ELASTOMER NANOCOMPOSITES

MADHUCHHANDA MAITI,† MITHUN BHATTACHARYA, ANIL K. BHOWMICK*

RUBBER TECHNOLOGY CENTRE, INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR-721302, INDIA

CONTENTS
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .385
II. Different Nanofillers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .386
A. Layered Silicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .386
B. Structure and Physical Characteristics of Montmorillonite . . . . . . .387
C. Synthetic Clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .388
D. Cation Exchange Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .389
E. Clay Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .389
F. Silica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .390
G. Carbon Based Nanofillers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .392
H. Layered Double Hydroxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .394
I. Other Nanofillers: Metals, Metal Oxides, Hydroxides and
Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .395
III. Commercial Nanofillers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .396
IV. Characterization of Nanofillers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .398
V. Preparation of Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .402
A. Solution Blending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .402
B. Latex Compounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .403
C. Melt Intercalation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .404
D. In-Situ Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .404
VI. Important Characterization Techniques Used for Polymer
Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .404
A. Microscopy and Diffraction Studies . . . . . . . . . . . . . . . . . . . . . . . .405
B. Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .411
VII. Structure and Properties of Different Elastomer Nanocomposites . . . . . .412
A. Natural Rubber (NR), Polyisoprene (IR) and Epoxidized
Natural Rubber (ENR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .413
B. Polybutadiene Rubber (BR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .417
C. Styrene Butadiene Rubber (SBR) . . . . . . . . . . . . . . . . . . . . . . . . . .419
D. Acrylonitrile-Butadiene Rubber (NBR) . . . . . . . . . . . . . . . . . . . . . .422
E. Ethylene Propylene Diene Methylene Rubber (EPDM) . . . . . . . . .424
F. Butyl Rubber (IIR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .426
G. Polyolefin Elastomer (POE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .428
H. Chloroprene Rubber (CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .429
I. Poly(Ethylene-Co-Vinylacetate) (EVA) . . . . . . . . . . . . . . . . . . . . . .429
J. Acrylates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .431
K. Silicone Rubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .437
L. Epichlorohydrin Rubber (CO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .438
M. Fluoroelastomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .439
N. Polyurethane (PU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .444
O. Thermoplastic Elastomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .445

* Corresponding author. Ph: (91-3222) 283180; Fax: (91-3222)-220312; email: anilkb@rtc.iitkgp.ernet.in

† Current address: Reliance Industries Ltd., VMD, Vadodara-391346, India
384
 ELASTOMER NANOCOMPOSITES 385

VIII. Comparison Between Properties of Conventional and Nanofiller

Filled Rubber Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .448
IX. Theories/Modeling in the Field of Rubber Nanocomposites . . . . . . . . . . .449
X. Health and Safety Aspects of Nanoparticles/ Nanocomposites . . . . . . . . .453
XI. Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .454
XII. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .455
XIII. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .456

ABSTRACT
Recently, elastomer - nanocomposites reinforced with low volume fraction of nanofillers have attracted great inter-
est due to their fascinating properties. The incorporation of nanofillers such as layered silicate clays, carbon nanotubes,
nanofibers, calcium carbonate, metal oxides or silica nanoparticles into elastomers improves significantly their mechan-
ical, thermal, dynamic mechanical, barrier properties, flame retardancy, etc. The properties of nanocomposites depend
greatly on the chemistry of polymer matrices, nature of nanofillers, and the method in which they are prepared. The uni-
form dispersion of nanofillers in elastomer matrices is a general prerequisite for achieving desired mechanical and phys-
ical characteristics. In this review article, current developments in the field of elastomer nanocomposites reinforced with
layered silicates, silica, carbon nanotubes, nanofibers and various other nanoparticles have been addressed. Attention has
been paid to the structure and properties of such high-performance nanocomposites, along with the theories and models
existing in this field.

I. INTRODUCTION
Nanotechnology is recognized as one of the most promising fields of research of 21st centu-
ry. The beginning of nanotechnology and nanoscience research can be traced back over 40 years.
However, it was in the past decade that the world witnessed bigger strides of this technology into
various disciplines. From chemistry to biology, from materials science to electrical engineering,
several tools have been created and expertise developed to usher nanotechnology out of the
research laboratories into the commercial market.
The term, "nanocomposite" refers to every type of materials having fillers in the nanometer
size range, at least in one dimension.1-16 More specifically, polymers that are reinforced with
rigid inorganic/organic particles, which have at least one dimension in the nanometer size-range
are termed as polymer nanocomposites. These organic-inorganic hybrid materials play important
roles as structural composites and represent some of the finest examples of optimized interfacial
interaction between the matrix and the filler particles via small-scale design. 17
Hybrid formation is an important and evolutionary route for the growth of a strong polymer-
filler interface. Increasing interest in hybrid formation of organic-inorganic materials stems from
the ability to control the nano-architecture of materials at a very early stage of preparation. These
can often be directed at a molecular level, almost a billionth of a meter in length. Depending on
the level of interaction between these organic-inorganic phases, hybrid materials can either pos-
sess weak interaction between these phases such as van der Waals, hydrogen bonding or electro-
static interaction18,19 or be of strong, chemically bonded (covalent or coordinate) types.20 Crucial
parameters in determining the effect of fillers on the properties of composites are filler size,
shape, aspect ratio and filler-matrix interactions.21-28
Nanofillers are necessarily nanoscopic and have a high specific surface area. The specific
surface area is one of the reasons why the nature of reinforcement is different in nanocomposites
and is manifested even at very low filler loadings (< 10wt%). In typical micro- and macro-com-
posites, properties are dictated by the bulk properties of both matrix and filler. This relationship
between the properties of the composite and the properties of the filler is what leads to the stiff-
ening and lower elongation. In the case of nanocomposites, the properties of the material are
more tied to the interface. The terms like "bound polymer," and "interphase" have been used to
describe the polymer at or near the interface. Interfacial structure is known to be different from
386 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

bulk structure, and in polymers filled with nanofillers possessing extremely high specific surface
areas, most of the polymer is present near the interface, in spite of the small weight fraction of
filler. If the interaction at the interface is a strong one, or if the structure of the interfacial poly-
mer is very different from the bulk, markedly different properties in the material as a whole can
be observed. These changes have a fundamentally different origin than those found in micro- and
macrocomposites, where the volume of the interphase is only a small fraction of the overall vol-
ume of the material. The particle size and the aspect ratio of the fillers make another difference
between conventional fillers and nanofillers.
With the plethora of nano-entities being introduced into rubber and rubber like materials the
need to collate this vast expanse of information arises. Their introduction has led to the emer-
gence of newer applications by virtue of the formation of functionally advanced materials.
Hitherto unforeseen processes, properties and eventually products are thus being pursued in lab-
oratories across the globe. In this review, we have compiled the current research on rubber
nanocomposites having a wide range of nanofillers. And unlike any previous effort, while span-
ning the broad gamut of nanofillers we have focused on the structure and properties of nanocom-
posites based on different elastomers.

II. DIFFERENT NANOFILLERS

The nanofillers used in polymer nanotechnology are usually, having different shapes and on
that basis can broadly be categorized into the following classes:
• Spherical/Cubical [e.g., nanosilica, polyhedral oligomeric silsesquioxanes (POSS),
nano CaCO3, metal oxides etc.]
• Rod/fibre (e.g., synthetic whiskers, carbon nanotubes, carbon nanofibers, boehmite,
sepiolite, nano CaCO3, etc.)
• Sheet/platelet (e.g., layered silicates such as smectite group clays, synthetic mica etc.).
The details about the nanofillers used in elastomers are discussed below.

A. LAYERED SILICATES

The silicates are the largest, the most interesting and the most complicated class of minerals
by far. Approximately 30% of all minerals are silicates and geologists estimate that 90% of the
Earth’s crust is made up of silicates.
The basic chemical unit of silicates is the (SiO44-) tetrahedron with a negative charge (-4).
They can form as single units, double units, chains, sheets, rings and framework structures.
The silicates are divided into the following subclasses, not by their chemistries, but by their
structures:29
• Nesosilicates (single tetrahedrons)
• Sorosilicates (double tetrahedrons)
• Inosilicates (single and double chains)
• Cyclosilicates (rings)
• Phyllosilicates (sheets)
• Tectosilicates (frameworks)
The layered silicates mostly belong to phyllosilicate subclass.

