DOI 10.1515/revce-2013-0014      Rev Chem Eng 2013; 29(6): 439–448

Vinay Kumar * and Amandeep Singh

Polypropylene clay nanocomposites Abstract: Various polymers such as nylon, polypropylene,

polystyrene, ethylene vinyl acetate, epoxy resins,  poly-

urethanes, polyimides, and polyethylene terephthalate

can be reinforced by adding nanofillers with dimen-

sions < 100 nm. Fillers can be in the form of particles (min-

erals), sheets (exfoliated clay stacks), or fibers (carbon

nanotubes or electrospun fibers). Polypropylene and clay

are most widely used components for making nanocom-

posites. For proper dispersion of clay with polypropylene,

maleic anhydride polypropylene is commonly used. The

composites thus prepared have applications in food pack-

aging, structural, chemical, electrical/electronic, and

medical fields.

Keywords: maleic anhydride polypropylene (MAPP);

nano clay; polypropylene; structural.

*Corresponding author: Vinay Kumar, Sant Longowal Institute

of Engineering and Technology (SLIET), Department of Chemical

Technology, Longowal, Punjab 148106, India,

e-mail: vinay652001@yahoo.co.in

Amandeep Singh: Sant Longowal Institute of Engineering

and Technology (SLIET), Department of Chemical Technology,

Longowal, Punjab 148106, India

1 Introduction Polymers are widely used since more than a century

ago. Because of their important properties (such as light

weight, good insulation, water resistance, easy process-

ing), their usages have expanded in packing, automobile,

aerospace, and construction sectors. The properties of

polymers can be modified by adding fillers and fibers to

meet specific requirements. In the last decade, the atten-

tion of scientists has shifted on the use of nanomaterials

to reinforce polymers to enhance their properties for a

variety of applications.

Nanocomposites are available in nature such as in

abalone shell and bone structures. Since the mid-1950s,

nanoclays have been used to control the flow of polymer

solutions and constitution of gels. In the 1970s, polymer

clay composites were discussed in textbooks, but nano-

composites were not in common use ( Nanocomposite

Information 2013 ). A nanocomposite is a multiphase solid

material where one of the phases has one, two, or three

dimensions of < 100 nm or structures having a nanoscale

repeat distance between different phases ( Nanocomposite

2013 ). Nanocomposites differ from conventional compo-

site materials owing to the exceptionally high surface-

to-volume ratio of their reinforcing phase and/or their

exceptionally high aspect ratio.

The commonly used polymers that can be modified

with nanofillers are nylon, polypropylene (PP), polyethy-

lene (PE), polystyrene, and ethylene vinyl acetate (EVA),

epoxy resins, polyurethanes, polyamides, and polyethy-

lene terephthalate (PET).

There are different types of nanoparticles that

can be used in a polymer matrix to form polymer

nanocompo sites. Nanofillers can be made up of parti-

cles (minerals), sheets (exfoliated clay stacks), or fibers

(carbon nanotubes or electrospun fibers). The most

commonly used nanofillers are montmorillonite (MMT),

carbon nanofibers, polyhedral oligomeric silsesquiox-

ane, carbon nanotubes (multiwall nanotubes, small

diameter nanotubes, and single wall nanotubes), nano-

silica, nanoaluminum oxide (Al 2 O

3 ), and nanotitanium

oxide ( Baksi et al. 2008 ).

Nanofillers are available in solid form and generally

comprise inorganic materials and rarely organic materi-

als. The performance of fillers depends on the formation

of chemical bond and disruption of conformational posi-

tion of polymer matrix. Immobilization of adjacent mole-

cule groups and the orientation of the polymer also affect

the filler performance. Nanoparticles have an extremely

high surface-to-volume ratio, which dramatically changes

their properties when compared with their bulk-sized par-

ticles. Nanocomposites show improvement in mechanical

properties (tensile strength, stiffness, and toughness),

barrier properties, and flame retardancy. They outperform

standard fillers and fibers in terms of heat resistance,

dimensional stability, chemical resistance, and electrical

conductivity. There are optical issues and dispersion dif-

ficulties with nanofillers that need to be improved.

Nanocomposites have excellent barrier characteris-

tics useful in food packaging applications (flexible and

rigid). Addition of small quantities of nanoclay improves

the gaseous barrier property (oxygen transmission rates

for polyamide is reduced by the addition of organoclay).

