Toward High Value Thermoplastic Lignin Polymers
H. Sadeghifar, C. Cui,
S. Sen Dimitris S. Argyropoulos*
Departments of Chemistry and Forest Biomaterials North Carolina State University , Raleigh , NC USA
& *Advanced Materials Research Center of Excellence,
King Abdulaziz University, Jeddah, Saudi Arabia.
Lignin is the second most abundant biopolymer on the planet
Together with cellulose they can be considered as the batteries of the planet
Lignin structure is highly irregular but extremely challenging
Lignin presents opportunities for our chemical industry since it represents the reduced part of the lignocellulosic substrate compared to sugars
Objective
To describe our philosophy and approach aimed at creating heat stable technical lignin melts
& Aimed at Thermoplastics, Precursor to carbon Fibers & Engineering Heat Stable Polymers
Fundamental Science aimed at Creating Thermoplastic Lignin Melts
Heat Stable Polyarylene Ether Sulfone -Kraft Lignin Co-Polymers
Defining the Science & a Novel Approach aimed at Creating Carbon Fibers from Lignin Melts
Fundamental Science aimed at Creating Thermoplastic Lignin Melts
Softwood kraft lignin is highly susceptible to thermally induced
reactions that cause its molecular characteristics to be severely
altered. These events seriously interfere and prevent such materials
from being considered as candidates for thermoplastic applications.
MeO
OH
CHCH
CH
MeO
OH
SCH2OH
COOH
CHCH2OH
HC
OHOMe
OH
O O
HOOC
OMeO
O
MeO
CHOHCHCH2OH
HO
MeO
OH
OH
CH
CH
OHOMe
C
CH2
O
CH CH
OMe
O
CHC OCH2
OH
CH2
HOH2C
OHOMe
CHCHO
CH2OH
CH2
MeO
OH
OMe
COOH
Kraft Lignin Structure
Marton, J. 1971.
Effect of Heating on the Molecular Weight Distribution
of Underivatized Kraft Lignin
Cui, C., et al. “Toward Thermoplastic Lignin Polymers; Part II: " BioResources 8(1), 864-886, (2013).
Starting Softwood Kraft Lignin “Indulin” Molecular Weight : Mw = 8000 (g/mol) Mn = 2000 ( g/mol) ( Mw/Mn = 4 ) Total phenolic-OH = 3.85 mmol/ g Total Aliphatic-OH = 2.4 mmol/g Tg : 150-160°C .
MeO
OH
CHCH
CH
MeO
OH
SCH2OH
COOH
CHCH2OH
HC
OHOMe
OH
O O
HOOC
OMeO
O
MeO
CHOHCHCH2OH
HO
MeO
OH
OH
CH
CH
OHOMe
C
CH2
O
CH CH
OMe
O
CHC OCH2
OH
CH2
HOH2C
OHOMe
CHCHO
CH2OH
CH2
MeO
OH
OMe
COOH
Effect of Heating Between 120-140 °C on MWD of Underivatized Kraft Lignin
Annealing Temperature, °C --- 120 130 140
Mw (g/mol) 8000 13000 128000 340000
Mn ( g/mol) 2000 2030 2200 2100
Mw/Mn 4 6.4 58.2 162 H. Sadeghifar , Toward Thermoplastic Lignin Polymer Part I , Ind. Eng. Chem. Res., 2012, 51 (51), pp 16713–16720 DOI: 10.1021/ie301848j
OOCH3
R
OOCH3
OOCH3
OOCH3
H�
�
�
OOCH3
�H
OOCH3
OOCH3O
H3CO�H
OOCH3OH
H3CO
Rearomatization
Radical Coupling
4-O-5 Ether Linkage Formation
OOCH3HO OCH3
OH3CO
H
H
Rearomatization
OHOCH3
OHH3CO
Radical Coupling
5-5' Linkage Formation
Kawamoto, et al. J. Wood Sci. 2007, 53(2) &53(3)&27(2); J. Anal. Appl. Pyrolysis 2008, 81 (1), 88-94. Holzforschung 2008, 62 (1), 50. Ohashi, et al.. Org. Biomol.. Chem. 2011, 9 (7), 2481-2491
O
O
H
L
OOCH3
OCH3
O
L
OHOCH3
OCH3
-HCOH
Quinone Methide
O
O
H
L
OOCH3
OCH3
Formaldehyde Generation
O
OH
L
OOCH3
OCH3
Quinone Methide
O
OH
L
OOCH3
OCH3
�
�
Phenoxy Radicals
Kawamoto,et al, J. Wood Chem. Technol. 2007, 27 (2), 113-120.; Holzforschung 2008, 62 (1), 50
Working Hypothesis & Statement of Purpose
• Since the phenolic OH is implicated as being pivotal in
thermal events operating within lignin we aim to devise
technically feasible methods to selectively protect
these groups in kraft lignin and examine their effects
on their thermal properties
• Methylation with Methyl Iodide in ( DMF ) • Methylation with Dimethyl Sulfate in NaOH
Lignin Methylation
A L
OH
L
OMeOMe OMe
CH3I , DMF, K2CO3
(CH3)2SO3, NaOH(aq)
H. Sadeghifar , Toward Thermoplastic Lignin Polymer Part I , Ind. Eng. Chem. Res., 2012, 51 (51), pp 16713–16720 DOI: 10.1021/ie301848j
Comparison of Methylation Effectiveness as a Function of Reagent Concentration
Phenolic-OH Methylation with Dimethyl Sulfate is a lot more effective & Selective than Methyl Iodide.
