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: [email protected]
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.
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