polymner clay nanocomposite

Polymer Clay Nanocomposite


Bhupendra Singh

Department of Chemical Technology

University of Mumbai

Matunga, Mumbai – 400 019

Introduction Nanocomposites have changed the perception towards the concept of polymer composite.

They are the emerging polymer composites of the 21st century. The importance of these

products is growing from industrial and research point of view. Nanocomposite show

drastic improvement in the properties derived from the addition of few percent of the

clays in the polymer matrix. These composites exhibit new and improved properties as

compared to their micro and macro-composite counterparts. This improvement in the

properties is the result of the ultra fine phase dimension of the filler. A nanocomposite is

defined as “a material having two phases, one of the phases is uniformly dispersed into

the second phase on nanoscale level (10-9 m)”. The dimension of the first phase is in the

nanometer range of 1 to 100 nm.1 Nanocomposites typically contain 1-5 wt. % of filler

loading on weight basis depending on the final properties to be achieved.2

Nanocomposite promise to be the wave of future by having major implications in

industry and technology.3

The purpose of this paper is to present an overview on polymer clay nanocomposite, their

synthesis, properties, characterization and application.

By – Bhupendra Singh


Raw Materials

Polymer

Polymer clay composites have been classified into three categories namely, conventional

composite, intercalated nanocomposite and exfoliated nanocomposite depending on the

type of dispersion. In conventional composites the filler loading is on the higher side (30-

60 vol. %)1 as compared to the nanocomposites (1-5 wt. %). In intercalated

nanocomposites regular insertion of the polymer in between the silicate layers at the

molecular level is observed while in exfoliated nanocomposites individual layers of the

silicate layers are randomly dispersed into the polymer phase.3, 4

Different polymers have been used for the synthesis of the polymer clay nanocomposites

in the last decade. These polymers are divided into two different classes3

Thermoplastics

Thermosets

Thermoplastics

The first polymer clay nanocomposite synthesis was reported by Toyota Central R & D a

dozen year ago. Researchers have gone a long way since then in this arena and had

developed various nanocomposites by making use of different polymer and clay

combinations. Out of various thermoplastics used; polyamide-6 is the most studied and

reported nanocomposite. Injection molded polyamide-6 nanocomposite showed excellent

mechanical, barrier, heat distortion property and reduced flammability;5,6 without

sacrificing its impact strength4.Various polyamide-6 nanocomposite products have been

already commercialized.

Thermoplastics such as Poly (ε-Caprolactam ),1,7,8 PET,9 PMMA,10 PP,11,12 PE,12 PS,13

PES,14 PEO,15 Polyimide16 have been used for the synthesis of polymer clay



nanocomposite. Different methods are employed to synthesize these nanocomposites

such as Melt intercalation process, In-Situ polymerization and Solution process.

Processing of these nanocomposites can be done by conventional methods i.e. Injection

and Extrusion processes.

Thermosets

The most commonly studied thermoset nanocomposites are Epoxy,3,17 Polyurethane9,18

and unsaturated polyesters. Epoxies are the most widely used engineering thermoset

materials as it is easy to process and gives excellent engineering properties on curing.3

For thermoset nanocomposites the complete exfoliation of clay is predicted by

thermodynamic principle. The free energy, ΔG for complete exfoliation of thermoset

nanocomposite is the sum of the terms contributed by the polymer matrix and silicate

clay.

For polymer matrix

ΔGp = ΔHp - TΔSp

For silicate clay

ΔGc = ΔHc – TΔSc

The total free energy change is

ΔGt = (ΔHp + ΔHc) - T (ΔSp + ΔSc) = ΔHt – TΔSt

When monomers or polymers penetrate into the silicate layers the entropy change is

negative while expansion of the gallery shows positive entropy change. The total

enthalpy will determine whether or not exfoliation takes place.



The complete exfoliation condition is that the heat of the intergallery polymerization

released before the gel point requires larger than the van-der Walls attractive energy

between the interlayer. i.e., ΔHp (t ≤ tg) ≥ ΔHc .17

Clay

Clays have been used as fillers in the conventional polymer composites at very high

loading levels for economic reason. The property enhancement is moderate, which is in

contrast with the property improvement in the nanocomposite; where small amount of

filler loading gives higher level of property improvement.1 Clay is a generic name for a

whole family of layered aluminosilicates. Clays are used in wide variety of applications

like ceramic, decorating and industrial products depending upon its form and properties.