0 0.25 0.5 1 1.5 2 2.5
3.85
3.1
2.31
1.73
1.24
0.5
0.03
3.66 3.52
2.9
2.4
1.8 1.6
mmol/g
Lignin
Molar ratio of methylation reagent/phenolic-OH
Methylation with dimethyl sulfate Methylation with methyl iodide
Kraft lignin methylation with (CH3)2SO4
Ratio of (CH3)2SO4 to total phenolic-OH in lignin
The progressive and selective elimination of phenolic-OH’s is apparent CONFIDENTIAL
Kraft Lignin Oxypropylation with Propylene Oxide in Aqueous Base
H. Sadeghifar , Toward Thermoplastic Lignin Polymer Part I , Ind. Eng. Chem. Res., 2012, 51 (51), pp 16713–16720 DOI: 10.1021/ie301848j
Kraft Lignin Oxypropylation
• Procedure • Kraft lignin was reacted with propylene oxide in 0.5M NaOH solution
at 40°C for 12hrs with stirring • Degree of oxypropylation was measured by phosphorus NMR
L
OH
L
O-CH2CH-O-CH2CHO-HOMe OMe
NaOH (aq)O
CH3 CH3 n
H. Sadeghifar , Toward Thermoplastic Lignin Polymer Part I , Ind. Eng. Chem. Res., 2012, 51 (51), pp 16713–16720 DOI: 10.1021/ie301848j
How does the Phenolic OH & its Derivatives Define the Thermal
Reactivity of Kraft Lignin ?
Effect of Heating Kraft Lignin & Derivatives 20 0C above Tg on Molecular Weight
Cui, C., et al. “Toward Thermoplastic Lignin Polymers; Part II: " BioResources 8(1), 864-886, (2013).
Effect of Heating on the Molecular Weight Distribution
of Fully Oxypropylated Kraft Lignin
Cui, C., et al. “Toward Thermoplastic Lignin Polymers; Part II: " BioResources 8(1), 864-886, (2013).
Effect of Heating at 150 °C on Fully Oxypropylated Kraft Lignin Molecular Weight Distribution as a Function of Time
Heating Time ( min) 0 1 5 20 40 60
Mw , g/mol 9000 44000 58000 150000 210000 210000
H
OO
HH
H
HL
OR
HO
H
L H+
LH
HH
OH HO
OxoniumIon
Deprotected Phenolic OH
Hydride Transfer
- H2O
H2O
Why Oxypropylated Lignin Shows Thermal Lability ?
•Facile dehydration of 20 OH of the oxypropyl substituent •Dehydration facilitated by an immediate α-hydride transfer forming an oxonium intermediate •New phenolic OH group generated from the deprotection
Olah G.& Prakash, G. K. S., Carbocation Chemistry. J. Wiley & Sons,.: New Jersey, 2004. Vollhardt, K. P. C.& Schore, N. E., Organic Chemistry: Structure & Function. NY. 2007.
Since methylation of the Phenolic OH with Dimethyl Sulfate showed promising thermal stability…
• Is this stability permanent ? • Can the material withstand heating &
Cooling cycles ? • How does the Molecular Weight
Distribution of the material is affected by repeated Heated & Cooling Cycles? Polymer Processing Simulating Conditions.
2nd Heating
3rd Heating
Minute Changes in the Mol. Wt Distributions are Indicative of the Sought Chemically Stable Melt Characteristics
Cui, C., et al. “Toward Thermoplastic Lignin Polymers; Part II: " BioResources 8(1), 864-886, (2013).
MeO
OH
CHCH
MeOOH
SCH2OH
COOH
CHCH2OH
HC
OH
OH
O O
HOOC
OMeO
O
MeO
CHOHCHCH2OH
HO
MeO
OHOH
CHCH OH
OMe
CH2C
O
CHCH
OMe
O
CHC OCH2
OH
CH2
HOH2C
OHOMe
CHCH
OCH2OH
CH2
MeO
OH
OMe
COOH
OH
OHOMeMeO
OOMe
OHHO
OH
OH
(B)
MeO
(A)
(A)
(A)
(A)
HO
HO
OH
OH
HO
HO
A+A
4-O-5
Ether
Linka ge
Form
ation
A +A
5 -5 Li nk ag e
F ormati on
A+BA-A, B-B and
A-B Linkag es
Formation
HO
HO
OH
OH
A multitude of inter & intra molecular thermal events in Kraft lignin may be avoided by the selective and complete methylation of its phenolic OH groups. Thus preventing the phenoxy radicals & QM’s from forming and reacting .
