Chapter II

Literature Review

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

A new class of materials based on organic and inorganic species combined at

nanoscale level has gained ever more attention during the last decade. These new

materials called nanoscale materials ordered nanocomposite; organic or inorganic

hybrids can be considered as the composite in which at least one phase is of below

100-nm size. The polymer –clay nanocomposites first reported in the literature by

Blumstin et al [1], author illustrated system with polymerization of vinyl monomers

intercalated into montmorillonite.

Nanocomposites are commonly based on the polymer matrices reinforced by modified

nanofillers such as precipitated silica, silica alumina, silica beads, cellulose whiskers,

zeolites, natural and synthetic modified silicates (Insitu method)[2-4]. Clays are

intensively used in nanocomposites. The layered silicates (natural clay) like mica,

laponite, fluorohectorite can be synthesized. Most of the recent studies have focused on

the use of natural clay from smectite family “Montmorilonite” because of its layer charge

density [5-7]. It is most widely used nanofiller. Montmorillonite contains in the addition

varying amount of crystobalite, zeolites, quartz, felspar, Al2O3 identically found suitable

in high cutting tools, high surface area support catalyst, tribological materials, heat sinks

and magnetic recording heads [8].

Ph.D.Thesis, Mr. Shriram Shaligram Sonawane, U.D.C.T. N.M.U., Jalgaon Page 21

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2.2 Synthetic Routes for Nanoparticles and Nano Composites

2.2.1 Synthesis of inorganic nano particles

There are number of techniques currently available for the synthesis of nanoparticles of

oxides and non oxides, these include laser ablation[9], microwave plasma synthesis[10],

precipitation from solution[11], spray pyrolysis[12] and hydrodynamic cavitation[13], All

these techniques are based on the particle size, distribution morphology, purity and

degree of agglomeration .Spray pyrolysis produces the particle size near to 10 nm.

Narrow size distribution is not possible in majority of technique. Nanoparticles less than

10 nm can possible to be synthesized by precipitation in liquid medium but particles can

agglomerate. Chemical vapor condensation gives particle size 3-50 nm and its

continuous scale up is possible. The PTFE nanoemulsion can advantageously be

utilized as filler to create high performance materials assuring better homogenity, higher

contact surface, better rheological characteristics. Kapeliouchko et al [14] have

synthesized the nanoparticles with the help of microemulsion process. One of the

principal problem in using PTFE as filler is difficulty of adhesion with other materials. He

also developed the microemulsion polymerization together with various “core shell”

techniques which permits to obtain materials for the optimal use as high performance

filler.

The microwave plasma process is capable of producing nanoparticulate powders with

mean particle size in the range from 5 to 20 nm .The products may be oxides, nitrides,

sulfides, selenides or even materials. Additionally, it is possible to coat these particles

Ph.D.Thesis, Mr. Shriram Shaligram Sonawane, U.D.C.T. N.M.U., Jalgaon 2

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with a layer of second ceramic or a polymer. The resulting material is found to be the

super magnetic [15].

Skandan et al [16] described a method for the production of oxides nanopowder by

controlled thermochemical decomposition of metal organic precursor/carrier gas

mixtures in the low pressure flames, specially designed burner is used to achieve a flat

flame. Metal organic precursors introduced along with the fuel /air mixture experience

complete and uniform decomposition, thereby yielding a uniform synthesis of SiO2, TiO2

and Al2O3 nanophases. The product of ball milling of the magnetic and amorphous silica

(40-mole % Fe3O4) for an extended period of time in closed vessel has been

investigated by Koch et al [17]. It is found that the milling induces an extensive reduction

of Fe(III). The material constitutes a mixture of ultrafine Fe rich spinel particles

(magnetite/maghemite).Nanostructure oxides prepared, chemically have hydroxides as

intermediate precursor phases, therefore nanocrystalline oxides such as zirconia, titania

and magnesia system are prepared with sol gel technique. The temperature evolution

of hydrolyzed zirconium, titanium, and magnesium until they form the corresponding

nanocystalline oxides [18]. Al2O3 ceramics are important structure ceramics but α-Al2O3

is stable phase after calcination at high temperature, which easily promotes the growth

of grain powder and makes it difficult to get in nanoform, and other reason is Al2O3

particles get agglomerated during dehydration process. Considering the problem Wang

et al have prepared nanoscale α-Al2O3 powder with polyacrylamide gel method as

shown in figure1. Because polymer-network inhibits the aggregation of Al2O3 due to

which nanoscale α-Al2O3 powder with of size 10 nm can be obtained. Its calcination


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temperature is 11000C, which is 100 0C lesser than general calcinations temperature

use for other methods.