Smectite are the fraction of Bentonite ores. Smectite shows its unique property of

swelling in water. There are many species of smectite, of which Montmorillonite and

Hectorite19are of commercial importance. The most commonly used clays in

nanocomposite are organically modified Montmorillonite. Along with montmorillonite

few other types of clay have been reported for the use in the nanocomposite, such as

Saponite,20 Attapulgite 21 and Mica type 16, 19 silicates.

Montmorillonite

Approximate formula for montmorillonite is

[R+0.33(Al, Mg)2Si4O10(OH)2.nH20 ]

Where R+ in natural mineral can be one or more of the Na+,K+,Ca+2,cations.22

Montmorillonite have a dimension below the visible light wavelength; properly oriented

and transparent, this is a critical requirement in barrier packaging. Na-montmorillonite is

the major mineral constituent of Bentonites and has high swelling capacity as compared

to Bentonites having Ca–montmorillonite as major mineral. Na-montmorillonite is a

smectite in which Na and water molecules are the interlayer material. The largest and



highest quality Na – Bentonite deposits in the world are situated in South Dakota,

Wyoming and Montana. 23

Montmorillonite are the preferred materials in nanocomposite because of

Low levels of loading

High aspect ratio ( as high as 1000 )

Good transparency

Safe handling

Natural abundance

Economic and

Good chemical resistance 1,7

Montmorillonite shows hydrophilic nature; hence it can not be homogeneously dispersed

into the organic polymeric phase. The higher aspect ratio of silicate particles can be

maximized by dispersing individual silicate layers into the polymer matrix.1 Therefore to

incorporate montmorillonite into the polymer phase it is organically modified by a cation

exchange reaction.7 This improves the compatibility of montmorillonite with the polymer.

Owing to its cation exchange properties the clay gallery ions can be replaced by organic

cationic species such as alkyl ammonium ions. As the gallery cation changes from

inorganic to organic, the surface property changes from hydrophilic to organophilic.3

Compatibilizing Agents

Clays do not disperse well in the organic polymer matrix. The differences in the surface

tension force between the clay and polymer matrix; produces an obstacle in the

dispersion of clay particles in the polymer. The direct blending results in clustering

tendency of the silicate layers, thus posing limitation on its use as nanoclays. Hence

chemical modification is essential for the clay before using it in nanocomposite.9The

inorganic cations present in the clay intergallery provide the site for the water molecules

to form monolayer or multilayer structure. The layered spacing is governed by the

amount of water present. This makes clay hydrophilic in nature. To mix the clay with the

polymer matrix its hydrophilicity has to be decreased and organophilicity has to be



improved. As smectite clays exhibit cation exchange properties, the clay gallery ions can

be replaced by organic cationic species, such as alkyl ammonium ions. 3 Compatibilizing

agents are typically a molecule having one hydrophilic and one organophilic functional

group. Non polar nature of the alkyl chain reduces the electro static interactions between

the silicate layers to facilitate the diffusion of the polymer into the galleries of layered

silicate.

Organically modified montmorillonite is synthesized by a cation exchange reaction

between montmorillonite and alkyl ammonium ion or amino acids. The presence of this

cation in the galleries provides hydrophobicity to the Na- montmorillonite.4 Na -

montmorillonite has composition of sodium ion and negatively charged montmorillonite.

It forms homogeneous dispersion in water but does not disperse in the organic polymer

matrix. To reduce the hydrophilicity and improve the organophilic nature of Na-

montmorillonite it has to be treated with compatibilizing agent.16 Various compatibilizing

agents have been used for the synthesis of the polymer clay nanocomposite.

Compatibilizing agents such as 11-amino acid,24 octadecylammonium salt,4 12-

aminolauric acid,2,19 dimethyl dehydrogenated tallow quaternary ammonium chloride,5

have been employed for the nylon-6 clay nanocomposite synthesis.

Disteryldimethlyammonium chloride,7 cetyltrimethyl ammonium bromide (CTMA),25

dimethylpropanediamine 26 12-aminododecanoic acid1 were used in the preparation of

poly(ε-caprolactone) clay nanocomposite.

