be a very good candidate. Indeed, in CDGE/EDBZ mixtures,
IPD only reacts with CDGE when moderate curing conditions are applied (100 °C during 16
hours). DSC measurements and solvent extractions in chloroform evidenced that 97 % of EDBZ
did not react during this first step and can thus still be interpenetrated within poly(CDGE) after a
second thermal treatment at higher temperature (1h at 160 °C, 2 h at 180 °C, 2 h at 200 °C and 30
min at 220 °C).
Compositions of the IPN were adjusted by screening the ratio between EDBZ and CDGE. DMA
characterizations highlight the formation of IPN for the 80/20, 70/30 and 60/40 compositions as
a lone Tg is observed (76.6 °C, 72.7 °C and 71.8 °C, respectively). As expected, storage moduli
increase while increasing the content of EDBZ, from 400 MPa for neat CDGE, 9000 MPa for 50/50
materials and about 13000 MPa for 20/80 materials, for instance (T = 25 °C).
Theoretical models were used to identify the morphology of the two phases IPN. These theories
are based on the evolution of the storage moduli of the materials as a function of their
composition. Experiment fits in very high accordance to the Davies model. According to this
theoretical model and to the occurring chemistry reactions, a co-continuous matrix should be
obtained for the systems with EDBz content above to 50 %. In spite of numerous attempts (atomic
force microscopy, scanning electron microscopy), it was not possible to observe these
morphologies and up to now the viability of this model is not confirmed.
Finally, swelling tests in water at 80 °C were performed on all the set of materials (i.e. with EDBz
content ranging from 0 to 100 wt %). Interestingly, it was observed that the incorporation of
poly(EDBz) leads to a significant drop of the swelling of poly(CDGE) in water. Evolutions of the
melting enthalpies of water were recorded on the swollen samples by differential scanning
measurements, as this method is very sensitive. Two endotherms of melting were observed at 0
°C and -10 °C depending on the materials composition, corresponding respectively to bulk- and
confined-water within the networks. In neat poly(CDGE) networks, water molecules are free,
with a melting enthalpy of 27.31 J/g. Increasing poly(EDBz) content leads to a confinement of the
water molecules, and to a decrease of the total melting enthalpy.
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In conclusion, it was demonstrated in this chapter that obtained IPN from CDGE and EDBZ is
possible through a suitable choice of the diamine hardener and of the curing conditions. Materials
with interesting properties were obtained, as their behaviour toward water is highly affected by
the poly(EDBz) content. These results were just obtained with a model – simple- benzoxazine
monomer to prove the feasibility of the concept. As it was shown in the third chapter, the chemical
design of benzoxazine monomers is versatile, and it could be easily envisioned that other
molecular architecture could be built by using other Bz monomers. Clearly, asymmetric
monomers with a cardanol moiety could be a major tool to tailor the morphology and properties
of the resulting IPN.
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General Conclusion and Perspectives
As mentioned all along the manuscript, the development of polymeric materials from natural and
renewable resources has attracted tremendous concern. Among the large variety of biomass-
derived compounds, cardanol through its inherent properties, has attracted our attention.
Throughout this thesis we have studied the potential of using cardanol as versatile chemical
platform to conduct different chemical transformation with the aim to find high add-value
applications for this underutilized product. We particularly focused in all our studies on the
control of the materials properties by the tuning of their chemical structures.
The first study described in this manuscript was the development of three cardanol-based
ammonium surfactants, and their potential as oraganomodifier for clays to enhance the
dispersion in composite materials. A particular focus was given to the reactivity of these
surfactants toward Monmorillonite clay (MMT) and epoxy resin. Three surfactants bearing
different amine reactive functionalities were obtained. The organomodification by cationic
exchange of MMT layers was effective using the three cardanol-based surfactants as evidenced
by XRD and MALDI-TOF/MS analyses. The increased interlayer distances between the clay
platelets were however found to be roughly similar due to the close chemical structure of the
surfactants. After the exfoliation, the content of amine functionality availlable (able to further
react with epoxy groups) of each surfactant was verified by grafting of furfuryl glycidyl ether and
further quantified by MALDI-TOF/MS analysis. Clay mineral-based polymer (CPN) with
conventional diglycidyl ether of bisphenol A were then prepared with the three O-MMT. As
expected, The XRD analysis and SEM observations coupled with energy dispersive X-ray analyses
revealed that the surfactant reactivity towards epoxies influences the clay dispersion. Indeed, for
the clay modified by the surfactants with lower available amine functionalities, only an
intercalated structure could be evidenced. Oppositely, the exfoliation of the clay layers was clearly
favoured by the clay modified by the surfactant displaying the higher content of amine
functionality as no diffraction peak could be observed on the corresponding XRD diffractogram.