The Phyllosilicate Subclass (Sheets). — In this subclass, tetrahedrons are linked by shared
oxygens to other tetrahedrons in a two dimensional plane that produces a sheet-like structure.
The typical crystal habit of this subclass is flat, platy, book-like and display good basal cleavage.
Some members of this subclass have the sheets rolled into tubes that produce fibers as in asbestos
serpentine. This phyllosilicate subclass contains the clay group.
 ELASTOMER NANOCOMPOSITES 387

The Clay Group is consisting of four subgroups:

• Kaolinite
• Smectite
• Illite
• Chlorite

The Kaolinite Group. – This group has three members (kaolinite, dickite and nacrite) and a
formula of Al2Si2O5(OH)4. The different minerals are polymorphs, meaning that they have the
same chemistry but different structures. The general structure of the kaolinite group is composed
of silicate (s) sheets bonded to aluminum oxide/hydroxide layers called gibbsite (g) layers. The
silicate and gibbsite layers are tightly bonded together.

The Smectite Group. — This group is composed of several minerals including pyrophyllite,
talc, vermiculite, saponite, hectorite (H), bentonite, nontronite, beidellite, volkonskoite, sepiolite
(SP), stevensite, sauconite, sobockite, vinfordite, kenyaite and most importantly of them all
montmorillonite (MMT). They differ mostly in chemical content. The general formula is (Ca,
Na, H) (Al, Mg, Fe, Zn)2(Si, Al)4O10(OH)2 - xH2O, where x represents the variable amount of
water that members of this group could contain. The structure of this group is composed of sili-
cate layers sandwiching a gibbsite (or brucite) layer in between, in a silicate-gibbsite-silicate (s-
g-s) stacking sequence. The variable amounts of water molecules would lie between the s-g-s
sandwiches.

The Illite (or Clay-mica) Group. — The mineral illite is a significant rock-forming mineral
being a main component of shales and other argillaceous rocks. The general formula is (K,
H)Al2(Si, Al)4O10(OH)2 - xH2O, where x represents the variable amount of water that this group
could contain. The structure of this group is similar to the montmorillonite group with silicate
layers sandwiching a gibbsite-like layer in between, in an s-g-s stacking sequence.

The Chlorite Group. — This group is not always considered a part of the clays and is some-
times left alone as a separate group within the phyllosilicates. It is a relatively large group
although its members are not well known.
Till date smectite group clays are the most used nanofillers in elastomers. MMT is the most
common smectite clay.30,31 The structure and properties of MMT are discussed below.

B. STRUCTURE AND PROPERTIES OF MONTMORILLONITE -PHYSICAL CHARACTERISTICS

Many varieties of clay are aluminosilicates with a layered structure which consists of silica
(SiO44-) tetrahedral sheets bonded to alumina (AlO69-) octahedral ones. These sheets can be
arranged in a variety of ways; in smectite clays, a 2:1 ratio of the tetrahedral to the octahedral is
observed.
The structure of montmorillonite ((Na,Ca)0.33(Al, Mg)2(Si4O10)(OH)2 - nH2O) is derived
from the original pyrophyllite structure by partial substitution of the trivalent Al-cation in the
octahedral layer by the divalent Mg/ Fe-cation or that of Si-cation by Al in the tetrahedrdral layer.
Because of the difference in charge between the Al and Mg/Fe ions, the centre layer of these 2:1
silicates is negatively charged and the negative charge is balanced by group I or II metal ions
present between the 2 :1 sheets. Montmorillonite can absorb water between the charged layers
because of the weak binding and the large spacing and it is therefore a member of a group of
water-expandable clay minerals known as smectites or smectite clays. As clearly shown in Figure
1, in MMT, oxygen atoms from each alumina octahedral sheet also belong to the silica tetrahe-
dral ones, the three of them consisting of ~1 nm thin layer.
388 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

These layers are in turn linked together by van der Waals bonds and organized in stacks with
a regular gap between them called 'interlayer' or 'gallery'. Within the layers, isomorphic substi-
tution of Al3+ with Mg2+ or Fe2+ (or, substitution of Si4+ with Al3+) generates an excess of nega-
tive charge, the amount of which characterizes each clay type and is defined through the cation
exchange capacity (CEC), defined later. The CEC value for smectites depends on its mineral ori-
gin and is typically 65-150 meq/100g. In natural clays, ions such as Na+, Li+ or Ca2+ in their
hydrated form balance this excess negative charge; this means natural MMT is only compatible
with hydrophilic polymers. General characteristics of these materials include 20 layers of ~1 nm
thickness and lateral dimensions ranging from ~25 nm to ~5 µm.30

FIG. 1. — Structure of a typical MMT layer.

The mechanical properties of a single silicate layer are often assumed to be similar to mate-
rials like glass and mica, and elastic moduli around 170 GPa are frequently mentioned in the lit-
erature.32 These silicate layers allow for the retention of aspect ratios in excess of 100-1000 dur-
ing normal polymer processing, something that is exceedingly difficult to achieve with conven-
tional fillers. Additionally, such systems also benefit from the extremely large amount of inter-
face and interphase polymer produced due to full dispersion of nanometer thick silicate layers in
the polymer matrix.

C. SYNTHETIC CLAY

Undoubtedly natural montmorillonite constitutes the most commonly studied layered sili-
cate for producing clay based nanocomposites. But one of the major problems associated with
the use of natural clays is that there is fluctuation in purity and variation in composition from var-
ious sources. By synthesizing the clays in laboratory, the purity, the gallery spacing and surface
area can be controlled. Maiti and Bhowmick33 synthesized smectite group of clays namely, hec-
torite and montmorillonite. It was observed that clay formation was a function of the concentra-
tion of the constituent materials. For synthesis of montmorillonite, fresh magnesium hydroxide
[Mg(OH)2] was precipitated from magnesium acetate solution at room temperature. Then this
freshly prepared Mg(OH)2 was washed several times with water. It was then added wet to the
aluminum hydroxide [Al(OH)3] solution. Sodium chloride [NaCl] solution was also added to it.
This slurry was stirred for about 30 min before addition of silica sol [Ludox HS-30, Na+ stabi-
 ELASTOMER NANOCOMPOSITES 389

lized, 30% water dispersion]. Water was subsequently added to it to have a ratio of 80:20 of water
and the solid suspension. The pH was kept in between 9 and 10. This was then subjected to
hydrothermal crystallization at 325 °C under autogenous pressure for 2 h. The product was col-
lected, washed, and vacuum-dried. Synthetic clays showed larger d-spacing than the natural one.
The synthetic clays were also much purer than the natural one.33

D. CATION EXCHANGE CAPACITY

The cation exchange capacity (CEC) is one of the basic properties of clay minerals. It has
two origins. One origin is isomorphic substitution in the tetrahedral- and/or octahedral sheet of
the clay mineral layer. Substitution of aluminum by magnesium or of silicon by aluminum leads
to a negative net charge. This part of the CEC is considered to be constant since it is almost
insensitive to the pH of the system. The second origin is dissociation of aluminol groups on the
edges. Since the acidity of these groups is weak, the edge charges are pH dependent and the CEC
depends on the pH. At pH 7, about 20% of the CEC of smectites is located at the edges.34 Several
methods to determine the CEC have been developed.35 Presently, metal-organic complexes are
employed as exchange cations. The affinity of the clay minerals towards this type of cation is
high, so that complete exchange can be achieved in one single treatment step.36 An excess of the
complex is added to the clay dispersion and one has to only determine the remaining concentra-
tion after the exchange reaction. Cobalt hexamine, silver thiourea, copper bisethylenediamine or
copper triethylenetetramine can be used for this purpose.

E. CLAY MODIFICATION

In order to render MMT compatible with hydrophobic polymers, it is required to replace the
alkali ions with ω-amino acid hydrochloride salt,37 and organic surfactants, such as alkylammo-
nium and arylphosphonium ion.38-41 The surfactant provides a hydrophobic nature to the silicate
surface, which causes the layers to become organophilic and such clay is known as organoclay.
Several surface treatments can be applied to the clays in order to make them organophilic and
more likely to disperse them in the polymer matrix. Ray and Bhowmick modified montmoril-
lonite clay by treating with dimethyl sulfoxide and then subsequently replacing that with glu-
tamic acid, followed by the diffusion and polymerization of acrylate monomer to form in-situ
modified and polymerized organic-inorganic nanocomposite of polytrimethylol propane triacry-
late and montmorillonite.42 Sadhu and Bhowmick modified montmorillonite clays with various
amines, like stearyl, hexadecyl, dodecyl and decyl amine and subsequently utilized them to form
SBR-clay nanocomposites, which have been discussed in later sections.43
These surfactant molecules increase the layer distance and improve the compatibility with
the polymer.44 In order to enable each layer to be coated with the surfactant [e.g., primary, sec-
ondary, tertiary and quaternary alkyl ammonium cation], the layers should be accessible for the
surfactant molecules from the solution, and for this reason the clay layers need to swell to exfo-
liate in the solvent (usually water). Smectite clays are negatively charged and swell in water, and
can therefore be coated with a cationic surfactant in an aqueous suspension (as shown in Figure 2).
390 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 2. — Schematic showing clay modification.