Dimethyl dehydrogenated tallow quaternary ammonium chloride is reported to be used in

the synthesis of SAN-MMT nanocomposite by solution polymerization method.10

Ammonium salt of dodecylamine was incorporated as compatibilizing agent for the

synthesis of polyimide nanocomposite.16 n-Hexadecylammonium chromide17 and alkyl

ammonium chloride3 was used in the Epoxy/clay nanocomposite as compatibilizing

agent.



Nanocomposite Synthesis

Nanocomposites can be synthesized by different routes. Most commonly used routes are

Melt-intercalation process

In-situ polymerization process

Solution process

Emulsion polymerization

Melt intercalation process (Compounding process)

This method involves mechanically blending organically modified clays with polymer

matrix. The nanocomposite is formed by addition of swollen and pretreated layered

silicate to the polymer melt. The swollen clay permits easy exfoliation of clay in the

polymer matrix.27 The nanocomposite is then annealed.28 Annealing of the polymer clay

nanocomposite sample at the extrusion temperature leads to coarsening of the clay

(silicate) superstructure and further improvement of exfoliation. This resulted in unique

rheological properties and stable morphology.29 The quality of dispersion depends on

1. Organic modifier

2. Processing and

3. Mixing conditions5

This is a promising new approach to fabricate polymer clay nanocomposite by using

conventional polymer processes like extrusion and injection molding. The formation of

nanocomposites by above processes is governed by the thermodynamic interaction

between the polymer chains and the silicate layers; and the transport of the polymer

chains from the bulk melt into the silicate layers.4 The polymer and nanofillers are

preconditioned to remove moisture. The polymer is then fed into the compounder along

with nanoclay with calibrated volumetric feeders.



The layered silicates are dispersed in the melt phase by shearing action. High shearing

mixers or internal mixers are used for the synthesis of the nanocomposite. Twin screw

compounder is ideal equipment. Screw parameters and compounding parameters are

modified to achieve the optimum properties. Nylon-66 films are casted by using high

shearing single screw or twin screw compounder. A schematic representation of the flow

diagram for melt-intercalation process is as shown below in fig. 1

Fig. (1) Flow chart for the synthesis of nanocomposite by melt-intercalation process

The particle size of the layered silicates in the nylon 6 matrix is reduced through the melt

intercalation process. Most of the silicate layers are exfoliated into nanometer layers and

randomly dispersed in the nylon 6 matrixes via melt intercalation process.4 TEM results

showed that the intercalated silicate layers through the melt extrusion process are

exfoliated into nanoscale layers and randomly dispersed in the nylon-6 matrixes.

In situ polymerization process (In reactor polymerization)

In-situ polymerization method is very useful method for the preparation of high

performance polymer nanocomposites.17 In this method nanocomposite is synthesized by

introducing the monomer, into the organically modified clay and then polymerizing it in-

situ. Kojima Etal.30 has reported the preparation of Nylon-6 nanocomposite at normal

pressure. In his experiments montmorillonite was dispersed in water, to which ε-

carolactam and hydrochloric acid was added. It was then stirred and filtered to get

montmorillonite intercalated with ε-carolactam. This intercalated ε-carolactam is then

charged into a reaction vessel along with 6-Aminocaproic acid. The mixture was heated


Clay

Thermoplastic

Blending Annealing Nanocomposite


at 2600C for 6 hours in nitrogen atmosphere under normal pressure. After reaction

completion the product was cooled and subjected to milling operation to obtain pellets.

Kurachi and co-workers at Toyota R&D have reported following procedure for the

synthesis of nanocomposite. A 2 L Parr reactor is charged with ε-carolactam and

montmorillonite that had been reacted with 12- aminolauric acid. The vessel was then

purged with nitrogen for 25 minutes and sealed. The temperature is raised to 1100C and

again purged with nitrogen for 30 seconds. Temperature is then raised to 2500C under

nitrogen atmosphere. The reaction proceeds for two days with slow stirring. Pour the

molten polymer into cold water, filter it and dry it for 24 hours at 0.1 mm Hg pressure.2 In

most cases the synthesis involves either intercalation of a suitable monomer and then

exfoliating the layered host by subsequent polymerization.4

Flow diagram for In-Situ Polymerization process is as shown fig. (2)

Fig. (2) Flow diagram for In- Situ polymerization process

Swelling of clay

Silicate layers swell in the monomer and exfoliate during the polymerization. Swelling

occurs because of monomers entering into the gallery between the silicate layers; which

increase the intergallery height. As the silicate layers move apart from each other the

mutual attraction between them decreases resulting in the drop of shear rate required to

disperse the silicate layers into monomers. The two important factors affecting swelling is

swell time and temperature during swelling.