In the chapter 3 we highlighted in a first stage the synthesis and characterization of PBz materials
from bio-based di-Bz monomers. Yet, the potential of PBz material from di-vanillin Bz monomer
was very limited because of its early thermal degradation (before melting) and its high melting
temperature. In the case of di-cardanol Bz monomer, the corresponding material is an easily
processable thermoplastic material that was poorly crosslinked and started creeping around 100
°C. In order to obtain an easily processable bio-based Bz monomer and with the aim to combine
178
the good thermal properties of vanillin-based Bzs and the low melting temperature of the
cardanol-based Bz monomer, we reported an efficient preparation of asymmetric bio-based di-
benzoxazines (named Vani-Card) via a two-steps synthesis pathway including a controlled mono-
substitution of cardanol-based benzoxazines followed by a coupling with vanillin. Such
combination resulted in a bio-based Bz monomer displaying a large processing window and high
thermal stability (Above polymerization temperature). The reactivity of this monomer was also
clearly enhanced in comparison to di-cardanol monomer as highlighted by rheology analyses. In-
depth characterization of the thermoset material resulting from asymmetric Vani-Card Bz
displayed very comparable thermal and mechanical properties to other known PBzs either
partially or fully based on renewable compounds. Finally the presence of the cardanol moiety was
shown to strongly improve the thermal stability of the PBz material as evidenced by TGA analysis.
This versatile approach is thus a powerful tool to access a wide range of asymmetric bio-based
benzoxazines given the large number of precursors available and their possible combination. It
paves the way toward easily processable high performance bio-based benzoxazines.
Finally, in the last chapter, we studied the macromolecular reinforcement of a diglycidyl ether of
cardanol (CDGE) based network. To this end, a poly(CDGE) network was combined through the
formation of interpenetrating polymer networks (IPNs) with a polybenzoxazine network
(poly(EDBz)). Since benzoxazine monomers are able to react not only with epoxies but also with
their diamine hardeners, an appropriate scrutiny of reactant systems and optimal curing
conditions was done. The elaboration of an poly(CDGE)/poly(EDBz) IPN structure was found to
be favoured by an in-situ sequential IPN synthesis. The first poly(CDGE) network can be
synthetized in a first curing step by polymerization of CDGE with isophorone diamine as hardener
at low temperature without interactions with the EDBz monomers present in the system. The
second poly(EDBz) network can then be synthetized by homopolymerization of the EDBz
monomers at higher temperatures. The properties of the poly(CDGE)/poly(EDBz) materials were
then studied in function of their compositions. As expected, DMA characterization highlighted an
increase of Tg and elastic moduli of the materials while increasing content of EDBz. The IPN
materials morphology was estimated by comparison to experimental models based on the
evolution of the storage moduli of the materials as a function of their composition. Our
experimental findings fit at very high accordance to the Davies model, tending to a co-continuous
system. Nevertheless, in spite of numerous attempts (atomic force microscopy, scanning electron
microscopy), it was not possible to observe these morphologies and up to now the viability of this
model is not confirmed. Finally, it was observed by swelling testing that the incorporation of
poly(EDBz) leads to a significant drop of the swelling of poly(CDGE) in water. In conclusion, the
179
feasibility of the concept of the elaboration of IPN from CDGE and EDBZ in order to reinforce the
poly(CDGE) network was achieved in this work.