The space between the silicate layers depends greatly on the length of the alkyl chain and
the ratio of cross-sectional area to available area per cation.45
Clays can also be modified with metal complexes such as Ni(II) bipyridyl or 1,10-phenan-
throline complexes to get increased gallery-distance.46 Alternatively, the clays may be forced
apart by in-situ polymerization, or even ion exchanged with reactive species of some sort in order
to enhance the polymerization rate in the interlayer regions and separate the layers better.
Another type of silicate modification targeted at improving polymer compatibility involves silane
treatment of exposed hydroxyls, located on the edge or the surface of the silicate layers, in order
to produce covalently bound organic functionalities.47-49
The dried organoclay can be used to produce nanocomposites by several methods, though
only a limited number of combinations of surfactant and polymers will result in a good disper-
sion.
There are some other novel modification techniques like modification of pristine clays or
organoclays with transition metal ions50 and with nanowires or nanotubes.51

F. SILICA

Nanosilica can be produced through sol-gel techniques. The sol-gel process begins with a
solution of silica alkoxide precursors [Si(OR)n] and water, where R is typically an alkyl group.
Hydrolysis and condensation of the alkoxide are the two fundamental steps to produce a network
(Figure 3) in the presence of an acidic or a basic catalyst. Silicon alkoxide (e.g. TEOS)52 is the
most commonly used precursor due to its mild reaction condition. Reports are available on the
use of silica obtained from silicic acid for modification of polymers.53-55
 ELASTOMER NANOCOMPOSITES 391

FIG. 3. — A model showing the silica network dispersed within a polymer matrix.

Nanosilica can be obtained in powder form. The TEM image of such particles is shown in
Figure 4. Surface treatment of nanosilica [as depicted in Scheme 1] can make it organophilic and
thus dispersion in elastomers can be enhanced.

FIG. 4. — TEM image of nanosilica.56

392 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

SCHEME 1. — Surface modification of nanosilica.56

G. CARBON BASED NANOFILLERS

The carbon-based nanofillers are mainly layered graphite, nanotube and nanofibers.
Graphite is an allotrope of carbon, the structure of which consists of graphene layers stacked
along the c-axis in a staggered array.57 Figure 5 shows the layered structure of graphite flakes.

FIG. 5. — 3D structure of graphene layers in graphite.58

When such a graphene sheet is rolled over we get the cylindrical segment of a single wall
carbon nanotube. A single wall carbon nanotube is a hexagonal network of carbon atoms rolled
up into a seamless, hollow cylinder, with each end capped with half of a fullerene molecule.59
Although similar in chemical composition to graphite, carbon nanotubes (CNT) are highly
isotropic, and it is this topology that distinguishes them from other carbon structures and gives
them their unique properties. There are many possibilities for rolling a slice of graphene into a
seamless cylinder (Figure 6), because when rolled into a nanotube, the hexagons may spiral
around the cylinder, giving rise to "chirality", a twist that determines whether the CNT behaves
like a metal or a semiconductor. The diameter, chirality and form of the nanotube determine its
properties.59
 ELASTOMER NANOCOMPOSITES 393

FIG. 6. — Rolling up of graphene sheet into a single wall carbon nanotube.

The discovery of multi-walled carbon nanotubes produced by the arc evaporation of graphite
in an atmosphere of helium by Iijima has attracted scientific and technological interest world-
wide.60
Carbon nanotubes can be classified into single-walled nanotubes (SWNT), multi-walled
nanotubes (MWNT) depending on the number of graphitic cylinders with which it is formed.
SWNT with a diameter of 1—2 nm consists of a single graphene layer wrapped into a cylindri-
cal shape, and hemispherical caps seal both ends of the tube. SWNT can be further divided into
three classes, i.e. armchair, zigzag and chiral depending on the arrangement of hexagons in their
structures (Figure 7).61 MWNT generally exists with diameter of 10-40 nm with length of few
micrometers. SWNT and MWNT can be synthesized by means of the arc discharge,62 laser abla-
tion63-66 and chemical vapor deposition (CVD) from hydrocarbons.67-69

FIG. 7. — (a) Different classes of SWNT;

(b) atomic force microscopy image of a chiral tube with a diameter of 1.3 nm.61

CNT prepared from the arc discharge, laser ablation and thermally activated CVD contain
impurities like amorphous carbon, graphite particles and metal catalysts. Therefore, purification
of CNT is needed prior to blending with polymers. CNT can be purified by oxidation, acid treat-
ment or combined oxidation and acid treatment.70-75 Ijima and coworkers established various
steps to purify SWNT, synthesized from metal catalyzed laser ablation.74,75 First step was to heat
394 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

the sample initially in air at 350 °C for 2 h in order to remove amorphous carbon. In the second
step, the remaining soot was soaked in 36% HCl for 1 day and centrifuged for the removal of
metal catalysts. In the last step, the sediment was washed with de-ionized water three times, dis-
persed in 0.2% benzalkonium chloride solution and filtered with PEFE membrane (expanded
polytetrafluroethylene, Gore-Tex Inc., Delaware). Liu et al. treated the laser ablated SWNT in
nitric acid or in a mixture of 3:1 sulfuric/hydrochloric acid to convert the SWNT from nearly
endless and highly tangled ropes into short and open-ended pipes.71 The nanotube caps are more
reactive, because of their high degree of curvature can readily react with a strong acid. Functional
groups such as carboxylic acid (—COOH) and hydroxyl groups (-OH) are bonded to the nan-
otubes at the open ends or the sidewall defect sites upon oxidative or acid treatments.71,76 This
implies that the CNT can be solubilized through chemical modification or functionalization.
Haddon et al. first used such carboxylic acid groups formed on SWNTs to interact with long-
chain aliphatic amine such as octadecyl amine [CH3(CH2)17NH2] via amide linkages.77-78 The
carboxylic acid moieties at the defect sites can be used to link polymeric or oligomeric functional
groups. This leads to an improvement in compatibility between the functional CNT and polymer
matrices of the nanocomposites. The solubilization of CNT via chemical functionalization is
considered as an effective way to achieve homogeneous dispersion of CNT in polymer matri-
ces.76-78
Vapor grown carbon nanofibers (VGCF) are another important member of this class of car-
bon based nanofillers. They possess the graphitic structure similar to that of CNTs, with typical
diameters of 50 -200 nm. The inner diameter is 30-90 nm and the length is in the range of 50-
100 μm, so that the aspect ratios are in the 100-500 range.79

H. LAYERED DOUBLE HYDROXIDE

In recent years, it has been found that layered double hydroxides (LDH), also known as
hydrotalcite-like compounds, have attracted great attention, because of their layered structure
and high anion-exchange capacity, which enables various technical applications.80-85 Layered
double hydroxides (LDHs) belong to a general class called anionic clay minerals. They can be
of both synthetic and natural origin. The most commonly known naturally occurring LDH clay
is hydrotalcite having chemical formula [Mg6Al2(OH)16]CO3.4H2O. The general chemical for-
mula of LDHs is written as [MII xMIII 1-x(OH)2]x+(An-)x/n.yH2O, where MII is a divalent metal ion,
such as Mg2+, Ca2+, Zn2+, etc, MIII is a trivalent metal ion, such as Al3+, Cr3+, Fe3+, Co3+, etc.,
and An- is an anion, such as Cl-, CO32-, NO3-, etc. The anions occupy the interlayer region (Figure
8). Though a wide range of values of x is claimed to provide LDH structure, the pure phase of
LDHs is usually obtained for a limited range as 0.2 < x <0.33.85 Layered double hydroxides and
their derivatives are inorganic materials with a positive layer charge in which the interlayer
anions can be replaced by ion-exchange processes.
 ELASTOMER NANOCOMPOSITES 395

FIG. 8. — Structure of a typical LDH layer.86

Owing to its high anion- exchange capacity, LDHs have found many potential applications,
including those in pharmaceutical, catalyst supports, inorganic fillers, etc. Since, the hydroxide
layers of all LDH clays are positively charged, the chemicals used for modification universally
contain negatively charged functionalities. The primary objective of organic modification is to
enlarge the interlayer distance of LDH materials so that intercalation of large species, like poly-
mer chains and chain segments becomes feasible. Organic anionic surfactants having at least one
anionic end group and a long hydrophobic tail are the most suitable materials for this purpose.
Due to these hydrophobic tails, the surface energy of the modified LDHs is reduced significant-
ly compared to the unmodified LDHs. As a result, the thermodynamic compatibility of LDH with
polymeric materials is improved facilitating the dispersion of LDH particles during nanocom-
posite preparation. Principally, the methods used for the synthesis of LDH materials are also suit-
able for their modification using organic surfactants. For example, methods like co-precipitation
in aqueous solution of organic surfactants, ion exchange methods, etc. are widely reported in lit-
erature.87,88 Besides all these methods, another method called 'regeneration method' is also wide-
ly used for the modification of LDHs. This method is based on the so called 'memory effect'
shown by the carbonate containing LDH materials. When such LDH is heated above 450 °C for
several hours, it is converted into an amorphous mixed oxide, which after dispersion in an aque-
ous solution containing suitable anionic species and subsequent ageing regenerates the original
LDH structure (as if the materials remember its original structure).89 This regeneration is also
possible in presence of large anionic species, like many organic anionic surfactants.