Clay

Swelling

Monomer

Polymerization Nanocomposite


Dispersion Procedure

Dry silicate layers are added to the monomer under stirring condition. The stirring should

be enough to create a homogeneous mixture. Temperature is increased to ease the

monomer intrusion into the gallery between the silicate layers. Further stirring is

continued and the mixture is then charged into the reactor. The polymerization of the

mixture is carried out under agitation and blanket of nitrogen. After the completion of the

reaction the nanocomposite is washed, palletized and dried. This dried nanocomposite is

then used for making the final product.31

Viscosity Control

Viscosity of the mixture tends to increase while mixing. To control the viscosity water

can be added to the mixture without affecting the dispersibility of the clay. Also as

silicate clay and polymer mixtures are thixotropic in nature hence viscosity can be

controlled just by increasing the shear rate. The ε-caprolactam containing nanoclays have

a tendency to develop increased viscosity while polymerizing.

In-situ formed polymer clay nanocomposite outperformed melt compounding by a

significant margin. The resulted nanocomposite has a “tethered” system where polymer

molecules terminate at the clay surface. Tethered systems show enhanced thermal

stability with improved fire retardancy property.31

Solution polymerization

Organically modified clay is suspended in suitable solvent under vigorous stirring

condition. Organoclay swells in the solvent. To this mixture monomer and initiator is

added. The mixture is allowed to react while vigorous stirring condition is maintained.

Reaction is then terminated. The product is separated and washed several times. It is then

dried under reduced pressure to remove the washing solvent.

Preparation of SAN- MMT nanocomposite is reported by using this method.10 A

modified method is used to prepare Rubber-Clay nanocomposite. In this method instead



of monomer as used above; polymer dissolved in solvent is added to the mixture of

preswollen organoclay. The last step consists of removing the solvent by evaporation

under vacuum.32 Figure (3) represents the steps involved in the solution polymerization

process.

Fig. (3) Flow diagram representing the steps involved in the solution polymerization

process.

Emulsion Polymerization

A new approach to the polymer nanocomposite synthesis; based upon one step emulsion

polymerization is reported by M. H. Noh Etal. Various properties such as polymer

loading into the inter layer of silicates, molecular masses of intercalated polymer, gallery

expansion, thermal stability, mechanical properties and dispersibility of silicate layers in

polymer matrix was found to exceed to those of products made by solution

polymerization method. Emulsion polymerization can play an important role in synthesis

of polymer clay nanocomposite; it also eliminates the environmental problems associated

with the solution polymerization process.

It involves addition of surfactant along with unmodified silicate clay under stirring

condition. Monomer is feed with the initiator. Emulsion polymerization proceeds under

vigorous agitation condition. The reaction mixture is cooled to room temperature. The

final product is obtained after filtration and washing several times with water. It is then


Clay

Monomer

Swelling

Solvent

Intercalation & Polymerization

SolventEvaporation

Nanocomposite


dried under reduced pressure. Styrene-Acrylonitryl copolymer montmorillonite

nanocomposite is prepared by the Emulsion Polymerization technique.10 A flow diagram

for emulsion polymerization technique is as shown in the figure (4)

Fig. (4) Flow diagram for the synthesis of nanocomposite by emulsion polymerization

process

Characterization

For the characterization of the polymer clay nanocomposite X-Ray Diffraction (XRD),

Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM),

Differential Scanning Calorimeter (DSC) and NMR were used. Studies of structural and

morphological characteristic were carried out.

TEM images of N-6/clay nanocomposite showed that the silicate layers disperse

uniformly in the polymer matrix. The microstructure in the nanocomposite was found

similar to that of organoclay, but the interlayer distance was observed to become larger to

3.5 nm; which is compatible with XRD results.4

DSC studies showed the presence of clay promoted γ-crystalline form. From DSC scan

curve it was observed that the Nylon-6 matrix has only one peak corresponding to the α-


Clay

Monomer

Polymerization

Water

Surfactant

Nanocomposite

Initiator


form while the nanocomposite system shows two melting peaks; high temperature peak

corresponding to α-form and the lower temperature corresponding to γ-form of

crystallite4.