Addition of nanoclay enhances transparency and shelf life

and reduces haze. Epoxy-reinforced nanocomposites are

used in structural applications. PP can be reinforced with

440      V. Kumar and A. Singh: Polymer composites

carbon nanotubes to produce windmill blades that increase

the amount of electricity generated by windmill (due to

longer blades). Addition of graphene to epoxy composites

gives stronger and stiffer components because of effective

coupling. High strength-to-weight ratio of this material is

useful in aircraft components. Silicon nanospheres and

carbon nanoparticle-based composites are used for making

anodes for lithium ion batteries. These anodes make the

contact with the lithium electrolyte closer and allow faster

charging or discharging of power. Polymer nanotubes-

based composites conduct electricity depending on the

spacing of the nanotubes. They are used as stress sensors

in windmill blades, triggering an alarm and thus prevent-

ing damage ( Boysen 2009 ).

The use of nanoclay reduces solvent transmission

through polymers (polyamides). This property is useful

for the fuel tank and fuel line components for cars. Nano-

clay works as a nucleating agent to control foam cell

structure. Addition of 5% nanoclay to foamed low-density

polyethylene decreases cell size, increases cell density,

and facilitates foam expansion. A nanotube polymer com-

posite, when used as a scaffold, speeds up the growth of

the replaced bone. The flame-retardant behavior of PP

is improved with 2% nanoclay loading. The heat release

rate diminishes substantially by nanoclay addition. Nano-

clay incorporation causes a significant reduction of water

absorption in the polymer.

PP is a useful thermoplastic polymer. The higher crys-

tallinity in PP is due to its regular geometrical shape. It

has an intermediate level of crystallinity between low- and

high-density polyethylene.

PP is a lightweight polymer with good mechanical,

electrical, and chemical properties. It has good tensile

strength and strong resistance toward stress cracking.

Excellent insulation properties are useful for various elec-

trical applications. It remains unaffected by alkaline sub-

stances, acids, degreasing agents, and electrolytic attacks.

In our daily life, PP is used in various house wares.

Food containers made of PP are of superior quality and

can be safely washed in a dishwasher. It is used for

making cans and syrup bottles for food packaging. In

textile, colorful fibers of PP make beautiful carpets with

high durability. In the automotive sector, the use of PP

has expanded to auto parts such as bumpers and battery

cases. It does not promote bacterial growth on its surface

and is therefore useful in various medical equipments. In

the construction sector, it is used in the manufacturing

of pumps and different types of pipes. Other important

applications are in packaging, labeling, stationery, labo-

ratory equipment, and polymer banknotes ( Mukherjee

2012 ).

Nanocomposites based on layered inorganic com-

pounds such as clays are in wide use owing to their high

mechanical strength and good thermal resistance. The

type of clay and its pretreatment method, the selection

of the polymer component, and the method of incorpo-

ration of clay have significant effects on nanocomposite

properties. The purity and dispersion of clay also affect

nanocomposite properties. Polymers and clays are non-

miscible due to the difference in their polarity. Clay polar-

ity needs to be changed to organophilic to successfully

form polymer clay composites, and this can be carried out

using swelling agents such as surfactants, which increase

the interlayer distance of the clay structure before it is

mixed with the monomeric material then polymerized in

the presence of clay to form nanocomposites. A clay-based

nanocomposite can be produced in form of an intercalated

or exfoliated structure. In intercalated nanocomposites,

the organic component is inserted between layers of clay

such that the interlayer spacing is expanded, but layers

still bear a well-defined spatial relationship to each other.

In an exfoliated structure, the layers of clay are completely

separated and individual layers are distributed through-

out the organic matrix.

Nanoclays modify the properties of polymers such

as nylon 6, EVA, epoxy, PET, PE, and PP. Improvement

in clarity, stiffness, thermal stability, barrier properties

(moisture, solvents, vapors, gases, and flavors), chemi-

cal properties, flame resistance, scratch resistance, and

dimensional stability is noted. Nanomer and Cloisite are

the popular nanoclays available in the market, and 0.5%

to 10% of these nanoclays can be used. The superior prop-

erties of these materials can match metal, glass, and wood.

The two main challenges in developing nanocompos-

ite materials are the following:

– The use of nanoparticles requires an interfacial

interaction and/or compatibility with the polymer

matrix.

– Processing technique should offer uniform dispersion

and distribution of nanoparticles.

