cours composite [1]

8/8/2019 Cours Composite [1]

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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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