NMR studies were carried out for the observation of α and γ crystal forms and amorphous

regions in Nylon-6 clay nanocomposites.

Crystallization behavior of Nylon-6 nanocomposite

Nylon-6 is a multicrystalline polymer having more stable α–form as compared to γ-form.4

Clays induce the γ- crystal growth in nylon 6 while the percentage crystallinity remains

almost the same.2 Generally α-phase and amorphous phase is observed in nylon-6; of

these α- phase is the favored one. Annealing of nylon samples at a temperature close to

the glass transition temperature produces only α and amorphous phases. While, when clay

particles are present in nylon-6, it adopts α and γ-crystal phases in somewhat equal

amounts. Since only α form is present in commercial nylons hence it can be suggested

that the presence of γ- phase must be a result of the interactions between the silicate

layers and the polymer matrix. Clay increases the crystallization rate and has a strong

nucleation effect on the nylon 6 matrix.4 The clay stabilizes or /and induces the γ- phase

of nylon-6 in nanocomposite. The results of crystallization study after annealing for

nylon-6 and nylon-6 nanocomposite showed no change in crystalline and amorphous

phase for nylon-6 but at the same time the morphology was changed for the

nanocomposite as it produced only γ-form of crystal and amorphous phase. The clay

surface induces kinetically favored formation of γ-crystal form.2 It is well established that

the presence of clay induces the formation of γ-form of crystal as compared to α form of

crystal.5

Small amount of clay in nanocomposite promotes the crystallization while large clay

content delays it. The isothermal crystallization is affected by diffusion and nucleation.

Diffusion is related to the activation free energy for transporting polymer segment to the

growing crystal surface. Nucleation term is related to the thermodynamic driving force. A



small amount of clay acts as a nucleating agent while large amount hinders the

transportation of polymer segment.7

Orientation

The nanocomposites exhibit anisotropic properties which are attributed to the orientation

of the clay layers. The preferential orientation of the clay layer in the polymer clay

nanocomposite was found to be related to the injection / extrusion direction. This

orientation of the clay layer plays a major role in the enhancement of the mechanical

properties of the polymer clay nanocomposite.33

Orientation of montmorillonite and nylon-6 crystallites in nylon composite film is

measured by X. R. D. and TEM. For the film it is seen that the pure nylon-6 film showed

no preferred orientation but on the other hand presence of silicate layers contributes

important role in the preferred orientation of nylon-6 crystallites. γ-form of nylon 6

crystallites tends to form planar orientation in the nylon clay nanocomposite film.6

In nylon clay nanocomposite film it was found that the silicate layers had planar

orientation. The chain axes of nylon-6 crystallites (γ- form) were found parallel to the

film surface but were randomly oriented within the film plane. This orientation of nylon-

6 crystallites in nanocomposite was assumed to be promoted by the presence of

anisotropic silicate monolayer dispersed separately. The degree of orientation of an

anisotropic body depends on both the magnitude of the applied shear stress and the aspect

ratio of the body.34.

Properties

Properties of the nanocomposite material is governed to a greater extent by complex

interactions between different phase and the interfaces between them.3


d d’

L

W


Mechanical properties

Surface modified silicates used in extrusion melt compounding when properly mixed

with melt enhances the mechanical properties. For Nylon-6 clay nanocomposite the

flexural modulus increases rapidly with increasing clay content from 0-3.5 wt %. Further

increase in the clay content has little effect on the flexural modulus. Flexural strength

approaches to peak at 3 wt % and decreases with further increase of the clay content. The

tensile modulus increases in the range 0-15 wt % but little effect was observed for clay

content higher than 15 wt %.Notch impact strength remains almost constant in the range

0-17 wt %. For low filler content the properties were found to be far superior to those of

conventional counterpart composites. There is a strong interaction between the matrix

and the clay layers which attributes to the nanoscale size and uniform dispersion of the

clay layers in the nylon-6 matrix. 4,30

Barrier Properties

The barrier properties of the polymer clay nanocomposite were enhanced by the addition

of nanoclays in the polymer matrix. A conceptual figure for the path of a diffusing gas

through the polymer nanocomposite is as given in the figure (5)