In conclusion the various studies described in this manuscript highlighted the possibility of using
cardanol as a bio-based and very versatile building block for the elaboration of diverse materials
including bio-based thermoset materials (polybenzoxazines and epoxies), but also as a
component for the elaboration of composite materials. Indeed, in chapter II cardanol-based bio-
based surfactants were used to elaborate clay-epoxy nanocomposite materials. We could
conceive of applying this strategy for the reinforcement of bio-based polybenzoxazine materials
for example. Moreover, as described in the chapter III, we managed to elaborate a cardanol- and
vanillin-based polybenzoxazine material displaying good properties. In order to further enhance
those properties, we could elaborate bio-based polybenzoxazine-clay nanocomposite materials
using cardanol-based surfactants as clay organomodifiers. Nevertheless, the high performances
of PBz materials were strongly related to the formation of an H-bond network. In order to study
the interaction between pristine clay and PBz resins, prior to clay organomodification, we
proposed to study the supramolecular interactions between kaolin and poly(EDBz).149 The
thermal and thermo-mechanical properties of the benzoxazine resins were significantly
improved.
Finally, in chapter IV we described the improvement of the cardanol-based epoxy network
(poly(CDGE)) by the formation of IPN materials with poly(EDBz). Still, in order to improve the
properties of poly(CDGE), one can envision for example to tune the structural features of the bio-
based Bz varying the substituting groups. Indeed, the various functionalities on the bio-based
phenolic compounds would allow tailoring the PBz materials properties, as evidence by the effect
of the aldehyde function on vanillin for example. In consequence, it could be conceived to further
improve the poly(CDGE) material properties by various PBz resins bearing various functional
groups. To this aim, the strategy of synthetizing assymetric bio-based Bz monomers from
different bio-based phenolic compounds reported in chapter III could be considered.
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Annex: Materials and Methods
1 Chapter II: Surfactants from cardanol
1.1 Materials
Epoxy derivative of cardanol (commercial grade NC513) was kindly supplied by Cardolite.
Montmorillonite (commercial grade N116 – Cation Exchange Capacity CEC = 116 meq/100g) was
obtained from Southern Clay. Tris(2-aminoethyl)amine (TAEA) and N,N-
dimethylethylenediamine (DMEDA) were purchased from Acros and used as received without
any purification. Ethylene diamine (EDA), 1,2-diaminocyclohexane (DAC, mixture of isomers),
Bisphenol A diglycidyl ether (BADGE) and the solvents used for the synthesis of the surfactants
were all purchased from Aldrich and used as received without any purification.
1.2 Characterization methods
1.2.1 NMR analysis
The 1H nuclear magnetic resonance (NMR) characterization was performed on a Avance 400
spectrometer (Bruker Biospin, Wissembourg, France) equipped with a 9.4 T Ascend magnet,
operating at a proton frequency of 400 MHz. Samples were dissolved in CDCl3 with all peaks
referenced relative to tetramethylsilane.
1.2.2 Mass analysis
Matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS) experiments were
recorded using a Bruker Autoflex III mass spectrometer (Bruker Daltonics, Leipzig, Germany)
equipped with a frequency-trippled Nd-YAG laser (ƛ = 355 nm) operating at a pulse rate of 50 Hz.
For MALDI analyses, samples were submitted to a solvent-free preparation, consisting of grinding
the matrix together with the analyte with a mortar and a pestle. The matrix/analyte mass ratio
was optimized for each sample, around 1/10 appearing to be a quite universal ratio for the clay
mineral samples, while a 50/1 ratio being a routinely used for the organic analytes such as
cardanol-based surfactants. Trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-
propenylidene]malononitrile (DCTB) was used for the analysis of surfactants and clays (no salt,
to detect species protonated prior to the LASER irradiation), α-cyano 4-hydroxycinnamic acid
(CHCA) was only used for the surfactants (no salt, to promote the protonation of the amine
groups).
181
1.2.3 XRD analysis
Wide-angle X-ray scattering (WAXS) experiments were conducted by means of an X’Pert Pro MPD
diffractometer from PANalytical, with a copper Kα radiation (1.54 Å) generated at 45 kV and 40
mA in transmission mode. Scans were recorded from 1.5 ° to 30 °, step size 0.02 ° at 5 °/min
scanning rate.