I. OTHER NANOFILLERS: METALS, METAL OXIDES, HYDROXIDES AND CARBONATES

Metal nanoparticles embedded in host polymer matrices have become the focus of increas-
ing attention, since the properties of these materials can be tailored by altering the metal parti-
cles, their size and shape, distributions or their relative concentrations. These novel hybrid mate-
rials can show combined properties, such as strength, toughness, elasticity, electrical conductiv-
ity and improved electro-optic performance.90-99
Recently, several metal oxides apart from silica have been investigated and reported for rub-
ber-based nanocomposites. Such important and commercially meaningful materials used in rub-
bers are zinc oxide, magnesium hydroxide, calcium carbonate, zirconate, iron oxides, etc. To
form zinc oxide (ZnO) nano particles, Zn(NO3)2. 6H2O and (NH4)2CO3 were dissolved in dis-
396 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

tilled water to form 1.0M solutions.100 Zn(NO3)2 solution was gradually dropped into the vigor-
ously stirred (NH4)2CO3 solution, with a molar ratio of 1:2. A white precipitate was formed when
the two solutions were mixed with each other, but it dissolved with stirring. Slowly a stable state
of supersaturation was achieved because of the high concentration of Zn2+ ions in the mixed solu-
tion. The solid was collected by filtration and repeatedly rinsed with ethanol and then dried at
100 °C for 12 h. ZnO nanoparticles were obtained after calcination at 280 °C for 2 h.100 The pro-
cedure was very similar to that reported by Wang and Gao.101 Different elastomer-nano ZnO
hybrid systems have been reported by several researchers.100-105
The synthesis of magnesium hydroxide (MH) nanoparticles with special morphologies has
recently attracted much attention because of the expectation of novel properties and applications
in electronics, catalysis, ceramics, nanostructured composites or halogen free flame- retar-
dants.106-110 For example, MH nanorods could be used as precursors for the synthesis of magne-
sium oxide MgO nanorods,111 which are expected to have novel mechanical, catalytic and elec-
tronic properties due to their extremely small size, large anisotropy and perfect crystallinity.112
MH nano-needles and nano-lamellas could be good candidates for functional polymeric com-
posites and fiber hybrid materials as reinforcing agents or halogen-free flame-retardants.113,114
Nano-CaCO3 is the cheapest commercially available nanofiller, and has the additional
advantages of a low aspect ratio and a large surface area.115 Several researchers have prepared
CaCO3 nanoparticles116-119 and studied the mechanical properties of the reinforced rubber com-
posites. Micron-sized calcium carbonate has been historically used to lower the cost of relative-
ly expensive polymer resins. It has very limited effects on property improvement due to the poor
particle-polymer interaction. However, due to the larger interfacial area in nano-sized
CaCO3/polymer, its properties are expected to be better than the micron-sized CaCO3/polymer
composites. The nano-sized precipitated calcium carbonate is usually coated with stearic acid to
increase dispersion and compatibility with the polymer matrix. The calcium carbonate particu-
lates can be rhombohedral, which are cubic in shape or scalenohedral which are cigar-like, with
an average primary particle size of 40-70 nm, narrow particle size distribution and BET surface
area >40 m2/g. Besides this, ortho-rhombic, needle like structure of Aragonite is also there.120-122
The sol-gel transition method has been used to generate a wide variety of synthetic nano-
fillers, including metal, metal oxides (e.g. Cr3O8, V2O5 etc.), layered chlorides (e.g. FeOCl),
chalcogenides (e.g. MoS2), functional or structural nano-fillers, and others.123 Polymer interca-
lated layered zirconium phosphates have been produced.124,125 More recently, rod-like synthetic,
unmodified boehmite (g-Al2O3) was dispersed in caprolactam.126
Recent development of rubber nanocomposites by other nanofillers include piezo-rubber
application by incorporating Pb-Zirconate by Tandon et al.,127 Fe containing silicone rubber by
Yurkov et al.,128 crab-shell whisker reinforced natural rubber nanocomposites by Nair and
Durfreshe129 etc.

III. COMMERCIAL NANOFILLERS

The partial list of the different commercially available nanofillers, their type, classification,
trade name and their suppliers is given in Table I.
 ELASTOMER NANOCOMPOSITES 397

TABLE I
PARTIAL LIST OF COMMERCIAL NANOFILLERS
Company Type of Nanofiller/Specs. Trade Name
Rockwood Specialties, Inc.; Southern Natural and organophillic Cloisite, Nanofil
Clay Products, www.nanoclay.com MMT clay
Hectorite clay Optigel SH
Nanocor, www.nanocor.com Natural and organophillic Nanomers
MMT clay
TNO, www.tno.nl Natural and organophillic Planomers
MMT clay
Kunimine Industries Co., Ltd. MMT clay: natural and Kunipia F/T/D
Tokyo, Japan, Matsudo@kunimine.co.jp organo modified Na-Saponite Sumectone-SA
Tolsa , Tolsa S.A., Madrid
Spain, www.tolsa.com Organo modified Sepiolite clay Pangel
NL Industries; Baroid Division, Muscovite-type mica-MMT Barasym
idp@baroid.com clay SMM-100
CBC Co. Ltd.erstwhile UNICOOP, Hectorite-type clay Somasif,
wakisaka@cbc.co.jp Lucentite
Sud-Chemie AG, Synthetic aluminum- Hydrotalcite
www.sud-chemie.com magnesium-hydroxycarbonate
(LDH)
Sasol Germany GmbH, Marl, Synthetic magnesium- Pural MG30,
Germany, marlotherm@de.sasol.com aluminum type LDH MG50, MG70
Akzo-Nobel, http://www.akzonobel- Synthetic magnesium- Perkalite
polymerchemicals.com aluminum type LDH
BuckyUSA, Alberene Dr. Houston Fullerenes and nanotubes BU-600 series
TX, USA, http://buckyusa.com/index.htm and BU-200 series
CarboLex, Inc., Parkway Single-walled carbon AP-Grade
Broomall, PA, USA, nanotubes (SWNT) Nanotubes
http://carbolex.com/
Pyrograph Products, Cedarville, Ohio, USA Nanographite, carbon Black Icetm and
http://www.apsci.com/ppi-about.html nanofiber Pyrograph I and III
Polytech & Net GmbH, Schwalbach, Carbon nanotubes -
Germany, http://www.polytech-net.de/content/
Nanostructured & Amorphous Nanoscale metal oxides, -
Materials, Inc., Houston, Texas USA, nitrides, carbides, diamond,
http://www.nanoamor.com/ carbon nanotubes
NanoMetal, GunPo, South Korea, Nanometal powders -
http://myhome.naver.com/nanometal/ and nanofibers
Nano-Vision Tech, RM No.305, Defense Nanomaterials such as -
Technology Venture Center, Seoul, particles, fibers and
South Korea, carbon nanotubes
http://www.nanovistech.com/main_nano.asp
language=EN
Electrovac AG Carbon nanofibers ENF and HTF
Aufeldgasse, Klosterneuburg grades
Austria, http://www.electrovac.com/
Catalytic Materials, LLC, Pittsboro, Carbon nanotubes, Platelet -
North Carolina, USA, Graphite Nanofibers and
http://www.catalyticmaterials.com/ nanochips
Nano Technology Inc., KAERI Daejeon, Metal/Ceramic Nano Powder: -
South Korea, www.nanocompound.com Al, Cu, Fe, Ag, Sn, W, Zn,
Cu-Ni Alloy, CuO, ZnO,
SnO2
398 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

Nano Fiber: Al2O3, Fe2O3

Inframat® Advanced MaterialsTM Nano oxides (eg., ZnO, TiO2 -
LLC, Farmington, CT, USA etc.), nano carbides and
http://www.advancedmaterials.us/nanomat.htm nitrides, nano metal
powders
NanoMaterials Technology Pte Ltd Nano CaCO3 Nano-sized
Singapore, http://www.nanomt.com/ precipitated calcium
NPCC
Solvay Advanced Functional Minerals, Via Precipitated Nano SOCAL and
Varesina Angera (VA), Italy Calcium Carbonate WINNOFIL
http://www.solvaypcc.com/
MicrotechNano, LLC, Indianapolis, USA Carbon nanotubes, L/S/D/W/T/M
http://www.microtechnano.com/ Nanometallic particles: -WNT
Al2O3, Fe/Ni,
Nanowires
Filigree Nanotech Silver nanowire SNW series and
North Carolina, USA and nanocube SNC series
http://www.filigreenanotech.com

IV. CHARACTERIZATION OF NANOFILLERS

X-Ray Diffraction (XRD) — X-ray diffraction (XRD) is commonly used for the characteri-
zation of the layered type of nanofillers like nanoclays, LDH, nanographite and other crystalline
nanomaterials (eg., nano ZnO, etc.).
The characteristic peak of (001) plane of MMT, H and SP is at 7.61°, 5.59° and 7.18°,
respectively. The d-spacing of layered silicates can be calculated using Bragg's law. The X-ray
diffractograms of various unmodified and modified montmorillonite, hectorite and sepiolite are
shown in Figure 9.130 After modification with organic amines, the d-spacing increases (Figure 9).