2 Polypropylene nanoclay composites

2.1 Dispersion effect of clay on nanocomposites

Nam et  al. (2001) prepared polypropylene nanoclay

(PPNC) composites using maleic anhydride polypropylene

V. Kumar and A. Singh: Polymer composites      441

(MAPP) and organophilic clay. It was revealed that with

higher clay loading, more MAPP chains were intercalated

in the nanocomposites. After crystallization at 80 ° C, a

crystalline texture was obtained, which comprises inter-

febrile structures including phase crystallite. Wang et al.

(2004) used various types of MAPPs such as PB3150,

PB3200, PB3000, and E43 of different maleic anhydride

(MA) contents and molecular weights ( M r ). MAPP com-

patibilizers gave a similar degree of dispersion beyond the

3:1 weight ratio, with the exception of E43. The intercala-

tion capability of the compatibilizers in clay layers and the

composition of the compatibilizer in PP/clay composites

helped in the exfoliation and homogeneous dispersion of

clay layers. The formation of complete hybrids took place

when the intercalation capability of MAPP has a MAPP/

clay weight ratio > 3:1. Shaobo et al. (2010) used transmis-

sion electron microscopy (TEM) and optical microscopy to

find the degree of dispersion ( χ ) and the mean interpar-

ticle distance per unit volume of clay ( λ V ). The degree of

dispersion is the percentage of exfoliation and λ V is the

measure of the spatial separation between particles rela-

tive to clay loading. PPNC 8 had a much lower χ value than

PPNC 10.5, due to its lower loading of compatibilizer. A

better dispersion of clay particles in PPNC 10.5 resulted in

a higher storage modulus and a complex viscosity at low

frequencies. Rousseaux et  al. (2010a) used carboxylate

clays to synthesize PPNC. Carboxylate salts partially neu-

tralized the MA groups of MAPP, and the resultant ionic

groups of the partially neutralized polymer have a good

interaction with clay. The three carboxylate salts used

were sodium acetate, sodium propionate, and sodium

butyrate. A higher basal spacing was obtained while inter-

calating sodium acetate into the silicate layers. Nanocom-

posites, with the addition of clay and trihydrated sodium

acetate, exhibited the best thermal and rheological prop-

erties owing to good dispersion. Rousseaux et al. (2010b)

used a water-assisted extrusion process to prepare PP

clay composites using MAPP. Thermal, mechanical, and

rheological properties were also good in these composites

owing to better clay dispersion.

2.2 Mechanical properties of PPNC composites

Morgan and Harris (2003) studied the effect of Soxhlet

extraction times of organoclays on the properties of

PPNC. Higher flexural modulus, better clay dispersion,

delayed ignition time, and lower heat release rate were

obtained through the removal of excess organic treat-

ment. Higher extraction times gave better clay dispersion

and collapse of d-spacing, resulting to better impact

strength. A delayed ignition temperature was observed

through the removal of extra organic treatment. Garc ı

et  al. (2003) prepared PP clay nanocomposites using

diethyl maleate (DEM) and MA. The clays used were MMT

and sodium bentonite that were purified and modified

with octadecylammonium ions. Commercial clay outper-

formed octadecyl ammonium-treated bentonite in these

composites. Using DEM, the differences in the mechani-

cal properties of clay-modified composites were smaller.

DEM has a lower polarity compared with MA and therefore

has less effective interaction with the polar components

of clay. MA has a high reactivity toward a modifying agent

than to DEM. Chung (2005) reinforced isotactic PP with

terminal functional groups such as OH, Cl, NH 2 , OH, and

+

3NH using nanoclay. Cations led to formation of hydro-

gen bond and were located between clay interlayers. Such

interactions anchor the PP chain to the clay surface and

the remaining high-molecular-weight PP tail exfoliated

clay layers. Therefore, polymers with reactive functional

groups can be used as polymeric surfactants for the syn-

thesis of exfoliated PPNC.

The impact behavior of PP clay nanocomposites was

studied by Yuan and Misra (2006) . A higher impact strength

was reported in the 0 ° C – 70 ° C range, but impact strength

remains unaffected below 0 ° C using clay. Crystal structure,

dispersion state, and interfacial interaction were the factors

responsible for the change in impact behavior of PPNC.

Bureau et  al. (2006) reinforced PP with organo-modified

clays using different MAPPs. Tensile strength improved sig-

nificantly due to the reinforcing effect of the nanoparticle.