1.2.4 SEM analyis
Scanning electron microscopy (SEM) analyses were performed using a QUANTA FEG 200 from
FEI in the low vacuum mode (with water vapor as chamber gas). Chemical contrast analyses were
performed with a Gaseous Analytical Detector (GDA) for low magnitude observations.
Topographic micrographs were recorded with a secondary electron detector (SE), the chemical
contrast micrographs with a backscattered electron detector (BSE) and local elemental analysis
performed by Energy dispersive X-ray spectroscopy (EDS). Samples were prepared by cryogenic
fracture.
1.2.5 DSC analysis
Differential scanning calorimetry (DSC) thermograms were recorded by means of a Netzsch DSC
204 F1 Phoenix apparatus operating at inert atmosphere (nitrogen) with a linear heating ramp
from 20 to 250 °C at 20 °C/min rate.
1.3 Surfactant synthesis
1.3.1 Synthesis and purification of CardS1
Typically 5 g (14 mmol) of NC-513 in 100 mL CHCl3 were added to 6 g (41 mmol) of TAEA in 10
mL CHCl3. The mixture was heated at reflux for 20 h; the consumption of NC-513 was followed by
TLC, indicating reaction completion.
The excess of amine was removed by one solvent extraction with NaOH in water (50 mg/L). The
organic phase was dried using K2CO3 and evaporated. Viscous orange oil was obtained.
1H NMR (CDCl3, 400 MHz, 298 K): δ (ppm) (s, assignment, experimental integration, theoretical
integration). δ = 0.91 (m, CH3 from alkyl chain, exp 1.8 H, th 1.7 H), 1.31 (m, -CH2 from alkyl chain,
exp 13.5 H, th 13.6 H), 1.59 (t, -CH2-Ar, exp 2.3 H, th 2 H), 2.04 (m, -CH2*=CH-, exp 3.4 H, th 3.1 H),
2.28-2.95 (m, -CH2- from amine moiety and =CH-CH2*-CH= from Cardanol, exp 15.6 H, th 16.1 H),
3.04 (s, -NH2, exp 4.3 H, th 4 H), 3.84-4.23 (m, H α oxygen atoms, exp 3.5 H, th 3 H), 4.93-5.90 (m,-
CH= from alkyl chain, exp 4.8 H, th 4.5 H), 6.68-7.21 (m, H-Ar, exp 4 H, th 4 H).
182
MALDI-MS. CHCA Matrix: Detected m/z, Elemental Composition, Assignment. m/z
501.42/503.43/505.45, C30H53/55/57N4O2+, [M (n=3/2/1) + H]+.
1.3.2 Synthesis and purification of CardS2
Synthesis of CardS2 is similar to the CardS1 synthesis. 10 g (28 mmol) NC-513 in 100 mL CHCl3
were added to 5 g (84 mmol) of EDA in 20 mL CHCl3. The excess amine was removed by two
solvent extractions in brine. The organic phase was dried over K2CO3 and evaporated. Viscous
yellow oil was obtained.
1H NMR (CDCl3, 400 MHz, 298 K): δ (ppm) (s, assignment, experimental integration, theoretical
integration). δ = 0.91 (m, CH3 from alkyl chain, exp 1.8 H, th 1.7 H), 1.32 (m, -CH2 from alkyl chain,
exp 13.0 H, th 13.6 H), 1.61 (t, -CH2-Ar, exp 2.2 H, th 2 H), 2.04 (m, -CH2*=CH-, exp 3.3 H, th 3.1 H),
2.47-2.93 (m, -CH2- from amine moiety and =CH-CH2*-CH= from Cardanol, exp 8.6 H, th 8.1 H),
3.18 (s, -NH2, exp 2.5 H, th 2H), 3.86-4.30 (m, H α oxygen atoms, exp 3.4 H, th 3 H), 4.90-5.93 (m,-
CH= from alkyl chain, exp 4.7 H, th 4.5 H), 6.64-7.25 (m, H-Ar, exp 4 H, th 4 H).
MALDI-MS. CHCA Matrix: Detected m/z, Elemental Composition, Assignment. m/z
443.36/445.38/447.39, C28H47/49/51N2O2+, [M (n=3/2/1) + H]+.