Fig (5) Mechanism

of “tortuous path”



Total path of a diffusing gas

d’ = d + d.L.Vf / 2W

d - thickness of a film

L - length of clay

W- width of clay

If silicate layers are dispersed parallel in the polymer matrix the torturous factor (τ) is

given by

τ = d’ / d

τ = 1 + (L / 2W) Vf

Vf- volume fraction of clay

Therefore relative permeability coefficient is given by

Pc / Pp = 1 / [1 + ( L / 2W ) Vf ]

This equation roughly estimates the mechanism of “tortuous path” in polymer

nanocomposite.16

Sorption properties of nylon 6 clay nanocomposite

Nylon-6 has inferior resistance to water permeation. Hence it is of great importance to

improve the resistance of Nylon-6 to water permeation since rigidity of the polymer is

lowered by water absorption. Nylon-6 nanocomposites exhibit excellent resistance to

water permeation because of the decrease in the diffusion coefficient as compared to

Nylon-6. The diffusion coefficient decreases with increase in the length and content of

the silicate layers.20 Water vapor transmission of nanocomposite film is determined by

ASTM E 96.1



Thermal properties

The HDT increases rapidly for nylon-6 nanocomposite with an increase in the clay

content from 0-5 wt. %. Nanocomposites offer effective flame retardancy without

affecting the environmental problems.4 Nylon-6/clay nanocomposite prepared by

intercalation compounding shows that peak value of heat releasing rate of the

nanocomposite decreased by 32% and 63% when the clay content was 2% and 5%

respectively. The density of the nanocomposite was found to be 65-75% of that of general

composite.35

Ablative property

A relative tough, inorganic char formed during the ablation of the nylon-6

nanocomposite. An order of magnitude decrease in the mass loss rate was observed as

compared to the pure nylon. This property was observed for as little as 2 wt% exfoliated

mica type silicates. The uniform distribution of the silicate layers at nanoscale leads to the

formation of uniform char layer resulting in enhanced ablative property. The formation of

char depends on specific interaction between the polymer and the clay surface.36

Mechanism of Intercalation and Exfoliation

Intercalation

Regular insertion of polymer in between the silicate layers is observed in intercalated

nanocomposites. The polymer to layered silicate ratio is almost fixed. They show

electronic and charge transportation properties. Intercalation of 2 vol. % silicate into

Nylon-6 on a nanoscale improved the tensile strength and modulus by more than twice as

compared to the pristine polymer.3



Exfoliation

In exfoliated nanocomposite the number of polymer chains between the layered silicates

(clay) is variable. These nanocomposites show superior mechanical properties. In

exfoliated nanocomposite 1 nm thick layers are dispersed forming a monolithic structure

at the micro scale. The ability of the silicate layers to exfoliate is affected by factors such

as ion exchange capacity of the silicate, the polarity of the matrix, and the chemical

nature of the interlayer cations. Matching the polarity of the organic cation with the

monomer is very critical for getting good dispersion.1

As the polymer layer enters into the silicate layers, the interlayer spacing of the clay

increases and the interaction between the clay layer decreases. If the miscibility of the

polymer is good enough then it achieves the exfoliated homogeneous dispersion of the

clay.37 Figure 6 represents the mechanism of intercalation and exfoliation.


10Ao

2000Ao

Exfoliation

Silicate layer

Intercalation

CompatibilizerPolymer chain


Figure (6) Diagram representing the Intercalation and Exfoliation in polymer clay

nanocomposite



Individual Nanocomposite

Polyamide

Nylons are widely used as plastic materials for specialty purposes. They can be injection

and extrusion molded. Nylons are used in automobiles, electrical goods, packaging

applications; because these materials exhibit good mechanical, thermal and barrier

properties.38 Semi-crystalline polymers crystallize in different phases (e.g. Monoclinic,

Hexagonal) forming chain folded lamellar crystals. The stability of these phases depends

on experimental conditions (e.g. temperature, pressure) and crystal size. The

nanocomposites prepared by In-Situ polymerization and Melt intercalation method

exhibited homogeneous distribution of the silicate layers into the polymer matrix at low

clay contents. These composites show enhanced thermal stability, tensile modulus and an

increased elastic behavior over a broad temperature range. No effect on Tg was observed

at highest clay content.39 TEM studies for Nylon -6/clay nanocomposite showed the clays

to be 1 nm thick, 100 nm wide layered filler.40

Meta-xylene adipamide (MXD6), a specialty aliphatic nylon. Intercalated

nanocomposites of MXD6 with modified phyllosilicate silicate (smectite clay) layer

showed expansion in the intergallery spacing by at least 5Aº.