Fig 2.1: Nanosynthesis of Al2O3 by sol gel technique [8]

The microemulsion approach is a promising method to prepare nanometer size

particles. Microemulsion process technique can be employed for variety of the

chemicals such as Ag, ZrO2 and Ba, TiO2 etc., the nanometer sized titania particles

have been prepared by chemical reaction between TiCl4 solution and ammonia in the

reversed microemulsion system[19]. Nano-TiO2 whiskers were prepared through

controlled hydrolysis of titanium butoxide. The nano-TiO2 whiskers obtained were

anatase and

grew selectively in the (001) direction with a diameter of about 4 nm and length of about

40 nm. Acetic acid played an important role in the oriented growth of nano-TiO2

whiskers [20]. New development in the synthesis of nanometer scale TiO2 particles

have enabled the processing of existing new nanoparticles / epoxy composites. An


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ultrasonic method was used to disperse the nanoparticles in epoxy, thus this method

eliminates the need of solvent without sacrificing the ease of processing [21].

It is interesting to know that the transformation behavior from amorphous to anatase or

rutile phase is influenced by the synthesis condition. Most of the literatures show that

alkoxides based sol-gel or precipitation process yield amorphous titania precursors or

powders or powders with the anatase phase. [22-24 ]. At present there are few studies

on the preparation of nanodispersed titania powder from TiCl4 or Ti(SO4)2. Akhatar et al

[25-26] have investigated gas phase synthesis of Titania by TiCl4 oxidation in presence

of dopants. Ocana et. al.[27] obtained rutile TiO2 powder at 98 oC, using 3M TiCl4, for

measuring it’s IR and Raman spectra, but did not comment on fabrication method

production. Terwilleger et. al.[28] prepared the rutile phase TiO2 powder with an

average grain size < 20 nm by doping with small amount of Sn, which is the mixture of

SnO2 and TiO2 .

Manufacturing of TiO2 is possible with simplified and low cost continuous process, in

addition the Titania powder of anatase phase was prepared without calcination, with

particle size 4 nm reported by Zhang et. al. [29]. Nano structure materials with well

defined size are generally used in the catalyst and the chromatographic separation

processes. Brinker et al [30] described the production method for silica with the help of

rapid aerosol process. The evaporation of solvent during aerosol generation induces

multiphase assembly confined to an aerosol droplet containing polystyrene spears

silica, polystyrene spears /surfactant/silica or microemulsion silica. After removal of

surfactants, polymer spears, and microemulsion the resulting material exhibits

controlled meso-and macro-porosity [31]. Various routes used for production of the


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nano particles found some considerable disadvantages such as difficulty in handling

and processing of the nanoparticles. Number of workers [32-40] investigated novel

matrices for mediated control of CaCO3, K2CO3, CdS, CaSO4 Ca3(PO4)2, Mg(OH)2 which

are synthesized using matrix mediated growth technique like polyethylene oxide,

polyethylene glycol, polyvinyl acetate. Radhakrishan et al [41] reported that an increase

in ratio of polymer (PEG or PEO) gives considerable reduction in the nanosize

compared to the commercial available nanoparticles.

Nanostructure materials of perovsketite type oxides, LaMnO3, and LaCO3, have been

prepared by Min Chen et al [42]. They have used three different methods such as sol

gel, precipitation and amorphous complexometry observed the effect of the synthesis

methods on structure and catalytic activity, and tried to optimize the catalytic activity

of CO oxidation of LaMnO3.