1.3.3 Synthesis and purification of CardS3
The synthesis of CardS3 was performed as the previous ones by adding 10 g (28 mmol) NC-513
in 100 mL CHCl3 to 7.40 g (84 mmol) of DMEDA in 20 mL CHCl3. After reaction completion the
solvent was evaporated, and crude CardS3 was dissolved in ethyl acetate. Two extractions in
brine were carried out, and the organic phase was dried with K2CO3, filtered and evaporated.
Viscous yellow oil was obtained.
1H NMR (CDCl3, 400 MHz, 298 K): δ (ppm) (s, assignment, experimental integration, theoretical
integration). δ = 0.91 (m, CH3 from alkyl chain, exp 1.8 H, th 1.7 H), 1.32 (m, -CH2 from alkyl chain,
exp 13.5 H, th 13.6 H), 1.61 (t, -CH2-Ar, exp 2.2 H, th 2 H), 2.04 (m, -CH2*=CH-, exp 3.6 H, th 3.1 H),
2.47-2.93 (m, -CH2- from amine moiety and =CH-CH2*-CH= from Cardanol, exp 13.6 H, th 14.1 H),
3.86-4.30 (m, H α oxygen atoms, exp 3.4 H, th 3 H), 4.90-5.93 (m,-CH= from alkyl chain, exp 4.9 H,
th 4.5 H), 6.64-7.25 (m, H-Ar, exp 4 H, th 4 H).
MALDI-MS. CHCA Matrix: Detected m/z, Elemental Composition, Assignment. m/z
415.33/417.35/419.36, C26H43/45/47N2O2+, [M (n=3/2/1) + H]+.
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1.4 MMT clay organomodification
Standard cation exchange procedures were employed for the preparation of organomodified
MMT (O-MMT).
Typical procedure it used to modify 1 g of clay consist in dissolving 1.12 g of CardS1 (2 equivalents
to MMT’s CEC) in 50 mL of EtOH at 80 °C. 20 mL of HCl solution in EtOH (0.1 M) were added to
protonate CardS1 to CardS1H+. The resulting solution was then added to the MMT/water
dispersion (100 mL water for 1 g of MMT) and the final mixture heated to 80 °C. The cation
exchange reaction was maintained for 16 hours at 80 °C under intensive magnetic stirring.
The O-MMT was filtrated and washed with 80 °C heated ethanol/water solution (50/50), until no
traces of Cl- could be detected with AgNO3. O-MMT are noted CardS1-MMT, CardS2-MMT and
CardS3-MMT.
1.5 Reaction of the intercalated surfactants with Fge
Furfuryl glycidyl ether (Fge) was used to evidence the residual reactivity of the surfactants
intercalated in O-MMT. Two drops of Fge were added to the dispersed O-MMT in CH2Cl2. The
mixtures were maintained under magnetic stirring for 8 hours at room temperature, and were
then filtered and dried at room temperature. The characterization of Fge-grafted surfactants was
done by MALDI- TOF/MS analysis.
1.6 Clay mineral-based polymer nanocomposite (CPN) preparation
10 mass% Clay/BADGE were prepared by mixing BADGE to O-MMT at 80 °C under vacuum during
1 hour. 1 epoxy-equivalent of DAC (1,2-diaminocyclohexane as the amine hardener) was then
added. The mixture was immediately transferred in a high-temperature silicone mold. The
thermal treatment was 2 h at 160 °C, followed by a post-cure at 190 °C during 2 h. The resulting
materials were characterized by X-ray diffraction and scanning electron microscopy.
2 Chapter III: Benzoxazines from cardanol
2.1 Materials
Cardanol (Ultralite 2023) was supplied by Cardolite. Ethylenediamine, paraformaldehyde,
vanillin, and the solvents were all purchased from Aldrich and used as received without any
purification.