Improvement in toughness was due to improved matrix

resistance attributed to finer, more oriented clay nanoparti-

cles. TEM analysis showed good clay intercalation level and

partial clay exfoliation. The M r of MAPP has an effect on

the quality of clay particle dispersion, and a low M r gener-

ally leads to better clay dispersion. Kim et al. (2007a) used

organoclay in PP with MAPP as compatibilizer. The aspect

ratio of the clay particles decreased with clay loading but

increased with MAPP loading. A better percolation network

was found by increasing the number of the organoclay par-

ticles in fixed ratio of MAPP to organoclay. A higher MAPP

loading lowers the modulus and crystallinity but increases

polymer expansion. PP organoclay nanocomposites were

prepared by a two-step master batch compounding as

studied by Dong et al. (2008) . The percentage of the organo-

clays was from 1 and 10 wt% using MAPP. A computational

model by object-oriented finite element analysis code has

good agreement with experimental data and theoretical

results for studying mechanical properties. Lai et al. (2009)

used polyolefin elastomer-grafted maleic anhydride and

442      V. Kumar and A. Singh: Polymer composites

polypropylene-grafted maleic anhydride (PP-g-MA) com-

patibilizers in an organoclay PP composite. The MAPP-mod-

ified composite had higher transmittance. It also enhanced

the tensile strength, cutting strength, and Young ’ s modulus

of the composite. The addition of POE-g-MA is more effec-

tive, compared with MAPP, in terms of interlayer spacing.

The properties of the PP nanocomposites were optimized

using quaternary ammonium salt in the MMT studied by

Santos et al. (2009) . A higher impact strength was obtained

with C-15A [high cation exchange capacity (CEC)], whereas

with C-20A (low CEC), a better flexural modulus resulted.

The dispersion of clay was more homogeneous without

agglomerated structures with both salts. The modulus of

PP nanocomposites was better, but glass transition tem-

perature (T g ) decreased slightly. Dong and Bhattacharyya

(2010a) used scanning electron microscopy (SEM) and

TEM to gather geometric information regarding mapping

of micro/nanostructures. The elastic moduli of PPNC

were compared based on experimental data and theoreti-

cal models and were found to be in very good agreement.

The orientation of clay particles affected the elastic moduli

of PPNC composites. Clusters of clay can led to localized

stress concentrations, resulting to easy failure of the nano-

composite. Dong and Bhattacharyya (2010b) prepared

two-dimensional 3 × 3 array representative volume element

model to study the mechanical properties of PP/organoclay

nanocomposites. Exfoliated nanocomposites had higher

elastic moduli as compared with intercalated counterparts.

Interphase properties had a less significant effect on the

modulus of exfoliated nanocomposites than intercalated

ones. The empirical relationship E m

< E i < 2E

m had resulted

for the interphase modulus of intercalated PP/organoclay

nanocomposites using MAPP as a compatibilizer. Pettarin

et  al. (2010) studied the nucleating effect of nanoclays

Layeredclay

Polymer

Intercalatednanocomposite Exfoliated

nanocomposite

Figure 1   Formation of intercalated and exfoliated nanocomposites

from layered silicates and polymers ( Hay and Shaw 2001 ).

in semicrystalline polymers. Nanofillers improved the

elastic modulus and hardness in the skin layer. A marginal

improvement of the dynamic friction coefficient was seen,

whereas the static friction coefficient was not affected.

Addition of layered clay in polymer gives two types of struc-

tures: intercalated and exfoliated as shown in Figure 1.

Ferreira et al. (2011) prepared PP nanocomposites with

nanoclay by injection molding, and the effect of surface

treatment was studied. Surface treatment of nanoclay

increased the stiffness, tensile strength, and impact energy.