Toward Carbon Fibers from Technical Lignin
Defining the Science & a Novel Approach aimed at Creating Carbon Fibers from Lignin Melts
S. Sen, et al. “Toward Thermoplastic Lignin Polymers; Part III: " Biomacromolecules (2013).
Since derivatization of the Phenolic OH allowed the modulation of the thermal stability…
Eventual aim: Carbon Fibers from Lignin
• Can one modulate thermal crosslinking? • Can one regulate the rate of Mol.
Weight Increase? • By introducing activated (thermally
labile) centers how does the Molecular Weight Distribution of the material is affected ?
KL 20% methylated 80% activated 150 °C, 10 min
KL 20% methylated
80% activated 150 °C, 60 min
KL 20% methylated 80% activated 150 °C, 10 min
KL 20% methylated 80% activated 170 °C, 10 min
KL 20% methylated
80% activated 150 °C, 60 min
KL 20% methylated 80% activated 150 °C, 10 min
The molecular weight distribution gradually increases with increasing temperature and time of heating
Toward Heat Stable Poly (Arylene Ether)
Sulfone-Lignin Heat Stable Copolymers
Why Poly (Arylene Ether Sulfones) • Ease of preparation, • Ease of functionalization, • Thermal & chemical stability • Relatively low cost • Excellent mechanical performance.
Copolymerization of Kraft Lignin with DifluoroDiphenyl Sulfone (DFDPS)
SF FO
O
Ar OHL DMSO/toluene-H2O
Ar O-Na+L
Ar O-L
SF
FO
OOAr L
-SF
FO
OOArL
-
SF
FO
OAr L
O-
SF
FO
OOAr L
-
S FO
OOArL
-X-
Ar OHL = Lignin molecule with phenolic -OH end group
NaOH
0
0.2
0.4
0.6
0.8
1
1.E+001.E+011.E+021.E+031.E+041.E+051.E+06
22% Methylated KL-DFDPS Co-Polymer
Starting Kraft Lignin
71% Methylated KL-DFDPS C0-Polymer
63% Methylated KL-DFDPS C0-Polymer
38% Methylated KL-DFDPS Co-Polymer
Size Exclusion Chromatographic Analyses of Methylated Kraft Lignin DFDPS Co-Polymers .
Typical Step growth polymerization Mol wt. distribution shapes are observed, progressively moving to higher molecular weights
13C NMR Spectra of Starting Kraft Lignin & Its Co Polymer with DFDPS
Initial Kraft Lignin
Copolymer of Kraft Lignin with DFDPS
13C NMR Spectra of Starting Kraft Lignin & Its Co Polymer with DFDPS
13C NMR Spectra of Starting Kraft Lignin & Its Co Polymer with DFDPS
13C NMR Spectra of Starting Kraft Lignin & Its Co Polymer with DFDPS
13C NMR Spectra of Starting Kraft Lignin & Its Co Polymer with DFDPS
Thermal Degradation Analyses of Methylated Kraft Lignin DFDPS Co-Polymers
DFDPS
71% Methylated KL-DFDPS Co-Polymer
38% Methylated KL-DFDPS Co-Polymer
35.0
45.0
55.0
65.0
75.0
85.0
95.0
100 150 200 250 300 350 400 450 500 550
KL-DFDPS Co-Polymer
Kraft lignin
Heat stabilities up to 270 0C are observed for these Kraft Lignin DFDPS Copolymers with Tg values at least 100 0C lower
Differential Thermal Scans of Methylated Kraft Lignin DFDPS Co-Polymers .
Tg,172 °C
Tg,170 °C
Tg,166 °C Tg,147 °C
Glass Transitions Temperature (Tg) as Function of Molecular Weight for a Series of Kraft Lignin –DFDPS Co-Polymers
90
147
166 170
60
80
100
120
140
160
180
1200 3900 5900 6800
Tg ,
°C
Molecular Weight , g/mol
100 % Lignin
74 % Lignin
69 % Lignin
86% Lignin
Conclusions
• The selective methylation of the phenolic OH is pivotal in
controlling the thermal stability of technical Lignin
• Molecular Weight Distribution measurements offer a
detailed way of understanding such thermal events
• 100% Kraft Lignin Thermoplastic Polymers & Specialty
Copolymers are possible
Conclusions
• Thermoplastic Co-polymers of Polyarylene ether Sulfones
with Kraft Lignin have been synthesized displaying :
- Typical Step Growth Mol. Weight Distributions
- Excellent Thermal Stability
- Predictable Mol. vs Wt. Tg Relations
Strategic Decisions
• Treating Lignin with respect will pay off • Focus & capitalize on current limitations • Expand into Hardwood & Biorefinery
Lignins • Work with Specific Lignin for specific
high value applications • Work with Industry to bring these to
further development
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