FIG. 9. - XRD pattern of different natural and modified clays used in rubber nanocomposites.130

XRD of MgAl-LDH as a pure hydrotalcite and organically modified LDH is depicted in

Figure 10a-b. The basal diffraction peak is the (003) diffraction peak which corresponds to the
basal spacing of 0.77 nm.131 It shows the basal spacing for the modified LDH is 2.56 nm from
the diffraction peak at 2θ = 3.45°.
 ELASTOMER NANOCOMPOSITES 399

FIG. 10. — XRD pattern of [a] pure LDH; [b] organically modified LDH.

Electron Microscopy. — Electron microscopy is another effective tool for characterizing

nanofillers. Both scanning electron microscopy (SEM) [particularly recent generation SEMs like
Field Emission SEM] and transmission electron microscopy (TEM) are extensively used these
days for this purpose.
The transmission electron micrographs of natural montmorillonites132 and sepiolite133 are
illustrated in Figure 11a and b, respectively. Figure 11a clearly depicts the layered platelet struc-
ture of the montmorillonitic clay, which is significantly different from the unexpandable layered
ribbon type bird's nest structure of fibrous sepiolite. Unlike smectites, which have a layered
structure, sepiolite has interstratified intergrowths. It can thus be regarded as a hybrid structure
between layer- and ribbon- structures. The presence of longitudinal channels and the lath-like
structure makes larger surface area available resulting in significant improvement of properties
in its nanocomposites.

FIG. 11. — TEM images of (a) natural montmorillonites; (b) sepiolite.

400 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

The scanning electron micrographs of LDH are illustrated in Figure 12a-b.131

FIG. 12. — SEM images of (a) pure Mg-Al LDH; (b) modified-LDH.

Figure 13a shows the transmission electron micrograph of the synthesized nano ZnO with
average particle diameter of 50 nm.100 Figure 13b illustrates the representative TEM of synthet-
ic montmorillonite. The particles are mainly in the form of cluster of almost rounded particles
with sizes in the nanometer range (~50nm), which has similarity with mechanically treated nat-
ural montmorillonite.33,134,135

FIG. 13. — TEM photomicrograph of (a) nano ZnO; (b) synthetic montmorillonite.

Figure 14a shows the transmission electron micrograph of commercially available vapor
grown carbon nanofiber. They have diameter in the range of 77± 12nm.136 Figure 14b represents
commercial multiwall nanotube having 27± 4nm diameter.137
 ELASTOMER NANOCOMPOSITES 401

FIG. 14. — TEM photomicrograph of commercially available

(a) Vapor grown carbon nanofiber; (b) multiwall nanotube.

Infrared Spectroscopy. — Figure 15 shows the IR spectra of different nanoclays. In the stud-
ies of clay minerals, the peaks due to structural OH and Si-O groups play an important role in
the differentiation of clay minerals from each other.138 The IR spectra can show the difference in
stacking the sheets as well as in the occupancy of the octahedral and tetrahedral sites. Mainly two
regions show characteristics of clays—- (i) the -OH stretching region in between 3400- 3700 cm-
1 and (ii) the region below 1200 cm-1. The -OH stretching band varies with the nature of the octa-

hedral atom to which the -OH group is attached. The hectorite, where -OH is attached to Mg,
shows a single stretching band ~ 3680 cm-1.138 Figure 15 shows only one broad complex stretch-
ing band ~1012 cm-1 for Si-O stretching, characteristic of smectites.

FIG. 15. — IR of different smectite clays.

402 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

Surface Area. — BET surface area of different nanoparticles is tabulated in Table II.33,139-148
The particle size and surface area of natural and expanded graphite were measured using a
Malvern-3601 (UK) particle size analyzer. It is observed that natural graphite has particle size of
67μm, and corresponding surface area of 0.15m2/cc, while expanded graphite is comprised of much
smaller particles of 22μm with almost double the surface area of their natural counterparts.149

TABLE II
BET SURFACE AREA OF DIFFERENT NANOPARTICLES
Nanoparticle BET surface area, (m2/g)
Natural hectorite 71.0
Synthetic hectorite 176
Laponite 316
Natural montmorillonite 40
Synthetic montmorillonite 198
Nano ZnO 35
Nano CaCO3 35
Carbon nanotube:
SWNT 948
MWNT 178
Carbon nanofiber 42
Nano silica 200

V. PREPARATION OF NANOCOMPOSITES
The reinforcement of rubber requires rigid entities, such as carbon black, clays, silicates, cal-
cium carbonate, zinc oxide, magnesium hydroxide and metal oxides, and this important phe-
nomena has been discussed at length by various authors.150-152 Thus, inclusion of these
nanofillers, or reinforcement aids to rubber formulations results in optimization of properties to
meet given service application or sets of performance parameters.153-158
Such elastomer nanocomposites are currently prepared in the following ways:
• Solution blending
• Latex compounding
• Melt intercalation
• In-situ polymerization

A. SOLUTION BLENDING

In this method, the elastomer is solubilized in a proper solvent and then the filler dispersion
is added to it. In solution, the elastomer chains are well separated and can easily enter inside the
layers of the layered nanofillers or can interact with the particulate nanofillers. After the
nanofillers get dispersed, the solvent is evaporated usually under vacuum. The curatives may be
added before solvent removal,159 but they are usually compounded with the intercalated materi-
al after partial or complete solvent removal160-162 and then vulcanized at a specific temperature.
Most of the elastomer-nanocomposites eg., natural rubber (NR),163-166 epoxidized natural
rubber (ENR),167-168 polybutadiene rubber (BR),169 styrene-butadiene (SBR),162 ethylene propy-
lene diene rubber (EPDM),131 butyl rubber (IIR),170 brominated poly(isobutylene-co-p-methyl-
styrene) (BIMS),171 fluoroelastomer (FKM),172 poly(ethylene-co-vinylacetate) (EVA),137,159
acrylonitrile butadiene rubber (NBR),162,173 epichlorohydrin,174 and chloroprene (CR)175 have
been synthesized by this method. Properties of some of the rubbers prepared by solution blend-
 ELASTOMER NANOCOMPOSITES 403

ing are discussed in later sections.

Carbon based nanofillers too have been dispersed in the above mentioned mode of solution
blending, although often such a mixing process is preceded by certain preprocessing stage, for
instance 1) dispersion of individual nanofillers by deagglomeration, 2) removal of non-nanotube
material and 3) functionalization by chemical modification. Since the preprocessing techniques
involve the nanofillers only and hence can be applied to either plastics or rubbers.

1. Dispersion of Individual Nanotubes by Deagglomeration. — The most common methods

for deagglomeration are ultrasonicating a CNT solution176,177 or ball-milling for breaking up the
agglomerates in VGCFs178 and in CNTs.179 Electrostatic plasma treatment is also used to sepa-
rate CNTs from the larger agglomerated particle mixture of other CNTs and impurities.180

2. Purification to Eliminate Non-Nanotube Material.181-188— Amorphous carbon,

fullerenes, nanocrystalline graphites, and transition metal catalysts are the common contaminants
of carbon nanotube.183 Thermal annealing in air or oxygen for selective etching of amorphous
carbons removes the deleterious carbonaceous matter, while acid treatment can eliminate cata-
lyst residues.184 Mechanical techniques like centrifugal separation, size exclusion chromatogra-
phy and microfiltration maybe applied as well.185-188

3. Chemical Functionalization for Improving Nanotube/ Matrix Interactions for

Processability and Property Enhancement. — Several approaches to functionalization have been
developed, including defect functionalization; covalent functionalization of the sidewalls; and
noncovalent exohedral functionalization with polymers or surfactants as supramolecular
adducts.189-194 Yet another possibility is to expose the nanotube composite to gamma radiation195
or plasma196 for altering the chemistry at the interface for property enhancement. Bubert et al.196
modified the nanotubes by means of polar groups generation on the surface.
To achieve load transfer across the CNT-matrix interface good interfacial bonding is
required which depends strongly on the ability to disperse the CNTs individually and uniformly
throughout the matrix, without any detrimental effect on their aspect ratio.197-199
Solution-based methods provide an advantage through low viscosities, which facilitate mix-
ing and dispersion of the CNTs. There are, however, limited examples of nanotube or nanofiber
incorporation in rubber matrices. Solution mixing of MWNT in NR,200-202 SBR,201,203 methyl
vinyl silicone,204 MWNT137 and expanded graphite205 filled EVA have been reported. Frogley et
al. discussed the ultrasonication and solution mixing of SWNT and VGCF in RTV silicone rub-
ber.206 Isayev has patented an ultrasound assisted continuous process in this regard.207 Silicone
rubber nanocomposites containing nano calcium carbonate,208 graphite nanosheets,209 and mag-
nesium ferrite210 have also been reported.