In fatigue analysis, materials exhibited high strain accu-

mulation and stress release, resulting to lower fatigue per-

formance than unfilled polymer. The smaller particle size

of the nanofiller resulted to a fatigue performance close to

virgin polymer. Soleimani et al. (2012) studied the mechan-

ical behavior of nanoclay-filled PP composites modi-

fied with MAPP at room and cryogenic temperatures and

observed an improvement in Young ’ s modulus and impact

strength at both room and cryogenic temperatures. Klitkou

et al. (2012) studied PP reinforced with organically modi-

fied montmorillonite (OMMT) using MAPP on twin-screw

extrusion. The process was repeated a number of times

to enhance extruder residence time (TR) and particle dis-

persion. The Carreau-Yasuda model showed that particle

dispersion increase with TR. Tensile strength and modulus

remained unchanged with TR but Izod impact increased

with higher TR. Higher fracture initiation and propagation

energy were noted in composites. Drozdov and Christiansen

(2012) prepared isotactic PP modified with organically

nano clay. The use of 2% clay resulted in a strong reduc-

tion of the maximum and minimum strains per cycle and

sample failure took place at higher number of cycles as

compared with virgin PP. A constitutive model explained

that fatigue failure is driven by a pronounced increase in

plastic strain in the crystalline phase. This model is useful

in predicting the evolution of stress-strain diagrams with

a number of cycles. Boumbimba et al. (2012) studied the

high strain rate compressive yield stress of PP organoclay

nanocomposites. A three-phase approach was proposed,

which is based on the micromechanical formulation of a

cooperative model for yield behavior of semicrystalline

polymers. The result from the Split Hopkinson pressure

bar apparatus showed that yield stress was sensitive to

strain rate, temperature, and organoclay concentration.

It was significantly affected by the extent of exfoliation.

Pettarin et  al. (2013) studied the fracture performance of

PPNC composites with box-like shape. The initial crack

was branched and deviated out of plane normal to applied

stress. An increase in nanoclay content led to higher ductil-

ity. The nanoclay content did not affect fracture initiation

but increased the energy propagation release rate.

V. Kumar and A. Singh: Polymer composites      443

2.3 Thermal properties of PPNC composites

Liu and Wu (2001) used clay with large interlayer spacing

to reinforce PP. Addition of clay accelerated the crystal-

lization process, resulting to a higher storage modulus

but with lower tan δ and Tg. Zhang et al. (2004a) prepared

PPNC using swollen organoclay. Organoclay was treated

with a swelling agent (maleic anhydride) and a co-swelling

agent. Clay was melt-blended with MAPP to obtain a pre-

intercalated composite (PIC); it was further blended with

PP to produce PPNC. The basal spacing of pristine clay

treated with MA was larger than original clay but smaller

than organoclay. The clay layers in the pre-intercalated

blends were stacked in an orderly manner, and a partial

exfoliation of clay layers was found. A good dispersion of

clay layers improved the thermal stability, Tg, and storage

modulus of PPNC. Zhang et  al. (2004b) prepared PPNC

using organoclay, which was modified with MA using a

co-swelling agent and an initiator. X-ray diffraction (XRD)

showed that the basal distance in MA-modified organo-

clay was larger than original organoclay. Layers of clay

were partially exfoliated in grafting-intercalating com-

posites and were fully exfoliated in PPNC. Better thermal

stability, Tg, and storage modulus was obtained due to

the reinforcing effect of clay. Diagne et al. (2005) prepared

PP MMT nanocomposites using MAPP through extrusion

and injection molding. The injection-molded samples had

exfoliated structures, whereas extruded samples had both

exfoliated and immiscible structures. Thermal stability

and fire retardancy of nanocomposites increased at 5%

clay loading, and improvement was higher in injection-

molded samples. The onset temperatures of degrada-

tion and peak heat release rate decreased with ageing

time for nanocomposites. Outstanding improvement in

fire properties was found in UV-irradiated MAPP-treated

samples. PP/clay nanocomposites were studied by Perrin-

Sarazin et al. (2005) using MAPP. A better clay dispersion

was achieved using MAPP due to higher particle surface

density at microlevel, submicrolevel, and nanolevel. Low-

M r MAPP interacted well with clay particles, resulting in

good and uniform intercalation. Higher- M r MAPP led to

heterogeneous intercalation with signs of exfoliation.

Fine clay dispersion with MAPP resulted to crystallization

at lower temperature and at a lower rate.

Yuan et  al. (2006) studied the influence of different

concentrations of clay nanoparticles on isothermal crys-

tallization behavior of PPNC composites. The crystalliza-

tion peak temperature (T p ) of PPNC improved marginally

as compared with virgin PP at different cooling rates.

The half time for crystallization decreased with clay

loading due to nucleation. A lower activation energy for

crystallization of PPNC confirmed the nucleating effect of

clay. Wang et al. (2006) studied the effects of the organ-

oclay network on mobility and relaxation in isotactic

polypropylene (iPP). A three-dimensional filler network

structure was formed in polymer/layered silicate nano-

composites at threshold clay loading. Higher filler loading

gave low melt fluidity, retard crystalline capability, and

enhanced thermal stability. Baniasadi et  al. (2010) used

bentonite clay to reinforce PP by intensity polymerization.