184
2.2 Characterization methods
2.2.1 NMR analysis
1H NMR spectra were performed on a Brucker Avance 400 spectrometer equipped with a 9.4 T
Ascent magnet, operating at a proton frequency of 400 MHz. Monomers were dissolved in
deuterated chloroform with all peaks referenced relative to tetramethylsilane (TMS). In regard
to the integration of the NMR signals, the precise integration depends obviously on the
composition of cardanol and related proportion of different isomers. The integrations are usually
calculated by moderation based on the abundance of unsaturation described in the literature.11,
51, 204-206 These unsaturation abundances can slightly vary regarding the origin and the processing
of raw Cardanol extracted from CNSL. As such the integration may diverge from sample to other.
The unsaturations abundances of the used cardanol were considered as follow in our calculations:
tri-unsaturated (n=3) ~ 41%, di-unsaturated (n=2) ~ 23%, mono-saturated (n=1) ~ 34%,
saturated (n=0) ~ 3%. In addition, the difference of relaxation times between aromatic and
aliphatic hydrogen may complicate the accurate quantification of all protons. Therefore, the peaks
related to the aliphatic chain of cardanol were integrated to the aliphatic hydrogen in β position
of the cardanol aromatic ring, which should integrate for 2H whereas the peak from -OCH3
function on the vanillin compound that should integrate for 3H, was used as reference for all other
peaks including those related to the benzoxazine structure.
2.2.2 Mass analysis
Molecular characterizations were also performed by high-resolution mass spectrometry (HR-
MS), using a LTQ/Orbitrap Elite (Thermo Scientific) equipped with an atmospheric-pressure
matrix-assisted laser desorption/ionization source (AP-MALDI PDF+, Masstech). This analytical
setup allows for the investigation of MALDI-produced ions using accurate mass measurement
(sub-ppm relative error) and structural confirmation by MSn. Samples were submitted to a
solvent-free preparation. α-Cyano-4-hydroxycinnamic acid (CHCA) was used for the analysis of
the benzoxazine monomers, and used as received from Sigma-Aldrich (St Louis, MO).
2.2.3 DSC analysis
Differential scanning calorimetry (DSC) thermograms were recorded by means of a Netzsch DSC
204 F1 Phoenix apparatus operating at inert atmosphere (nitrogen) with a linear heating ramp
from 20 to 250 °C at 20 °C/min rate. Thermo-gravimetric analysis (TGA) was performed on a
Netzsch TG 409 PC Luxx device operating in synthetic air (nitrogen: 80 mL/min and oxygen: 20
mL/min) with heating ramp from ambient temperature to 250 °C.
185
2.2.4 Rheology analysis
Rheo-kinetic measurements were performed with an Anton Paar Physica MCR 301 rheometer
equipped with a CDT 450 temperature control device with plate-plate (diameter 25 mm, measure
gap 0.5 mm) geometry. The polymerization measurements were recorded in oscillation mode at
an imposed 1 % deformation at 1 Hz frequency at 190 °C.
2.2.5 DMA analysis
Dynamic mechanical analyses (DMA) were carried out on bar samples (5x10x0.5 mm3) with a
Q800 model (TA instruments) operating in tension mode (strain between 0.05 and 0.07 %;
pretension, 10-2 N) at 1 Hz with a heating rate of 3 °C/min from ambient temperature to 250 °C.
2.2.6 TGA analysis
Thermo-gravimetric analysis (TGA) was performed on a Netzsch TG 409 PC Luxx device
operating in synthetic air (nitrogen: 80 mL/min and oxygen: 20 mL/min) with heating ramp from
ambient temperature to 250 °C.
2.3 Synthesis of the Bz monomers
2.3.1 Synthesis of the di-cardanol Bz monomer
Cardanol (5.96 g, 20 mmol, 2 eq) was reacted with EDA (0.60 g, 10 mmol, 1 eq), and
paraformaldehyde (1.27 g, 40 mmol, 4 eq) in CHCl3 at 70 °C for 48 h. The crude reaction was
washed three times with 1 M NaOH solution to remove unreacted phenolics and/or formed
oligomers, and the chloroform phase was neutralized by three washings with distilled water. The
solvent was removed under vacuum and the product was purified over column chromatography
(Heptane/Ethyl acetate = 7/3) to yield a white wax.