B. LATEX COMPOUNDING

Most of the elastomers are available in the form of latex, which is nothing but an aqueous
dispersion of elastomer particles in the submicron-micron range. Mostly layered silicate
nanocomposites are made by this method. In this method the host medium is water. To the elas-
tomer latex, pristine clay can be added directly or in its aqueous dispersion (slurry). The clays
are strong hydrophilic and adsorb water molecules which is associated with an expansion of their
intergallery spacing. Thus, hydration decreases the attractive forces between the silicate layers
making easier their exfoliation under stirring. After mixing, they are coprecipitated (coagulation)
and dried. In this case, the nanocomposite remains unvulcanized. On the other way, suitable cura-
tives, which can be dispersed in water, may also be mixed with the clay containing elastomer
latex. After drying the nanocomposites can be cured at a specific temperature.
404 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

Nanocomposites from NR,211 SBR,212-215 CR,216 carboxylated styrene-butadiene rubber

(XSBR),217 carboxylated acrylonitrile-butadiene rubber (XNBR),218 NBR,219 polyurethane rub-
ber (PU)220 have been prepared by this route. There are also some patents on this method.221,222
Nanocomposites having carbon nanotubes have been prepared from NR.223 It has also been
applied by Gauthier et al.224 for dispersing VGCNF in SBR.
Latex compounding has been successfully applied for dispersing nano calcium carbonate in
NR latex,225 while nanofibrous biomolecules for instance chitin 226 and cellulose227,228 have also
been incorporated by this technique in NR.

C. MELT INTERCALATION

From industrial stand point, the most economic mixing and environmental friendly tech-
nique used for preparing elastomer/organoclay nanocomposites is by far the melt compounding.
This involves equipment like internal mixers and open two-roll mills. The intercalation/exfolia-
tion phenomena are sometimes governed by the modification of elastomers and also the chem-
istry involved during compounding and curing in the case of elastomer-clay nanocomposites.
Mixing temperature and shear rate also influence the intercalation/exfoliation phenome-
na.130,136,229-233
There are substantial studies on ENR and NR.234-239 Schon and Gronski investigated the
reinforcement of SBR by silica and organoclay as nanofillers.240 Clay nanocomposites based on
NBR241-244 and EPDM245-247 have also been reported in the literature.
Melt mixing of MWNT has been carried out in NR,248 while Bhattacharya et al. have inves-
tigated the effect of different dispersion techniques in melt mixing of VGCNF in SBR130 and
NR.136
Preparation of NBR/expanded graphite nanocomposites by melt mixing has been studied by
Liu et al.249 There is a patent issued in this regard, as well.250 Nano-calcium carbonate compos-
ites too have been so derived in NR251 and SBR.252,253 Melt mixing is also the preferred mode of
incorporation of oxides like nano titanium dioxide,254 nano zinc oxide.255
Other miscellaneous fillers, for instance calcium sulphate256 and zinc dimethylacrylate257
too have been studied by melt mixing.

D. IN-SITU POLYMERIZATION

Monomers are added to the fillers and allowed to enter into the galleries for layered
nanofillers or mix with the fillers in a proper solvent medium. Then they are polymerized using
some initiator to get the in-situ nanocomposite. This method requires a certain time period,
which depends on the polarity of monomer, surface treatment of the filler and swelling temper-
ature, after which the reaction is initiated. There are a few elastomer-clay nanocomposites pre-
pared by this way.258-259
There are also some silica nanocomposites prepared by this way. In in-situ generated
hybrids, the organic and the inorganic components are allowed to grow simultaneously. The
monomers like acrylates and methacrylates or their derivatives are mostly used as the organic
components.258-261
Nanocomposites based on multiblock polyester elastomers (PEE) and carbon nanotubes
(CNT) have also been prepared by this method.262

VI. IMPORTANT CHARACTERIZATION TECHNIQUES

USED FOR POLYMER NANOCOMPOSITE
For appropriate structure-property correlation of nanocomposites, the knowledge of the state
and extent of nanofiller dispersion in the matrix is of paramount importance. Numerous methods
 ELASTOMER NANOCOMPOSITES 405

have been reported in the literature in this regard, for instance, X-ray diffraction — wide angle
X-ray scattering (WAXD),263,264 small angle X-ray scattering (SAXS),265-267 ultra small angle X-
ray scattering(USAXS),268 small angle neutron scattering (SANS),269,270 electron microscopy —
scanning electron microscopy (SEM), transmission electron microscopy (TEM),264,271 atomic
force microscopy (AFM),272,273 high resolution TEM (HRTEM), scanning TEM (STEM), and
electron energy loss spectroscopy (EELS) techniques,274 solid state nuclear magnetic resonance
(SSNMR),275-278 electron paramagnetic resonance (EPR),279,280 spectroscopy [UV/Vis/NIR,
FTIR,281 Raman,137 Dielectric,282,283 small angle light spectroscopy (SALS).284

A. MICROSCOPY AND DIFFRACTION STUDIES WAXD AND TEM

Amongst all those listed above, the two methods those have often been used to determine
the structure of nanocomposites are WAXD and TEM. For example, fluoroelastomer vulcan-
izates with 4 phr MMT (FNA4-V) shows a small hump at ~3.8°, whereas vulcanizates contain-
ing the same amount of modified clay (F20A4-V), Cloisite 20A, exhibits a small sharp peak at
~ 4° in the X-ray diffractogram (Figure 16).285 It indicates that the clays are mostly exfoliated in
FNA4-V. In F20A4-V, the (001) peak of MMT has shifted to lower 2θ values, with increasing d-
spacings. It reflects that the clay layers are intercalated in F20A4-V. But in the case of higher
loadings of MMT, FNA8-V and FNA16-V, there are two sharp peaks at ~6.8° and 9.6°. These
may be due to (001) and (110, 020) planes of stacked montmorillonite clay. This indicates that
the clay platelets are mostly stacked in these two samples.

FIG. 16. — XRD of different fluoroelastomer nanocomposites.

Most often only the (001) plane has been discussed while explaining intercalation into clay
galleries using X-Ray diffractograms. However, Galimberti et al. established the utilization of
higher order peaks to further support such observations.286
TEM micrographs of SBR-Cloisite 15A rubber nanocomposites are illustrated in Figure
17a-b.130 Figure 17a shows the distribution of small clusters quite homogeneously over the area
of interest. The higher magnification picture (Figure 17b) presents a better insight into the
nanocomposite morphology. Image analysis reveals that inter-particle distance is 208±119 nm
amongst the well dispersed stacks of thickness 35±3 nm, containing 8-10 clay platelets. Figure
406 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

17b also exhibits the presence of few isolated clay platelets, indicating partial exfoliation. This
illustrates the attainment of a partially exfoliated/intercalated state, with good dispersion. The
benefits of such morphology are experienced in terms of the extraordinary enhancement of
mechanical and dynamic mechanical properties.

FIG. 17. — TEM micrographs of SBR-Cloisite 15A rubber nanocomposites at (a) low and (b) high magnification.

In the case of clay or any other structurally layered inclusion containing nanocomposite,
monitoring the position, shape, and intensity of the basal reflections emanating from those lay-
ers elucidates the structure, namely, intercalated or exfoliated. Although WAXD can offer a con-
venient and often practiced method to determine the interlayer spacing, it cannot be considered
all-conclusive. The absence of Bragg diffraction peaks alone cannot be used to determine the for-
mation of an exfoliated structure; doing so can lead to false interpretations of the extent of exfo-
liation. Several factors such as clay dilution, peak broadening and preferred orientation make
XRD characterization of polymer nanocomposites susceptible to errors. To supplement the defi-
ciencies of WAXD, TEM can be used.264,271 XRD data are averaged overall the regions of the
specimen, while TEM can provide a qualitative understanding of the internal structure, spatial
distribution of the various phases and hence the morphology of the nanocomposites. However, it
must be noted that TEM is time consuming and gives information on selected regions of the sam-
ple, whereas low-angle peaks in WAXD allow quantification of changes in layer spacing.