A chemical Precipitation method has been implemented by Muhammed et al [43] for

synthesis of ZnO nanoparticles with controlled morphology. Several precipitation

reagents are used. Ammonium carbonate has also been used as precipitating reagent

which leads to unusual rod shape morphology, flow injection technique has been

developed to synthesize nanophase particles of zinc oxide. The average particle size of

ZnO obtained using the injection flow technique was of approximately 20 nm, while the

crystal size as measured by the X ray pattern was of 10-15 nm.

Ultrafine, equiaxed and monodipserse oxide particles with the average grain diameter

in the range of 1-10 nm have been prepared by Colinet et al [44] by two step chemical

approach; the chemical reduction of metallic salts obtained by activated sodium hybrids

in tetrahydronfuran solvent followed by oxidation of the metallic species with small


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amounts of O2-N2 gas. Such particles are easily, quantitatively and reproducibly,

prepared and are stable on the storage.

2.3 Preparation Methods of Mineral Clays and Polymer Nanocomposites

Polymer –clay interactions have been actively studied during sixties and the early

seventies. An oraganophilic clay showed dramatic improvements of mechanical, barrier

properties and the thermal resistance as compared with pristine matrix and at low clay

content (4 wt %). Since then the polymer –clay composites have been divided in the

three general types; i) Conventional composite where the clay acts as a conventional

filler, ii) Intercalated nanocomposite consists of regular insertion of the polymer in

between the clay layer and iii) Delaminated nanocomposites where 1nm thick layers are

dispersed in the matrix forming a monolithic structure on the microscale. Clay contains

the negatively charged layered silicates bound with metal cations such as Na+ or Ca++.

The clays are initially modified and then used. Modifications are done with the help of

surfactants, swelling agents to improve the surface properties of the polymers. Number

of authors have studied the systems of the polymer –clays such as clay polyimide [45],

clay-PP, [46-49],Na+ MMT clay Poly(vinyl alcohol) [50], smectic clay poly(methyl

methacrylate)[51],silicate-polyethylene oxide [52-53],clay-nylon[54-56],clay-epoxy[52],

clay-polyurethane[58], Clay-PS[59-60],polyaniline [61], clay-polybenzoxazole [62].

Manias et al [46] reviewed the PP/montmorillonite nanocomposites. The nano

composites are achieved in two ways either by using the functionalised PP and

common MMT clay or by using neat /unmodified PP and a semi fluorinated organic

modification for silicates. All the hybrids can be formed with solventless melt

intercalation or extrusion. Small addition less than 6 % of the nanoscale inorganic filler


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improves the properties such as the tensile characteristics high barrier properties better

scratch resistance and increasing flame retardancy.

Zr, Ti and Ti-Zr mixed oxides pillared montmorillonite (PILC) has been prepared

by Das et al [61]. MNT was used as a starting material and before pillaring, it was

subjected to exchange with Na+ ions, finally the additions of the respective samples

were treated with chlorides. They have used the prorled MNT-Ti samples for the

nitration reactions as the solid catalyst are generously employed. it was subjected to

exchange with Na+ ions, finally the additions of the respective samples were treated with

chlorides. They have used the prorled MNT-Ti samples for the nitration reactions as the

solid catalysts are generously employed.

2.3.1 Intercalation and exfoliation mechanism of polymer nanocomposites

Fig 2.2: Intercalation of polymer chains in nanoparticles layer

Two terms (Intercalation and exfoliation) are use generally used to describe the two

classes of nanocomposites that can be prepared. Intercalated structures are self

assembled, well ordered multi layered structure where in the extended polymer chains


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are inserted in to the gallery spacing between parallel individual silicate layers

separated from 2 nm to 3 nm (Fig 2).

The delaminated structure result when the individual silicate layers are no longer close

enough to interact with the adjecent layers. In the delaminated cases the interlayer

spacing can be of the order of the radius of gyration of the polymer, therefore the

silicate layers may be considered well dispersed in the organic polymers. The silicate

layers in a delaminated strucutre may not be well ordered as in an intercalated

structure. Both of these hybrid structures can also coexist in intercalated in the polymer

matrix; this mixed morphology is very common for composites based on smectite

silicates and clay minerals. X-ray diffraction measurements can be used to characterize

these nanostructures. Diffraction peaks in the low angle region indicate the d spacing