1H NMR (CDCl3, 400 MHz, 298 K) δ = 0.86-0.94 (-CH3 from cardanol alkyl chain, exp 4.08 H, th 3.54
H), 1.23-1.43 (-CH2 from cardanol alkyl chain, exp 27.59 H, th 27.12 H) 1.54-1.64 (-CH2 β from Ar,
aliphatic proton reference 4.00 H) 1.98-2.09 (CH2*=CH, exp 7.47 H, th 6.20 H) 2.49-2.57 (CH2—
Ar, exp 4.47 H, th 4.00 H) 2.76-2.87 (CH2*(=CH)2), exp 4.74 H, th 4.20 H) 2.99 (N-CH2*-CH2,
benzoxazine structure reference th 4.00 H) 4.03 (Ar-CH2-N, exp 3.98 H, th 4.00 H), 4.89 (O-CH2-N,
exp 4.00 H, th 4.00 H) 4.96-5.88 (CH=, exp 1.69, 7.55, 0.94 H, th 1.64, 6.48, 0.82 H) 6.60-6.90 (H-
Ar, exp 2.01, 2.07, 1.93 H th 2.00, 2.00, 2.00 H).
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2.3.2 Synthesis of the di-vanillin Bz monomer
Vanillin (3.04 g, 20 mmol, 2 eq) was reacted with EDA (0.60 g, 10 mmol, 1 eq) and
paraformaldehyde (1.27 g, 40 mmol, 4 eq) in CHCl3 for 24 h. The product was purified over
column chromatography (Heptane/Ethyl acetate = 7/3) to yield a white powder.
1H NMR (CDCl3, 400 MHz, 298 K) δ = 3.02 (N-CH2*-CH2, exp 3.70 H, th 4.00 H) 3.95 (O-CH3,
benzoxazine structure reference 6.00 H) 4.13 (Ar-CH2-N, exp 4.01 H, th 4.00 H), 5.08 (O-CH2-N,
exp 4.02 H, th 4.00 H) 7.13-7.32 (H-Ar, exp 1.99, 1.99 H, th 2.00, 2.00 H) 9.81 ((C=O)H, exp 2.00
H, th 2.00 H).
2.3.3 Synthesis of the di-phenol Bz monomer
Phenol (1.88 g, 20 mmol, 2 eq) was reacted with EDA (0.60 g, 10 mmol, 1 eq), and
paraformaldehyde (1.27 g, 40 mmol, 4 eq) in CHCl3 at 70 °C for 24 h. The crude reaction was
washed three times with 1 M NaOH solution to remove unreacted phenolics and/or formed
oligomers, and the chloroform phase was neutralized by three washings with distilled water. The
crude reaction mixture was then washed with 1M NaOH solution and dried to obtain a white
powder.
1H NMR (CDCl3, 400 MHz, 298 K) δ = 3.02 (N-CH2*-CH2, exp 4.08 H, th 4.00 H) 4.07 (Ar-CH2-N, exp
4.02 H, th 4.00 H), 4.92 (O-CH2-N, exp 3.73 H, th 4.00 H) 7.78-7.15 (H-Ar, Ref 8.00 H, th 8.00 H)
9.81 ((C=O)H, exp 2.00 H, th 2.00 H).
2.3.4 Synthesis of the Vani-Card asymmetric Bz monomer
First reaction step: cardanol (5.98 g, 20 mmol, 1 eq) was reacted with EDA (1.20 g, 20 mmol, 1
eq) and paraformaldehyde (1.27 g, 40 mmol, 2 eq) in CHCl3 for 24 h. Second reaction step: vanillin
(3.04 g, 20 mmol, 1 eq) and paraformaldehyde (1.27 g, 40 mmol, 2 eq) were added to the reaction
crude and the reaction was continued for 24 h. The product was purified as described for di-
vanillin to yield a light orange wax.
