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Polymer (nano)composites
: key-role of chemistry
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Composite :
Natural composites Natural comp
osites
Bone structure
Fibrillar
collagen
Hydroxyapatitecrystals
(500nm x 250nm x 25 nm)
Mother-of-pearl Nacre
Silk proteins
Heterogeneous association of two or several non-miscible materials, generally of different chemical nature, forming a multi-phase material characterized by a set of
properties that none of the individual constituent displays separately.
Spider thread
Crystals of alanine-rich proteins
Glycin-richamorphous
matrix (70%)
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Wood structure :
Chemical composition
Typical hard wood anatomy
Constituent Weight fraction(%)
Cellulose 45-50Hemicelluloses 20-35
Lignin 22-30
Extractives 0-10
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Woodstructure :
Macrofibril
Microfibri
l
Cellulose chains
Cellulose
fibers
Lignin matrix
Natural fiber composite Crystalline cellulose Matrix of hemicellulose,
lignin, and amorphouscellulose
High stiffness especiallyin fiber direction
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Synthetic composites Syn
thetic composites
- Used for thousands of years like Pis (adobe : blend of mud and straw)
-More recent : concrete (cement and gravel)
- Modern composite matrials :
- Polymers filled with particles (end of 19th century)
- Polymers reinforced by continuous fibers (since ~1935)
DefinitionsDefinitions ::
- Matrix : continuous phase, embedding the dispersed materials. When thematrix content is much less than the dispersed phase, the matrix can be named
binder .- The dispersed phase is often called reinforcement since its main roleaims to enhance the matrix resistance to mechanical constraints.
- These reinforcement materials are usually formed of continuous fibers (unidirectionial, woven or non-woven mat) or particles (isotropic or anisotropic).
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Types of matrices :
- metallic, ceramic, polymeric;
Types de fibers :
- metallic (rares), ceramic, carbon-based, glass, polymeric (Kevlar,Dyneema);
Types of reinforcing particles :
- silica, alumina, clays (kaolin, mica,), metals, carbon black, graphite,
Various families :
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Typical example : polyethylene filled with reinforcing Typical example : polyethylene filled with reinforcing inorganic particlesinorganic particles
Hydrophobic Hydrophilic-surfacepolyethylene Particulate fillers
Fillers aggregation =>mechanical brittleness
Uniaxial
constraint
Generation of voids => propagationof the rupture
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Uniaxial
constraint
Generation of voids => propagation
of the rupture
(From Prof. G. Marosi)
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Materials Stiffness Brittleness(fast
deformation)
Brittleness(slow
deformation)Youngsmodulus
Impactstrength
(IZOD test)
Elongation atbreak
(tensile test)(GPa) (J/m) (%)
HDPE0.7 80 900.0
HDPE + 40wt% kaolin 3.1 17 1.6
HDPE + 40wt% mica 6.5 20 0.3
HDPE + 40wt% CaSO4 2.8 15 1.3
HDPE + 40wt% CaCO 3 2.7 21 3.0
Effect of particulate fillers on mechanical properties
BRITTLENESS non-homogeneous mineral dispersion
poor mineral-polymer interaction
* High density polyethylene (Mw ~
*
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Tensile testing machine Impact testing machine
ISOD
CHARPY
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Solutions ?1) Decrease the hydrophilicity of the filler surface
Chemical treatment of the filler surface(alkoxysilane, alkylamine, Al carboxylates,)
Improvement of thedispersion Poor adhesion
Less brittle composite materials
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2) (Polymer) grafting reaction onto filler surface
via chemical treatment of filler surface with coupling agents
(vinylic or methacrylic alkoxysilanes, aluminum methacrylates,) followed by polymer grafting all along melt blending/processing
Improved dispersion Reinforced adhesion =>Mechanical rupture within the
matrix !
igidity and resistance to break significantly improved
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Filler - Polymer Dispersion / Interaction
Surface modification of thefiller
Surface agents (monofunctional) :
-silanes;-alkylamines;-Al carboxylates;-titanate esters; ...