(basal spacing) of ordered intercalated and ordered delaminated nanocomposites ;

disordered nanocomposites shows no peaks in this region due to the loss of structural

registry of the layers and the large d spacing (> 100 nm)

2.4 Mechanical, Thermal, Physical and Rheological Properties of -

-Nanocomposites

The presence of a compatibilizer such as the Maleic anhydride grafted PP is important

for obtaining the improvements in the nanocomposites of clay. The important

characteristic is that the presence of the polar group of MAH-g-PP affects dispersion of

the clay layers in the composite and that is why it enhances the properties. Jog et al [62]

have studied the dynamic mechanical behavior, crystallization and morphological

behavior of PP-clay system. And found that the PP/clay system exhibits a disordered

structure from by XRD patterns. The thermal degradation temperature increases from


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270 to about 330 0C. DMA shows the significant improvements in the storage modulus.

The intensity of the loss modulus peak is reduced, showing weak cooperative relaxation

of PP in the PP/clay composites.

Polymeric nanocomposites based on the exfoliated organophilic layers of

silicates and polymer-mineral nanofillers exhibit the unique property profiles such as the

elevated heat distortion temperature combined with improved stiffness, strength, impact

resistance of elastomers, improved thermal stability, lower thermal expansion

coefficient, barrier against permeation of the gas and liquids rheological control and less

abrasion during the processing, reduced flammability [63].

Theoretical study of the tensile strength of the polymer-filler composites is

important aspect, Chow et al [64] have developed the predictive model which shows

that the tensile strength of a particulate-filled polymers which depends not only on the

volume fraction of the fillers and elastic moduli of two phases but also on the shape,

size and the interfacial adhesion of the filler particles and the matrix.

Polymer –graphite composites are of increasing attention due to their important

electrical properties. The need of the electrical and thermal conductivity of polymer

composites is in the electrical circuit boards and heat exchangers, Kripa et al [65] have

investigated thermal diffusivity and electrical conductivity of PP-graphite and HDPE-

graphite system (semicrystalline matrix), investigators used the graphite systems with

different particle sizes and specific surface area. Intercalated version offers the reduced

flammability benefits, but with less improvement in the physical properties, this issue is

still unidentified. Gilman et al [66] focused on mechanism of the flammability reduction

with recent results for PP-graft-Malic anhydride and PS-layered silicates


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nanocomposites using the MMT and fluorohectorite. Intercalated nanocomposites of

modified montmorillonite clay in glassy epoxy were prepared and studied by Zedra et al

[57]. Aliphatic diamine used as crosslinking agent. These materials found an

improvement in Young’s modulus but the corresponding reduction in ultimate strength

and strain to failure; the fracture behavior appears to be most dramatically improved in

the intercalated systems. The fracture energy increment was reported by 100% with

clay concentration of 5 wt %.

The effect of Nylon–6 molecular wt on the mechanical and rheological properties of the

nanocomposites formed from organically modified layered silicates by melt processing

has been extensively studied by the Paul et al [54]. Tensile modulus and yield strength

were found to increase with increasing concentration of clay while the elongation at

break was found to be decreasing; Izode impact strength was found to be independent

of the increase of the clay content for lower molecular wt. polyamides. Capillary and

dynamic parallel plate data revealed sizeable difference in the level of shear between

each nanocomposite system, mechanism for exfoliation during the melt mixing is

outlined. Organically modified silicates improve the barrier properties by exfoliation or

intercalation so alkyl–ammonium modified Montmorillonite, a biocompatible layered

silicate frequently used in cosmetics and food supplements.

Runt et al [61] Synthesized Polyurethane urea (PUU) with condensation reaction, and

found a considerable reduction in water vapors and oxygen permeability in PUU-PIB

comb polymers. They have invented significant reduction in the gas permeability with

simultaneous improvement in the mechanical properties, they have also achieved

concurrent property enhancement that could not be achieved with chemical modification


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of polyurethane polymers. The average mechanical properties for PUU/PUU layered

nanocomposites are summarized in Table 2.1.