1H NMR (CDCl3, 400 MHz, 298 K) δ = 0.85-0.96 (-CH3 from Cardanol alkyl chain, exp 2.04 H, th
1.77 H), 1.23-1.41 (-CH2 from cardanol alkyl chain, exp 13.53 H, th 13.56 H), 1.54-1.64 (-CH2 β
from Ar, aliphatic protons reference 2.00 H), 1.98-2.09 (CH2*=CH, exp 3.41 H, th 3.10 H), 2.49-
2,56 (CH2-Ar, exp 2.00 H, th 2.00 H), 2.75-2.87 (CH2*(=CH)2, exp 2.36 H, th 2.10 H), 2.95-3.09 (N-
CH2*-CH2, exp 3.99 H, th 4.00 H), 3.86-3.94 (O-CH3, benzoxazine structure reference 3.00 H), 4.01
(Ar-CH2-N from cardanol, exp 1.99 H, th 2.00 H), 4.13 (Ar-CH2-N from vanillin, exp 1.99 H, th 2.00
H), 4.88 (O-CH2-N from cardanol, exp 1.98 H, th 2.00 H), 4.96-5.88 (CH=, exp 1.00, 3.76, 0.46 H th
0.82, 3.24, 0.41 H) 5.08 (O-CH2-N from vanillin, exp 1.99 H, th 2.00 H), 6.60-6.88 (H-Ar from
187
cardanol, exp 1.07, 1.06, 1.00 H, th 1.00, 1.00, 1.00 H), 7.12-7.34 (H-Ar from vanillin, exp 1.00,
1.01 H, th 1.00, 1.00 H), 9.81 ((C=O)H, exp 1.01 H, th 1.00 H).
2.4 Material elaboration
Monomers (di-cardanol or Vani-Card) were degased during 1 h above melting temperature (50
and 105 °C, respectively) and then transferred to a U-shaped mold. A curing program of 1 h at
160 °C was applied followed by 2 h at 180 °C and the samples were post-cured for 2 h at 200 °C
and 30 min at 220 °C.
3 Chapter IV: Interpenetrating Polymers Networks (IPN) from cardanol-based thermoset
networks
3.1 Materials
CDGE (Commercial name NC-514) was supplied by Cardolite (EEW = 490 g/eq). 1,2-
diaminocyclohexane (mixture of isomers) was purchased from Sigma-Aldrich and used as
received. The EDBz benzoxazine monomer was synthetized and purified as described in the
Chapter III.
3.2 Characterization methods
3.2.1 DSC analysis
Differential scanning calorimetry (DSC) thermograms were recorded by means of a Netzsch DSC
204 F1 Phoenix apparatus operating at inert atmosphere (nitrogen) with a linear heating ramp
from 20 to 250 °C at 20 °C/min rate for the analyses of the curing of the monomers.
The evolutions of the melting enthalpies of water were recorded on the swollen samples with the
following heating program at inert atmosphere (nitrogen): cooling from ambient temperature to
-50 °C at a rate of 20 °C/min, 5 min isotherm at -50 °C followed by a heating to 40 °C at a 5 °C/min
heating rate.
3.2.2 Solvent extraction
The solvents extractions of the materials at various curing steps were achieved by CHCl3
extractions in a Soxhlet for 72 h. After extraction the samples were dried under vacuum and then
weighed and characterized by DSC analysis.
188
3.2.3 DMA analysis
Dynamic mechanical analyses (DMA) were carried out on bar samples (5x10x0.5 mm3) with a
Q800 model (TA instruments) operating in tension mode with strain at 0.05 %; pretension, 10-2
N) at 1 Hz with a heating rate of 3 °C/min from ambient temperature to 250 °C.
3.3 Material elaboration
The reference materials from EDBz and CDGE, as well as the IPN materials with various
compositions, were elaborated by first mixing the CDGE pre-polymer and the EDBz compound at
100 °C and degasing during 1 h at 100 °C, followed by the addition of the IPD hardener in
stoichiometric ratio to the CDGE monomer (The stoichiometric amount of hardener was
determined by calculation with the equivalent epoxy weight EEW). The mixtures were then
transferred to a U-shaped mold. The previously determined curing program of 16 h at 100 °C, 1 h
at 160 °C, 2 h at 180 °C, 2 h at 200 °C and 30 min at 220 °C was applied to each material.
189
Annex: Figures
Figure 1. 1H NMR spectrum (in CDCl3) of cardanol.
Figure 2. Isothermal rheology monitoring of di-cardanol Bz monomer at 190 °C.
190
Figure 3. Isothermal rheology monitoring of Vani-Card Bz monomer at 190 °C.
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