Poly (ε-caprolactone)

Poly (ε- caprolactone) is biodegradable aliphatic polyesters and their use in degradable

packaging, medical devices and controlled drug release systems is under investigations.

For poly (ε-caprolactone) - silicate nanocomposite the permeability was reduced by an

order of magnitude at only 4.8 % loading by volume. Full delamination of the

nanocomposite leads to the formation of high aspect ratio (100-1000) impermeable layer

having very good barrier property.1



Polymethylmethacrylate (PMMA)

PMMA is polymerized in presence of sodium lauryl sulfate with potassium persulfate in

the presence of Na- Montmorillonite at 70oC for 12 h. It is then coagulated by adding

aluminum sulfate solution. The product is then filtered and dried to form the

nanocomposite.

The average interlayer distance of the composite was found to be higher than the pristine

polymer. TGA thermogram of the weight loss as a function of temperature showed the

shift in the thermal decomposition temperature towards the higher temperature range as

compared to the pure PMMA.

The tensile modulus of the composite was found to be increased with the increase in the

clay content. The improvement in the tensile modulus is due to the higher resistance

exerted by the clay layer against the plastic deformation and the effect of the oriented

backbone bonds of polymer chain in the gallery.

In DSC studies the nanocomposite does not show any clear transition as compared to the

pure PMMA, which shows endotherm at approximately at 102oC, corresponding to the

Tg of the PMMA.41

Polyimide

Polyimides are used in microelectronics as it has good heat resistance, chemical stability

and superior electric properties. For its use in advanced electronics it is desirable to

reduce coefficient of thermal expansion, moisture absorption and dielectric constant.

Layers of organically modified montmorillonite are dispersed homogeneously into the

polymer matrix. These layers align themselves parallel to the surface. A film of polyimide

nanocomposite containing 2 wt. % of montmorillonite is found to be as transparent as

polyimide itself. This phenomenon occurs because of molecular level dispersion and the

size of montmorillonite (< 200 nm ) being lesser then the wavelength of visible light. As



the content of montmorillonite increases in the polyimide nanocomposite the thermal

expansion coefficient decreases notably. This will play an important role in matching the

thermal expansion coefficient of nanocomposite to that of silicon substrates in electronic

applications.16

PET nanocomposite

PET is a polymer having low cost and high performance, finds variety of applications in

packaging films, bottle and engineering plastic applications to fiber application. In PET

nanocomposite the exfoliated silicate layers acts as nucleation promoter. With a clay

content of 5%, the modulus of nanocomposite was improved as much as 3 times that of

pristine PET. The average particle size distribution ranges from 10-100 nm. The heat of

fusion decreases with the content of clay; and the HDT increase with the content of clay.

The melting point of the PET nanocomposite decreased slightly with the content of clay.

At the degradation temperature of the nanocomposite, the nanoscale particle showed

strong interaction with the polymer matrix; thus explaining the enhancement in the

degradation temperature.9

PP/clay nanocomposite

PP containing organophilic layered silicate nanocomposite was prepared by melt

extrusion process at 210º C. PP-g-MA used as a compatibilizer, led to strong exfoliation

of silicate layers within the polymer matrix. Annealing of the sample at the processing

temperature led to coarsening of the silicate superstructure and improvement in the

exfoliation. Stable morphology with network like superstructure was obtained by this

process.29

In another process montmorillonite dispersed in water and ethylene glycol was treated

with hexadecyl trimethyl ammonium bromide. The dried dispersion was mixed with PP

melt using an extruder, from which the glycol was evaporated.27

A house of cards structure in PP/clay nanocomposite under elongational flow was

observed in TEM analysis.42



PP-g-MA Nanocomposite

PP-g-MA/Layered silicate nanocomposite was prepared by melt intercalation process

using PP modified with maleic anhydride by solid- phase grafting process.