Composites (Wt% Modified Silicate)

Modulus E50 (MPa)

Tensile Strength(MPa)

Elongation to break(%)

Neat PUU 3.380.21 27.4 2.9 80050

1 Wt % 3.930.34 31.4 2.3 890503 Wt % 4.340.48 31.4 3.2 950407 Wt % 4.960.34 32.1 1.4 10406013 Wt % 8.830.48 34.81.9 15050

20 Wt % 11.510.55 37.41.7 123070

Table 2.1: Mechanical Properties of PUU and PUU/ Layered Silicate nanocomposites

The nanodispersed silicates result in a significant increase in modulus, strength and

stiffness e.g. for the 20-wt % composite, by more than 300% and 30% respectively.

However, incontrast to conventional filled polymer systems, the increase in stiffness and

strength does not come at expenses of the ductility. A silica (Aeorsila200V) has been

functionalised by reaction with methacryl propyl trimethoxy silane (MPTMS)in toluene by

Guyot et al[62]. It has been found that functionalised silica gives very high elongation at

break.

Liu et al [67] prepared composites by grafting -melt compounding using a new kind of

co-intercalation organophilic clay which had larger interlayer spacing than ordinarily

modified alkali ammonium clay. One of co-intercalation monomers was unsaturated so

gives grafting reaction. Incorporation of silicate layers gives improvement in the storage

modulus and decrease of Tan δ value.


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Mechanical properties and crystallization behavior of the syndiotactic PP as

function of the silicate content has been studied by Mulhaupt et al [49]. Melt

compounding of s-PP with organohectorite, obtained via cation exchange of

fluorohectorite with octadecylammonium cation, it has been found that the Young’s

modulus has been increased five times with increasing content of the organophilic

silicate nanoparticles, the yield stress was increased in considerable value in the s-pp.

Styrene–clay nanocomposites were prepared by free radical polymerization of

styrene containing dispersed organophilic MMT, Fu et al [60] achieved the higher

dynamic modulus and higher decomposition temperature than pure polystyrene.

Due to formation of the aggregation of the nanoparticles and shear heating the melt

mixing of nanoparticles with high performance of the polymers is not possible. Jana et al

[68] investigated the feasible alternative solution to this problem, they used the lower

molecular weight polymer (epoxy) as reactive solvent and dispersing agent. They found

that there was considerable improvement in viscosity and processing temperature of

polyethersulphone (PES); there were considerable improvements in the barrier

resistance and heat deflection temperature over heats neat PES.

Nano TiO2-epoxy system has been developed by the Schelder et al [69], an ultrasonic

method has been used to disperse nanoparticles in epoxy composites. Composites

were processed at different loading, and exfoliated the exceptional strain to failure and

scratch resistance of the system.

The γ-Fe2O3 nano particles coated with DBS and CTAB were prepared by Liu et al

[70] by microemulsion process, the coated samples with surfactant showed the


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considerable enhancement in the nonlinear optical properties compared with their bulk

counter part.

The geometry and the orientation of the filler particles have significant influence on the

thermal conductivity of the composite material. Many of the theoretical treatments are

valid for only specific types of the filler particles and composite constructions, Bigg et al

[71] includes the theoretical calculations and the models predicted for the calculation of

the thermal conductivity of the spherical and the irregular shape fillers, long fibers and

flakes. Thermal conductivity and particle effect are not yet theoretically predicted.

The optical transparency of the PP-nanoparticulate composite with calcium

phosphate has been studied by Radhakrishanan et al [41], optical transparency of the

PP/nanoparticle composite was found much higher than the conventional calcium

phosphate samples.The vapor permeation of the silica nanoparticles was studied by

Dufaud et al [77]. This study characterizes the influence of the novel silica particles in

acrylate matrices on transport phenomena, the vapor permeation experiments confirm

the decrease in transport properties with the loading.

The Photovoltalic properties of nanostructure ZnO (Wurtzite) electrodes have

been investigated by Keis et al [73], photochemical studies were carried out on various

types of electrodes with controlled morphology of particle size and doping. The

monochromatic photon to current was recorded in the UV spectral region on bare ZnO

and in the visible region on the ruthenium dye sensitized cells. The results showed

relatively high efficiencies for such systems and demonstrated the potential of ZnO

nanostructure cells as materials for photovoltaic applications.