Coupling agents* (difunctional/radical
grafting): -vinyl silanes;-aluminum
methacrylates; ...
Better filler dispersion with at best some improvement of adhesion*
Filler pre-encapsulation Surface coating by a crosslinked resin layer (Ceraplast
technology)(as diffuse ca.12nm interface of intermediate elastic
modulus)-coupling agent ( -unsaturated amines)
-difunctional monomers (dienes,dimethacrylates)
-thermally activated initiators (peroxydes)
Combination of stiffness/toughness - costly
Polymerization from the fillersurface
POLYMERIZATION-FILLED COMPOSITES : PFCs
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Polymerization-Filling Technique
Filler
Z.-N. Catalyst
Filled-Polyolefin
Olefin
(i.e., ethylene)
fixation of a Ziegler-Natta type catalystonto the filler
olefin polymerization from the fillersurface/pores
ENIKOLOPIAN N.S., USSR Pat. 763,379 (1976)HOWARD E.G., US Pat. 4,104,243 and 4,097,447 (19
PFT on a wide range of fillers :
acidic surface (kaolin, silica,glass beads,)
basic surface (magnesiumhydroxide,...)
organic fillers (graphite, carbonblack,...)
metallic fillers (nickel, zinc,)
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Polymerization-Filling Technique
y developed for Ziegler-Natta catalysts (transition metal complexes
Transition metal ( M)
Sublimation,Impregnation or
Deposition
Solid ( M) phase on thefiller surface
Support-OH + MRn
Support-O MRn-1 + RH
Physicaladsorption
Chemicalgrafting
Catalyst types : Ti : TiCl 4 /AlR 3 ; Ti(BH 4)3 ; Ti(OR) 4 /AlR 2Cl
Zr : Zr(CH 2-C 6H5)4 ; Zr(BH 4)4
V : VCl 4 /AlR 3 ; (VCl 3 + VO(OEt) 3)/AlEt 2Cl
Cr : CrRCl 4 ; Cr(O 2CR) 3
Hf : Hf(CH 2-C 6H5)4 ; Hf(BH 4)4
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tallocenes : Single Site Catalysts in Olefin Polymerization
eneral structure activation by methylaluminoxane MAO
MXX
+ A l O
CH3
Al O
CH3
X n
MCH3
+
M = Ti, Zr, Hf X = Cl, CH3, ...
n
MAO for : - methylation- cationization
- protic scavenger action
Properties
-High catalyst activity-Molecular weight control
(sensitivity to hydrogen)-Copolymerization with -olefins
(thermoplastic to elastomer)mol% comonomer
molecular masses
Ziegler-Natta
metallocene
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PFT via Metallocene Catalysts
filler
MAO
Composite
Metallocene Monomer
Deagglomeration
of the filler
Fixationpossible on
basic, acidic,organic,metallicsurfaces
Protection of
activecatalyst
Immobilization of the active species
throughelectrostaticinteractions
Homogeneousdispersion of the fille
MtR
(+)Al O
CH3
X n
(- )
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T via metallocene catalysis : some applications
iller precoating : Dispersion of coated glass beads in HDPE
Precoating of glass beads byeither polyethylene (HDPE) or ethylene/1-octene copolymer (LLDPE)
and composites filled with 20 wt% glass beads
Composite
HDPEMatrix
Filler coating(wt %)
E (Gpa) r (%) r (MPa) I.E. (kJ/m2)
1a) - 1.7 636 24.7 12.0
1a)
HDPE (14.5) 1.3 659 28.5 150.510 b) - 1.4 4.2 26.4 14.5
10 b) LLDPE (7.0) 1.5 6.9 28.9 41.0
a) Melt flow index under 2.16 kg load MI2 = 1 g/10min.; b) MI2 = 10 g/10min.
bare glass beads/HDPEcomposite
coated glass beads/HDPEcomposite
AFM Phase detection
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