Montmorillonite was modified with octadecylammonium ion. This nanocomposite

showed higher tensile strength and modulus as compared to PP and PP-g-MA. Dramatic

improvement in the tensile property was observed up to the silicate content of 3% and

remained constant over 5%. The nanocomposite showed the faster crystallization than

PP-g-Ma.43

PES nanocomposite

Low molecular weight reactive fume silica was successfully dispersed to nanoscale in

PES matrix with small amount of low molecular weight epoxy. Viscosity and processing

temperature were reduced significantly. Improvement in the barrier property and heat

deflection temperature was observed over pristine PES.14

PS nanocomposite

A shear induced ordered structure was observed in an exfoliated PS/clay nanocomposite.

A series of sharp XRD peaks was reported for the extruded PS/clay nanocomposite as

compared to the broad peaks of PS. The ordered structure resulted from the planer

orientation and local ordered microstructure of the 1º particles of silicate layers, induced

by shear flow.13

ABS nanocomposite

The mixture of acrylonitrile and butadiene- styrene was subjected to polymerization in

the presence of fluoromica as clay. The fluoromica was ion exchanged with

benzalkonium ion and 4- vinylpyridinium ion. The mixture was then suspension

polymerized in aqueous poly (vinyl alcohol) to form a precursor. This precursor was then



blended with ABS copolymer and butadiene rubber in a twin screw extruder to form the

nanocomposite.44

PEO

PEO-block-PS copolymer was prepared by melt-intercalation technique. Samples having

higher PEO volume fraction were more likely to produce intercalation.28

Epoxy/clay nanocomposite

The organic modified clay is easily intercalated by the epoxy precursor during the

mixing process. Addition of suitable catalyst and coupling agent into the cured system

significantly reduces the maximum reaction temperature thus leads to favorable reaction

in the formation of Epoxy nanocomposite.17

Applications

Nanocomposites have been rapidly commercialized for different applications.

Nylon-6 and PP nanocomposites are used for packaging and injection molded articles.

Semi-crystalline nylon nanocomposites have been used for barrier, containers and fuel

tank system applications. Layered silicate promotes rapid crystallization; hence better

clarity is obtained as compared to pristine nylons; which makes them ideal for film

applications. Nanocomposites can be run at higher line speeds as a result of improved

strength. MXD6 nanocomposite is finding its use as a barrier resin in packaging

applications. It is very useful in applications requiring good barrier properties in high

humid conditions. Nylon clay nanocomposite having excellent mechanical and heat

resistance property find its use in automobile parts. Nylon nanocomposite film having

good barrier property finds use in wrapping films for food industry.45

Polyamide nanocomposite prepared by melt intercalation process can be used in all

molded parts which can be produced using polyamide compounds. It find use in the

motor compartment of a vehicle for casing and for connectors.46 Polymer clay



nanocomposites are widely used in electronics, transportation, construction and consumer

products as they exhibit combination of properties like stiffness and toughness which are

not present in individual polymers.4

Polyimides find use in microelectronics because of it superior electric properties.16

Alicyclic copolymer mixed with disteryl dimethylammonium chloride treated

montmorillonite was found to be useful for automobile parts, electrical parts and

packaging applications.47 Polyamide sheets containing 4 % montmorillonite showed

reduced curling and were useful for packaging drug tablets.48 Multilayer fuel tanks with

excellent gasoline barrier properties and fire resistance were manufactured by HDPE/

clay nanocomposite.49

A subclass of nanocomposite by using graphite as nanofiller may be used as conducting

polymer.50

Conclusion

Nanocomposites can be synthesized for both thermoplastic as well as for thermoset.

Conventional processes such as injection and extrusion molding are employed to get the

final product. The drastic enhancement in the nanocomposite properties is attributed to

the ultra fine phase dimensions of the filler and homogeneous dispersion in the polymer

matrix. To get homogeneous dispersion the compatibility of the clay with polymer matrix

has to be improved. The type of clay and chemical treatment governs the dispersion of

the clay. Compatibilizing agent plays an important role in the dispersion. Low levels of

loading, high aspect ratio, cation exchange capability and natural abundance makes the

Montmorillonite the most effective clay for use in the nanocomposite. Various

compositions of polymer and clay nanocomposite have been developed by different

processes. Manipulation in the compositions will result in getting optimum properties.

The enhanced mechanical properties, barrier properties will increase its use in the

automotive and packaging industry.



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