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Polymethyl methacylate filled silica particles of nanometric size were synthesized by

Hajji et al [74] using a five step procedure. Different types of materials were prepared by

changing the particle size (50 to 80 nm in diameter) and the weight fraction of silica (in

the range of 5-30 wt. %). Study of their swelling in chloroform showed that

tridimensional structure were likely to be formed, especially at high silica wt. fraction and

small particle size. As far as the thermo-mechanical properties are concerned, the main

relaxation temperature, T, was shown to be unaffected by changes in sample

formation, as expected the glassy modulus increased with the wt.fraction of silica, in

quite good agreement with the predictions of theoretical models. Finally the yield stress

behaviour was found to be related to a peculiar organization of the methylmethacylate

chains in the systems.

Model composites, consisting of an amorphous matrix (PMMA) filled with the

simple shaped nano particles of silica have been elaborated by Reynaud et al [75].

Three different ways an industrial route, a solvent technique with use of acetone and

mechanical alloying, and evolution of the dynamical mechanical thermal properties are

discussed with regard to the filler content. Eventually the comparison is drawn from 10

wt % filled systems, enlightening the elaboration influences on the microstructure. Caly-

polyimide(3,3’,4,4’-benzophenone tetracarboxylic dianhydride-4,4’-oxydianiline (BDTA-

ODA) nanocomposites were synthesized by Wai et al [45]. These nanocomposites were

synthesized from ODA modified MMT and poly(amic acid). Organoclay/BDTA –ODA

nanocomposites were synthesized via ODA-modified organoclay display large increase

in modulus and in maximum stress are observed as compared to pure BDTA-ODA. A

two-fold increase in modulus and a half fold increase in maximum stress in case of 7:93


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ratio of organoclay /BTDA-ODA. In addition the elongation at break of the organoclay

/BTDA-ODA nanocomposites is even slightly higher than the pure BTDA-ODA which is

in sharp contrast to that of conventional inorganic-filled polymer composites.

2.5 Flammability and Thermal Stability

Blumstein et al [1] reported the improved thermal stability of polymer clay

nanocomposites that combined Polymethylmethacylate (PMMA) and Montmorillonite

clay. A Clay–rich nanocomposite not only exhibits mechanical properties but also

enhances polymer thermal properties.

The Cone-Calorimeter is one of the most effective bench-scale method for studying the

flammability properties of material. The cone calorimeter measures fire relevant

properties such as heat release rate (HRR), and carbon monoxide yield, among others.

Heat release rate, in particular peak HRR has been found to be the most important

parameter to evaluate the safety. Gilman et al [66] have characterized the flammability

properties of a variety of polymer-clay nanocomposites, under the fire like condition,

using the cone calorimeter. The calorimeter data shows that both the peaks and

average HRR were reduced significantly for intercalated and delaminated

nanocomposites with low silicate mass fraction (2% to 5%). (Table 2)

Sample (structure)

Residual Yield (%) ± 0.5

Peak HRR(∆%) kW/m2

Mean HRR (∆%) kW/m2

Mean Hc

(MJ/ kg)

Mean SEA(M2/Kg)

Mean CO yield(Kg/Kg)

Nylon-66 1 1,010 603 27 197 0.01Nylon-66 silicate nanocomposit

3 686 390 27 271 0.01


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e 2% Delaminated Nylon –66 silicate –nanocomposite5% delaminated

6 378 304 27 2 96 0.02

PS 0 1,120 703 29 1,460 0.09PS Silicate –mix 3% immisicible

3 1,080 715 29 1,840 0.09

PS silicate –nanocomposite 3 %Intercalated /delaminated

4 567 444 27 1,730 0.08

PSW/DBDPO/Sb2O3, 30%

3 491 318 11 2,580 0.14

PP 0 1,525 536 39 704 0.02 PP silicate nanocomposite 2%Intercalated

5 450 322 44 1028 0.02

Table 2.2: Data sheet of thermal properties of different polymer Nanocomposites

2.6 Structural Characterization of Nanoparticles and Nanocomposites

2.6.1 Crystallization behavior study

Process history and use of temperature determine the relative fraction of the crystalline

polymer phases in the semicrystalline polymer composites, and thus have significant

influence on the stability of the crystalline region at the elevated temeperature. Vaia et

al [56] studied the influence of nanodisperesed MNT layer and process history on the

crystal structure of the nylon-6 between the room temperature and it’s melting. XRD and