An improvement in thermomechanical properties of com-

posite was noted due to significant exfoliation of clay. A

higher filler loading resulted to better storage modulus,

thermal stability, and crystallization temperature (T c ),

but elongation and impact strength decreased. The use of

clay gave higher yield strength and tensile modulus due

to the brittle nature of in situ polymerized sample. Perez

et al. (2010) studied PP nanocomposites prepared on co-

rotating twin-screw extruder using MAPP. No change in

melting temperature (T m

) and degree of crystallinity (X C )

of composites was found with the addition of clay and

MAPP, but thermal stability, heat deflection temperature

was higher. A higher modulus was obtained with equal

loading of nanoclay and MAPP. Dayma and Satapathy

(2010) studied ternary nanocomposites based on polyam-

ide-6 (PA)/PP using MAPP and organoclay. The crystal-

linity of the nanocomposites remained unaffected, but a

higher glass transition temperature (T g ) accompanied by

the appearance of a second-phase T g peaking progres-

sively at higher temperatures was obtained, confirming

the reinforcement effects. A substantial improvement in

elastic modulus and flexural modulus while maintain-

ing impact strength of composites was found. The failure

mode of nanocomposites changed from interfacial effect-

assisted fibrillation-controlled ductile deformation to

nanoclay-induced soft PP phase-stiffened semi-ductile

response. Canetti et al. (2012) reinforced PP by nanoclay

in the presence of a hydrogenated oligo-cyclopentadiene

(HOCP) compatibilizer. The use of HOCP favored the homo-

geneous dispersion of nanoclay in PP. Thermomechanical

degradation during processing was improved using HOCP.

The thermal resistance of compatibilized nanocomposite

was higher and the thermal degradation process shifted

to a higher temperature. Tensile modulus and elongation

of compatibilized nanocomposite was similar to pure PP.

Fina et al. (2012) studied the flaming ignition properties

of PPNC composites using cone calorimetry. PP showed

an increase in ignition temperature with increasing

imposed heat flux, which is explained by the reduction

in oxygen availability for polymer decomposition. Sig-

nificant changes in PP evolution were observed compared

with PET. PP ignition was due to the decomposition of

444      V. Kumar and A. Singh: Polymer composites

a relatively thin surface layer, whereas an almost whole

specimen thickness takes part in production of volatiles

in case of PET. Accumulation of clay by migration and/or

polymer ablation played a role in the diffusion of oxygen,

controlling ignition at low imposed heat flux.

2.4 Rheological properties of PPNC composites

Mark and James (2007) studied the effect of organoclay

loading and MAPP on rheology of PPNC. Small ampli-

tude oscillatory shear indicated the difference in clay

silicates delamination for fixed organoclay loading. The

use of MAPP compatiblizer increased storage modulus.

A lower MAPP concentration did not influence solid-like

rheology over time through network formation. Wang

et  al. (2007) prepared iPP/organoclay nanocomposites

by melt blending. Alignment induced by large amplitude

shear and stress relaxation was useful for estimating the

orientation capability of nanocomposites. The rheologi-

cal response to shear and disorientation kinetics affected

the orientation and tensile strength of composites.

Drozdov et al. (2009) prepared PP/clay nanocomposites

and studied rheological properties such as viscoelasti-

city, viscoplasticity, and creep failure. Viscoplasti city

was associated with deformation-induced sliding of

junctions in network. The use of nanoclay (1 wt%) gave

the best Young ’ s modulus, creep resistance, and yield

stress. Mahmoud (2011) synthesized PP/clay nano-

composites on a twin-screw extruder. Addition of clay

to PP enhanced storage modulus and viscosity due to

the exfoliation of clay. Costantino et al. (2012) observed

that better mechanical properties were obtained by high

levels of intercalation, exfoliation, and dispersion of

nanoclay. For proper processing of nanocomposites, a

sufficient stress level was required, which was possible

through the shear-controlled orientation method or by

changing the melt temperature and shear time.

2.5 Crystallization behavior of PPNC composites

Ray et al. (2007) used the ultrafast scanning calorimetric

technique to study the crystallization behavior of compo-

sites. A higher clay loading increased the crystallization

rate because of the nucleating effect, but crystallization

rate decreased with 10% clay loading because it hindered

the crystallization of the polymer chains. Few compos-

ites in the 75 ° C – 85 ° C temperature range showed a double

peak during isothermal crystallization, which indicated

the simultaneous occurrence of fast and slow crystalliza-

tion processes. At temperatures higher than 120 ° C, clay

slightly retarded the crystallization process.

