dispersion nucleating--effects of polymer nanocopmposites

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AMRUTHA K S 2 ND M.Sc BPS CBPST, KOCHI

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Page 1: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

AMRUTHA K S

2ND M.Sc BPS

CBPST, KOCHI

Page 2: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

Introduction While large surface-to-volume ratio of nanoparticles makes

them superior reinforcements over conventional fillers, it

also brings difficulties in dispersing the nanoparticles due to

their strong interactions among themselves. Due to these

inter nanoparticle interactions, it is extremely difficult to

disperse nanoparticles uniformly, specially at higher particle

loadings.

Several processing methods including shear mixing,

mechanical mixing, in-situ polymerization and sonication

have been used for dispersing nanoparticles in polymers.

Page 3: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

Effect of Dispersion at High Particle Loadings

In shear mixing and sonication to disperse montmorillonite

clay nanoparticle into vinyl ester resin. The clay nanoparticle

loading was 3-8% by weight. The compressive results of

clay modified resin showed that the resin with 5% nanoclay

exhibited a reasonable improvement in compressive strength

and a considerable (20%) improvement in modulus.

However the mechanical properties, especially strength,

tended to go down when nanoclay was loaded beyond 5

wt%.

Page 4: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

16% improvement in tensile strength and 90% improvement in tensile modulus were reported at 5wt% loading of fillers

3wt% 5wt% 8wt%

Page 5: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

Epoxy matrix modified with modified with silica nanoparticles

(up to 14 vol%) via sol-gel method enhanced the mechanical

properties of polymer nanocomposites such as modulus,

microhardness, and fracture toughness. It is therefore

reasonable to say that the sol-gel method can be used to produce

well dispersed high nanoparticle loading nanocomposites with

much improved mechanical properties.

Page 6: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

Dispersion of Particles of Different Sizes

While particle dispersion plays the foremost role inenhancing polymer’s properties.

it is also greatly influenced by the size of particles. Smallerparticles have higher surface area (at same particle volumefraction) and,

Hence, greater surface interactions among the particles. Thisis what makes the dispersion of nanoparticles harder.

Nanocomposites show increase in modulus with thedecrease in particle size that leads to dispersion moredifficult.

Page 7: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES
Page 8: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

Nucleation

In polymer technology, especially for injection molding the

desired high crystallization rates often require the addition of

nucleating agents.

A nucleating agent is substance that forms nuclei for the growth

of crystals in super cooled polymer melt. virtually ay solid body

with a high energy surface may act as a nucleating agent closely

matches the crystallization surface of polymer.

The nucleating agent may preferably induce a crystallographic

form of the polymer. for e.g., addition to isotactic PP of either

1,2,34-bis(3,4-dimethyl-benzylidene sorbitol) or N,N’-

dicyclohexyl-2,6-naphthalate dicarboxamide, preferably generate

a-iPP or b-iPP, respectively

Page 9: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

The nucleating efficiency depends on several independent

variables, such as temperature,pressure,stress,part thickness

as well as the presence of the other processing additives

An efficient nucleating agent must have a high-energy

surface-the large the specific surface ,the more efficient it is

expected to be.

Nucleation involves initial adsorption of macromolecules on

the surface. the process is particularly efficient if the foreign

body is able to provide a energetic matrix for the formation

of thermodynamically favorable crystalline forms.

Page 10: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

Alternatively, the crystalline cell type ad size of the nucleating

agent may induce a transitory crystalline polymer forms that

upon annealing transforms into a stable form of higher packing

density

The nucleating efficiency may be expressed in terms of the

energy ratio required to generate a nucleus in a heterogeneous

nucleation over that in a homogenous one.

The nucleation is the rate determine step, while the extend of

crystallinity is constant. Thus the nucleation rate ,r , depends on

the degree of super cooling ,

Page 11: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

Where,

Em is the energy required to form a nucleus ,

is a geological factor ,

is the specific surface energy ,

Vm is the molar volume of the crystalline substance.

is the melting entropy,

n is the Avrami exponent and

kb is the Boltzmann constant.

Page 12: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES

Nanofillers such as clay may have high

nucleating effect. The wide variety of

intercallatants,intercalating methods and

compatibilisers may form a barrier between

high energy clay surface and semicrystaline

polymer matrix.

Page 13: DISPERSION  NUCLEATING--EFFECTS OF POLYMER NANOCOPMPOSITES