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TEM have been taken in account to note the behavior. The temperature dependence of

total crystallinity and relative fraction of - and -phases imply that the -phase is

preferentially in the proximity of the silicate layers whereas the - phase exists away

from the polymer silicate interface region.Liu et al [48] studied the nonisothermal

crystallization behavior of polyamide –6/ clay nanocomposite (PA6CN) with the help of

differential scanning calorimeter (DSC) and X-ray diffraction (XRD). DSC results

showed that the nanometric silicate layer in the PA CN acted as an effective nucleating

agent. The addition of the silicate layers influenced the mechanism of nucleation and

the growth of Polyamide. It has been found that the addition of the silicate layers

favored formation of the crystalline form, the crystallinity degree of PA CN increased

with increasing cooling rate. Authors have also proposed a Non-isothermal kinetic

model.

The crystallization behavior of the syndiotactic PS-clay nanocomposite has been

investigated by Chang et al [76] The crystallization behavior of -and -crystals for

syndiotyactic PS nanocomposites has been investigated by the DSC and FTIR. The

results show that the presence of the clay plays important role in facilitating the

formation of the thermodynamically favorable form crystal when the s-PS is melt or

cold-crystallized.

2.7 Dynamic Heterogeneity

Numbers of the nanoscale system experiments have been done for the studies of

dynamical properties of the confined chains [77-81]. Fluids in nanoscopic confinement

posses a variety of unusual properties and in particular, remarkable dynamic


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hetrogenities, which varies on the length scale as short as a function of nanometer. Zax

et al [82] applied their efforts on the use of the nuclear magnetic resonance

spectroscopy to nanoscopically confined polystyrene (PS) created by the intercalation

into surface modified fluorohectorite. A comparison of surface-sensitive cross

polarization experiments with spin-echo experiments was also done; it has been

suggested that the PS in the center of nanopores is more mobile than the bulk at

comparable temperatures, while the chain segments which interact with the surface are

dynamically inhibited. Molecular modeling and rotational-isomeric-state model have

been used for initial confirmation of PS.

2.8 Surface Characterization

Polymer surfaces play an important role in their application such as adhesion, protective

coating, friction and wear, microelectronics and thin film technology. However up till

now the term surface has not been well defined because a surface defined by one

technique can be the bulk as revealed by another technique. Chan et al [83] used the

time flight secondary ion mass spectroscopy (TOF-SIMS), X-ray photoelectron

spectroscopy(XPS) and tapping mode atomic force microscopy(TM-AFM) to study

surface of the poly(N-vinyl-2 pyrrolidone) thin films containing nanoparticles. The study

XPS suggested that the concentration of the silica particles increases as the sampling

depth increases. TM-AFM phase imaging is shown to be capable of detecting the

presence of these sub-surface nano particles. Polymer dispersed liquid crystals (PDLC)

are important in development of electronic appliances. Bunning et al [84] have used the

small-angle X ray scattering and high resolution scanning electron microscopy for


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detecting the nano and mesoscale morphology of the polymer dispersed liquid crystal

films(PDLC) of varying the liquid crystal (LC) concentration.

2.9 Dispersion of Clay

It is well known that the dispersion of clay affects mechanical and thermal

characteristics of the nanocomposites, means degree of the dispersion of clay decides

the properties of nanocomposites. Small-angle neutron scattering (SANS) is excellent

tool to prove the degree of separation or dispersion exchanged clay mineral in a

solvent. Hanley et al [85] has used SANS to investigate the dispersion in toluene of

various forms of the cloisite C-15A complex.

2.10 Rheological Behaviors of Polymer Nanocomposites

The rheological properties of insitu polymerized nanocomposites with end –tethered

polymer chains were first described by Zax et al [82].