2.6 Permeability behavior of PPNC composites

Chinellato et  al. (2010) prepared PP/organoclay nano-

composites using an acrylic acid-grafted polypropylene

(PP-g-AA). Wide-angle X-ray scattering and TEM showed

that OMMT was better dispersed in the presence of PP-g-

AA, and its interlayers were intercalated and partly

exfoliated by polymer chains. Addition of organoclay

decreased CO 2 permeability for all samples, and signifi-

cantly so for compatibilized samples. Samples with a

compatibilizer/organoclay ratio of 5:1 had better barrier

properties.

2.7 Influence of electron irradiation on PPNC composites

Misheva et al. (2008) reinforced PP with nanoclay using

MAPP as compatibilizer. The influence of different doses

of electron irradiation was studied. A decrease in ortho -positronium ( o -Ps) intensity indicated a small increase in

free volume due to the addition of clay and MAPP, which

is attributed the formation of carbonyl groups during irra-

diation. The use of MAPP resulted to a higher standard

Vickers microhardness (MHV), whereas electron irradia-

tion drastically decreased MHV.

2.8 Hybrid PPNC composites

Dongyan and Charles (2003) reinforced PS and PP with

nanoclay using the melt-blending process. Clay was not

uniformly distributed in the polymer, but the polymer

was inserted between clays. A lower heat release rate con-

firmed the formation of nanocomposites. The use of MAPP

enhanced intercalation within nanocomposite. Chow et al.

(2003) synthesized a blend of PA6 and PP with organo-

clay using MAPP. The synergistic effect of organoclay and

MAPP improved the strength and stiffness of the PA6/PP

blend. Addition of clay increased stiffness but reduced

ductility due to exfoliation and intercalation. H-bonding

between amine groups of clay and carbonyl groups of PA6

favored the exfoliation of organic clay. Su et al. (2004) used

organically modified clays containing oligomeric styrene

or methacrylate to reinforce poly(methyl methacrylate),

PP, and PE. Styrene-based clay allowed direct blending

V. Kumar and A. Singh: Polymer composites      445

with PP without needing maleation. Both clays had better

thermal stability compared with ammonium salts. Higher

degradation temperature and melt processing at a higher

temperature were noted in composites.

Nanocomposites of PE and PP showed a variation in

impact behavior in the -40 ° C to 70 ° C temperature range

studied by Deshmane et  al. (2007) . Impact strength

increased in PP by the addition of nanoclay, whereas it

decreased for PE. Strong PP clay interaction and better

nucleating effect of clay resulted in a significant change

in crystallization temperature, glass transition tempera-

ture, intergallery space, and spherulite size. Kim et  al.

(2007b) prepared thermoplastic olefin (TPO)-based

nanocomposites using MAPP. With an increase in the

loading of clay and MAPP, the aspect ratio of the elas-

tomeric phase increased because the elastomeric parti-

cles became highly elongated. Higher MAPP/organoclay

ratios resulted to better modulus and yield strength.

The toughness of TPO could be maintained at moderate

levels of MMT and MAPP. Kusmono et al. (2008) prepared

the blends of PA6 with PP. The use of maleated styrene-

ethylene-butylene-styrene (SEBS-g-MA) with nanoclay

resulted to higher ductility, impact strength, and thermal

stability. Bandyopadhyay and Ray (2010) studied the

dispersion of clay particles in poly[(butylene succinate)-

co-adipate]. SEM result showed dispersion of clay in

polymer. With an increase in clay loading, the dispersed

clay structure of nanocomposites changed from highly

delaminated to flocculated and finally to stacked interca-

lated. OMMT loading controlled the network structure of

the dispersed silicate layers, and 5 wt% of OMMT was the

threshold value for the formation of a strong flocculated

structure. Goodarzi et al. (2010) studied the morphologi-

cal behavior of modified montmorillonite (OMMT)-based

PP/EVA copolymer nanocomposites. With an increase in

the compatibilizer/OMMT weight ratio (C/O), the droplet

size (D n ) of EVA has a dual influence on clay interlayer

spacing (initially an increase then a decrease). The

highest clay interlayer spacing was obtained at a critical

EVA droplet size of 0.43 μ m, above which it decreased.