SAXS. — SAXS presents itself as significant tool when layer spacings exceed 6—7 nm in
intercalated nanocomposites or when the layers become relatively disordered in exfoliated
nanocomposites.
The effects of nanoclay on the order structure of SEBS have been studied by Ganguly et
al.287 by comparing the intensity vs. scattering vector plots by small angle X-ray scattering
(SAXS)(Figure 18a) for neat SEBS and its nanocomposites. All the samples show at least two-
order scattering with the peak position ratio of 1 : 2, indicating the layered (lamellar) structures
(Figure 18a). With nanoclay loading, the corresponding lengths calculated from scattering vec-
tor positions (q, nm-1), for both the 1st and the 2nd order peaks, are found to increase. Among
these the incorporation of 2 pbw (parts per 100 parts per rubber by weight) loading of Cloisite
20A shows the maximum increase, with 4 pbw depicting almost similar effect as shown in the
Lorentz corrected SAXS profiles in Figure 18a-b. In order to further confirm the effects of nan-
oclays on SEBS, 2-dimensional SAXS studies clearly detect distinct pattern at 2pbw of Cloisite
20A loading. Isotropic circular rings are observed in the 2-d SAXS pattern for the as-cast sam-
ple films. These rings were ascribed to diffraction resulting from one-dimensionally alternating
 ELASTOMER NANOCOMPOSITES 407

lamellar microdomains and the ratio of q values for the 1st and 2nd diffraction rings can rela-
tively be assigned to 1 : 2. After 4 pbw loading of Cloisite 20A, the patterns become more and
more diffused and corroborates well with SAXS profile (Figure 18b).

FIG. 18a-b. — Effect of nanoclay loading on neat SEBS: (a) Lorentz —corrected SAXS profiles
(vertically shifted for better clarity) showing effect of nanoclay; and (b)lengths corresponding
to 1st and 2nd order scattering vector position along with their 2-dimensional SAXS patterns
for each sample (indicated at arrow head) for clay loaded nanocomposites.

In recent times, simultaneous SAXS and WAXD studies yielded quantitative characteriza-
tion of nanostructure and crystallite structure in nylon-6 based nanocomposites.288

SANS. — The SANS technique, combined with contrast variation, is able to highlight the
scattering from different components in the system and is, therefore, the most direct technique
for probing the size, shape, and conformation of an interfacial polymer layer on a colloidal par-
ticle. When the scattering length density of a particle (ρp) is equal to the scattering length densi-
ty of the solvent (ρsolv) it is dispersed in, the particle is said to be "contrast matched" and is essen-
tially "invisible" to the neutron beam. In the study of adsorbed polymer layers, this technique can
be used to isolate the signal of adsorbed polymer from the total scattering. By (partial) deutera-
tion of, for example, the solvent, the contrast between the system components can be varied. As
a result, neutron scattering experiments can reveal information not available from X-ray scatter-
ing which has been used more extensively. In comparison with techniques such as infra-red or
nuclear magnetic spectroscopy which study materials on the atomic level, neutron scattering
looks at a larger scale and can be used to study, for example, the effect of clay on the conforma-
tion of polymer chains.269,270

AFM. —The AFM phase images provide the size and dispersion of nanofillers in the rubber
matrix. The AFM images of the neat fluoroelastomer, the unmodified and the modified clay
loaded samples (F, FNA4, F20A4) are illustrated in Figure 19a-c.272
408 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG.19. — AFM phase image of (a) F (b) FNA4 (c) F20A4.

In the case of the clay-filled samples, some distinct white bright features are observed,
which are absent in the unfilled sample. This suggests that the filler appears as white bright fea-
tures in the brown rubber matrix. In the tapping mode, the measurement of the difference
between the phase angle of the excitation signal and the phase angle of the cantilever response
is used to map compositional variations such as stiffness, hardness and viscoelasticity on the
sample surface. The variation in the image contrast of the neat rubber and the filled systems can
be related to the sample modulus as follows.289 The phase image can provide a stiffness varia-
tion in the sample, which is expressed by the following equation:

Q Q
Δφ 0 ≈ S ⎛ ⎞ = ε a E ∗ ⎛ ⎞ (1)
⎝ k⎠ ⎝ k⎠

where, Δφ0 is the phase angle shift between free and interacting cantilevers; S is the stiffness of
the material; Q is the quality factor, which is a measure of viscous damping of the cantilever; k
is the spring constant of the cantilever; ε is a constant; α is the radius of the contact area between
tip and the surface; and E* is the effective modulus of the material. <S> and <a> are time-aver-
aged values of the stiffness, S and contact radius, a over one cycle of oscillation, respectively.
Hence, a stiffer region will correspond to a greater value of E* and Δφ0.
The lower modulus of neat rubber results as brown, which may be due to the deeper inden-
tation of the cantilever in the sample. However, phase images of the filled samples exhibit three
shade differences: brown for the matrix, light green for the matrix near clay particles (interface
region) and white for the clay particles.
Ganguly and Bhowmick used Atomic force microscopy (AFM) for qualitative phase mor-
phological mapping as well as quantitative investigation of surface forces at constituting blocks
and clay regions of a thermoplastic elastomeric nanocomposite based on triblock copolymer:
poly (styrene- ethylene-co-butylene- styrene) (SEBS) and organically modified nano-clay.273
Mapping of elastic modulus of the glassy and rubbery blocks and clay regions was probed by
employing Hertzian and Johnson-Kendall-Roberts (JKR) model from respective approaching
and retracting parts of force-distance curves. The figure below illustrates the procedure of map-
ping forces from f-d curves with sample deformation during interaction (Figure 20).
 ELASTOMER NANOCOMPOSITES 409

FIG. 20. — Procedure of mapping forces from f-d curves with sample deformation during interaction.

In order to determine the elastic properties of SEBS nanocomposites in its different consti-
tuting zones, the corrected force-distance curve was fitted to the Hertz model,

π.k.Δ.(1 − ν 2 )
∂= (2)
2.E tan α

where ∂, depth of penetration on the domains as shown in Figure 20; and E, the modulus from
load curve (the contact portion of force curves); α is the half angle of the tip geometry; k.Δ gives
the force exerted on SEBS sample. Modulus (Esample) can be calculated from ∂, using

∂ = ( z ∗ − d ∗) = 0.825 ⎢ (
⎡k2 R + w
tip sample ( ) 2
. 1 − ν 2 sample ) ⎤
⎥.( d ∗)2 3
⎢ 2
Esample . Rtip .wsample ⎥ (3)
⎢⎣ ⎥⎦

and assuming the AFM tip apex as sphere and the AFM cantilever as a spring attached to the
sphere in series. The penetration by the tip, ∂ is measured from difference between cantilever tra-
versed (z*-d*), where |z*=z-z0|, the distance traversed from just contact point (z*) to present z
scan position (Z0) calculated from force plot and the term |d*=d-d0|, the difference between non
contact deflection (d0) and present deflection (d) at present z position. k is the spring constant
(0.12 Nm-1) for contact mode AFM tip, Rtip is the radius of curvature of the hemi-spherical por-
tion of the apex of the contact mode tip, ~10nm, wsample is assumed to be the lamellar width or
thickness of the domains or the clay regions on the surface of nanocomposite under investiga-
tion. νsample is the poison's ratio of the selected segments on the surface, namely soft PEB (0.5),
harder PS (0.33) and clay (0.25).
Esample was calculated for constituting domains of SEBS-PS and PEB and nanoclays regions
in the SEBS-clay nanocomposite from the Equation 3 and was provided in Table III, where mod-
ulus of the clay platelets was found to be 102 MPa, while the modulus for PS and PEB blocks
410 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

were determined to be 22 and 12 MPa, respectively. These modulus values tallied with the slow
strain-rate macro mechanical tensile data of 26 MPa for SEBS-clay nanocomposite (Table III).
The lower calculated modulus values of nanoclays compared to the literature may be due to
adhering soft rubber on the nanoclays which reduces the overall modulus of clay regions in the
composite.
Due to adhesive interaction in retracting portion of the f-d curve, JKR model registered bet-
ter insight into nano-mechanical measurements of forces, where large deformation and adhesive
energy was involved. Elastic modulus of the sample could be obtained from JKR theory by

JKR
Fadh (1 − ν 2 )
ESample ≈ 0.95 ∗ (4)
R ∗ ∂3

where Fadh is the pull-off force; ν is the poison's ratio; R is the radius of curvature of the probe
tip; and ∂ is the localized sample deformation in PS or PEB or clay regions in SEBS-clay
nanocomposite (Figure 20).
From the calculation in Equation 4, the softer PEB region was shown to have maximum
adhesive force in nature with the calculated modulus in the range of 15±1MPa (Table III). The
harder PS domains found to have modulus in the range of 24±1 MPa in the SEBS-clay nanocom-
posite. The non attractive clay regions generally did not fit the JKR model. This was the reason
for obtaining much less modulus than that of the literature values for clays in the GPa range. The
discussion infers that the bulk modulus of the SEBS clay nanocomposite (26±1 MPa as shown
in Table III) was dictated by the contribution from PS domains in the matrix.