Recently polymer/clay nanocomposites with polyaniline and styrene/acrylonitrile

copolymer have been introduced as candidate materials for drybas electro-rheological

(ER) fluids. In ER application, there rheological properties of dispersed clay polarizable

colloidal suspension under external electric field strength change abruptly via structural

change in the particle aggregation in either chain or column like structures. Kim et al

[51] studied the strongly hydrophobic PS was intercalated into the hydrophilic silicate

layers via emulsion polymerization which has been previously sued to produce

nanocomposites consisting of poly( metyl methacrlate), polyaniline or syrene


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/acrylonitrile copolymer and Na+- MMT are filled with sodium cations , the hydrophilic

properties are enhanced and lead to a high degree of swelling in water.

2.11 Polyamide 66 Clay Nanocomposites

Polymer/organoclay nanocomposites present unique properties that are not observed in

conventional composites. Incorporation of small amounts of organoclay (<10wt.%) into

polymer matrices may remarkably improve dimension stability, mechanical, thermal,

optical, electrical, and gas barrier properties, and decrease the flammability. This

happens due to the large contact area between polymer and clay on a nanoscale as

reported on literature [1–11]. The incorporation of organoclays into polymer matrices

has been known for 50 years and one of the pioneering works was from Toyota as

reported by Cho and Paul [87]. To be compatible with polymer matrices, sodium

smectite clays need to be modified by using quaternary ammonium salts with at least 12

carbon atoms in aqueous dispersions. In these dispersions, the clay particles or layers

must be separated one from another and not be stacked in order to facilitate the

introduction of the organic compounds. As a result, the clay exchangeable cations are

replaced by the organic cations of the quaternary ammonium salt that are adsorbed on

the negative sites of the clay surfaces. The obtained clay is known as organoclay [7–

12]. Polyamide 66 (PA66) is an important engineering plastic, but PA66 matrix

nanocomposites have been little investigated by researchers up to now [13–15]. The

Na-MMT clay can be modified organically (named as organoclay) with quaternary

ammonium salt according to the procedure [16].


Literature Review

2.12 Structure of PA66/Clay Nanocomposites.

Figure 3 presents the X-ray diffraction patterns for the PA 6,6 systems with 2 wt.% of

unmodified (MMT) and modified clay (OMMT). The interlayer distance was determined

by the diffraction peak in the X-ray method using the Bragg equation. It can be

observed for the modified clay (OMMT) three peaks corresponding to an interlayer

spacing d001 of 29.2, 19.2, and 12.5 A° . The two first peaks indicate that the

intercalation of the salt between the layers of clay has occurred. According to the

literature [91, 92] another peak corresponds to interlayer spacing’s of 12.5A° (d001 for

unmodified clay-MMT) is probably due to an incomplete ion exchange, with some

residual Na-MMT remaining in the material. . The results indicated that the quaternary

ammonium salt was intercalated between two basal planes of OMMT leading to an

expansion of the interlayer spacing. It can be observed for PA6,6/MMT system a

diffraction peak around 14.71 A° , which is close to the distance of 12.5 °A of the

unmodified clay indicating that the increase of the basal spacing practically did not

occur. On the other hand, the sample of the nanocomposites of PA6,6 with the modified

clay (OMMT) presented the displacement of the XRD peak toward a lower angle values,

which represents an increase to 19.20 °A in the basal spacing. It can be thus noticed

that with the organoclay presence, the peak related to the PA66/unmodified clay

interlayer spacing disappeared and a new broad diffraction peak appeared. This peak

may be due to the intercalation/partially exfoliation of the polymer chains between the

layers of organoclay. These results were be confirmed by TEM. Figure 4 shows the

TEM images of the PA66 system. In Figure 3(a), it can be seen clearly agglomerates of


Literature Review

clay and in Figure 3(b) exists intercalated clay layers but it can be seen too several

exfoliated clay layers present in the PA6,6 matrix. Therefore, the obtained PA66/OMMT

systems are partially exfoliated nanocomposites according to the XRD pattern (Figure

4) and the literature [86-92 and 98-100].

Figure 2.3: XRD patterns of montmorillonite clay modified with Praepagen salt (OMMT),A66/MMT, and PA66/OMMT nanocomposites. [101]


Literature Review

Figure 2.4: TEM photomicrographs of (a) PA66/MMT and (b) PA66/OMMT Nanocomposite.[101]


Literature Review

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Chapter II

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