D n and char-yielding parameters decreased monotoni-

cally with higher activation energy, but OMMT inter-

layer spacing had a complex correlation with activation

energy. In a thermo-oxidative degradation process, the

char surface was smooth with many holes, but a rough

and spongy char surface was obtained under thermal

degradation in the absence of O 2 .

Su et  al. (2011) studied the effect of supercritical

(Sc) carbon dioxide on the mechanical properties of PP,

poly(ethylene-co-octene copolymer) (PEOc) reinforced

with clay particles. The use of Sc-CO 2 facilitated the

intercalation of the clay layers by the polymer chains and

become well exfoliated in the nanocomposites, leading to

a three-dimensional network structure. A higher impact

strength of PP without affecting stiffness and strength

was observed with the use of PEOc and clay. Sc-CO 2 was

more effective in improving the mechanical properties

of nanocomposites compared with MAPP. Dayma et  al.

(2013) studied the fracture properties of the PA6/PP blend

modified with maleic anhydride (PP-g-MA) and nanoclay.

Fourier transform infrared (FTIR) indicated tripartite

interactions among amide functionality, MA moiety, and

the hydroxyl group of nanocomposite. Essential work of

fracture (EWF) was increased by 35% with incorporation

of 2 wt% nanoclay followed by continuous reduction up

to 67% with 6 wt% nanoclay loading, whereas non-EWF

( β w p ) increased almost consistently up to 264% in the

entire composition range. Entezam et  al. (2013) studied

the blends of the nanoclay-filled PP/PET immiscible

blends. The localization of nanoclay in blends could be

detected by observing the changes in crystallization tem-

perature and crystallinity. Mechanical properties such as

tensile strength were affected by the localization of the

nanoclay in matrix phase only. Localization of nanoclay

particles in the matrix phase was more efficient in increas-

ing tensile modulus than in the disperse phase. Sedigheh

et  al. (2012) studied the morphology of the PP/ethylene-

octene copolymer (EOC)/clay nanocomposite by the addi-

tion of MAPP and maleic anhydride-grafted poly(EOC).

Clay with intercalated structure was obtained with EOC,

whereas the addition of MAPP resulted in the migration of

intercalated clay from EOC to PP and interface regions. A

higher impact strength of nanocomposites compared with

neat blends was reported.

3 Conclusions PPNC composites are widely used at present. PP and

clay are nonmiscible because of the difference in their

polarity; therefore, clay polarity needs to be changed to

organophilic for successful formation of composites. Dis-

persion of clay with PP can be enhanced using MAPP as

compatibilizer.

The extremely high surface-to-volume ratio of nano-

particles brings dramatic changes in their properties such

as mechanical (tensile strength, stiffness, and toughness),

barrier, heat resistance, flame retardancy, chemical resist-

ance, and dimensional stability. Good gas barrier property,

transparency, and long shelf life are important properties

for food applications. High-strength materials are useful

in structural applications such as windmill blades and

446      V. Kumar and A. Singh: Polymer composites

aircraft components. Silicon- and carbon-based compo-

sites are successfully used for making anodes for lithium

ion batteries. Lower solvent transmission through poly-

mers find applications in fuel tank and fuel-line compo-

nents. Some of the challenges such as optical issues and

dispersion difficulties with nanofillers need to be sorted

out for better utilization of these materials.

Received May 1, 2013; accepted July 23, 2013; previously published

online September 9, 2013

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448      V. Kumar and A. Singh: Polymer composites

Amandeep Singh is currently working on his MTech degree in the

Chemical Technology Department of Sant Longowal Institute of

Engineering and Technology, Longowal, Sangrur, Punjab, India. His

thesis is “ A Study on the Mechanical and Morphological Characteri-

zation of Coir Fiber Polyester Composites ” .

Vinay Kumar received his BTech degree from Harcourt Butler Tech-

nological Institute, Kanpur, India, and his PhD from Punjab Techni-

cal University, Jalandhar, Punjab, India. He is an assistant professor

in the Chemical Technology Department of Sant Longowal Institute

of Engineering and Technology, Longowal, Sangrur, Punjab, India.

He has an industrial experience of more than 10 years in plastic

processing industries. He coauthored Polymeric Systems and Applications and Advances in Polymeric Science and successfully

completed the research project “ Studies on Mechanical Proper-

ties of Rice Husk Based Polypropylene Composites ” funded by

AICTE New Delhi. He has research publications in various reputable

international journals and guided a number of MTech theses. He has

also designed the syllabi of different polymer courses at graduate

and postgraduate levels.