TABLE III
MODULUS OF SEBS-CLAY NANOCOMPOSITES FROM MODELS AND ITS ACTUAL BULK MODULUS
Block and clay Modulus from Localized Modulus from Bulk modulus a)
regions of SEBS Hertz Model, sample JKR Model, of SEBS-clay
nanocomposite (E Sample), MPa deformation, (EJKR Sample) nanocomposite,
(∂), nm MPa MPa
Soft PEB 12 ± 1 50 15±1 26±1
Hard PS 22 ± 1 30 24±1
Clay 100 ± 5 02 105±5
a) Measured with 50mm/min strain rate in Universal Testing Machine Zwick 1445, Ulm, Germany.

Figure 21 a-b shows the dispersion of LDH particles by means of topographic and phase
contrast images of EPDM/LDH nanocomposite.131 The brighter phase in Figure 21a corresponds
to the LDH particle and the darker areas represent the EPDM matrix. The large sheet (50-100 nm
in the horizontal direction) in the higher magnification topographic image area in Figure 21b
shows an average thickness of ~18 nm which is somewhat higher than their individual LDH
platelets and, possibly, is due to stacking.
 ELASTOMER NANOCOMPOSITES 411

FIG. 21a-b. —- Tapping mode AFM phase contrast images depicting

the dispersion of LDH particles in EPDM/LDH nanocomposite.131

B. SPECTROSCOPY

SSNMR. — In recent years, solid-state nuclear magnetic resonance (SSNMR) spectroscopy

specifically high-power proton decoupled 13C CP/MAS NMR has been established as one of the
powerful tools for the investigation of structure, conformation, and dynamics of polymers and
composites. The advantages of solid-state NMR are its ability to probe both the surface and the
bulk of the polymer nondestructively.
This technique has been explored to study polymer-clay nanocomposites- the dynamics of
adsorbed molecules on the mineral surface and their orientation inside the galleries. Clay exfoli-
ation is measured by relaxation times of hydrogen that monitors the iron in montmorillonite.275-278

EPR. — Use of EPR is done to directly measure and understand interface between polymer
and clay organic treatment. However, overall clay dispersion is not measured by this technique,
only the structure and mobility of the surfactant in relation to the polymer is studied.279,280

RAMAN. — Raman spectroscopy has been widely used to characterize the degree of 'in-
plane' perfection of graphitic carbons. The disorder in a carbon system has been correlated with
the ratio of the intensities of the g peak (at ~1575 cm-1) and d peak (at ~1355 cm-1), the line
widths and the frequency of the g peak.290,291
Shown below (Figure 22a) is the characteristic Raman Spectra and Raman Breathing Modes
(Figure 22b) of untreated multiwalled carbon nanotube(CNT), along with those of acid (XNT),
amine (ANT) and silane (SNT) treated multiwalled carbon nanotubes.137
412 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 22a. — Raman spectra of untreated (CNT), acid (XNT), amine (ANT)
and silane (SNT) treated multiwalled carbon nanotubes.

FIG. 22b. — Raman radial breathing modes of untreated (CNT), acid (XNT),
amine (ANT) and silane (SNT) treated multiwalled carbon nanotubes.137

VII. STRUCTURE AND PROPERTIES OF DIFFERENT

ELASTOMERIC NANOCOMPOSITES
Nanocomposites consisting of an elastomer and a small amount (~5 wt%) of different
nanofillers frequently exhibit remarkably improved mechanical and material properties when
compared to those of pristine elastomers. Improvements include a higher modulus, increased
strength and heat resistance, decreased gas permeability and flammability. The structure and
properties of different nanocomposites based on various elastomers and nanofillers are discussed
below.
 ELASTOMER NANOCOMPOSITES 413

A. NATURAL RUBBER (NR), POLYISOPRENE (IR) AND EPOXIDIZED NATURAL RUBBER (ENR)

NR is the most widely used naturally occurring rubber. The literature search shows that sev-
eral research groups have prepared nanocomposites based on this rubber.164,220,229,234,238,292-295
Varghese et al. prepared NR based nanocomposite by melt intercalation method, which is very
useful for practical application. They studied the properties of NR-epoxidized natural rubber
(ENR) blend nanocomposite also.234 Netrabukkana and Pattamaprom studied the effect of com-
patibilizing agents on mechanical properties of natural rubber-montmorillonite clay nanocom-
posites.292 The results indicated that surface treatment of the clays with Si-69 rendered superior
tensile strength to the rubber compound. Jia et al. studied the combined effect of nano-clay and
nano-carbon black on properties of NR nanocomposites and observed that there is a synergistic
effect of the fillers.294 Wu et al. prepared rubber-pristine clay nanocomposites by co-coagulating
rubber latex and clay aqueous suspension.295 Same type of work was also done by Wang et al.216
Effect of radiation cross-linking on nanocomposites properties was studied by Sharif et al.296
Effects of epoxidized natural rubber as a compatibilizer in melt compounded natural rubber-
organoclay nanocomposites, were investigated by Teh et al.237,239,297 Vulcanization kinetics of
natural rubber-organoclay nanocomposites were studied by Lopez-Manchado et al.236 The effect
of different nanoclays on the mechanical properties of NR based nanocomposites was studied.
The tensile properties of different nanocomposites are shown in Figure 23.136

FIG. 23. — Effect of various clays on NR based nanocomposites (at 4 phr loading).

Mechanical properties and cure characteristics of NR nanocomposites were studied by sev-

eral researchers.298,299 Kim et al. studied the effect of nanoclays on the properties of NR/butadi-
ene rubber blend.300
Nanocomposites of natural rubber latex and layered silicates were prepared by a mild dis-
persion shear blending process by Valadares et al.301 The XRD and microscopy results showed
that clay particles were well dispersed in the dry latex and the platelets have a preferential ori-
entation, forming translucent nanocomposites. These showed mechanical properties analogous to
those obtained with vulcanized rubber as well as increased solvent resistance, which was expect-
ed considering that there was significant adhesion between clay lamellae and rubber. There are
more literatures on latex compounding for preparation of NR nanocomposites.216,302-304
The viscoelastic and dielectric properties of nano structured layered silicates reinforced nat-
ural rubber (NR), carboxylated styrene butadiene rubber (XSBR) and their blends have been ana-
414 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

lyzed by Stephen et al.305 They reported increments in the dielectric permittivity of the samples
with the incorporation of nano-fillers. The volume resistivity decreased due to the enhanced con-
ductivity of filled samples.
A novel natural rubber/silica (NR/SiO2) nanocomposite with a SiO2 loading of 4 wt% was
developed by latex compounding with self-assembly techniques.306 The SiO2 nanoparticles were
homogeneously distributed throughout the NR matrix as spherical nano-clusters with an average
size of 75 nm. In comparison with the host NR, the thermal resistance of the nanocomposite was
significantly improved.306 A small amount of synthetic precipitated amorphous white silica
nanofiller, pre-treated with bis(3-triethoxysilylpropyl-)tetrasulphide (TESPT), was used to
crosslink and reinforce natural rubber (NR) by Ansarifar et al.307 The silica particles were fully
dispersed in the rubber, which was cured primarily by using sulfur in TESPT. The properties
were also enhanced when the filled rubber was cured primarily by using sulfur in TESPT.
Natural rubber vulcanizates were reinforced with in-situ formed silica particles using a sol-
gel process.308 The sol-gel nanocomposites showed much higher London dispersive component
of free energy compared with conventional melt-mixed composites. The abrasion resistance of
the nanocomposites was proven to be superior to that of conventional composites.309
Effect of carbon nanoparticles, nanotubes and graphite nanoparticles on the mechanical and
physical properties of NR nanocomposites has also been studied.202,223,299,310 Carbon black poly-
meric nanocomposites were studied on macro- and nanoscales, using polyisoprene as the com-
posite matrix by Knite et al.311 The filler component was an extra conductive carbon black
(Printex XE2, Degussa) with a primary particle diameter of about 30 nm. A very strong reversible
tensoresistive effect of electrical resistance dependence on uniaxial tension deformation was
observed in composites consisting of 10 parts carbon black added to 100 parts of polyisoprene.
A conductive-type atomic force microscope (AFM) was used for the mapping of the carbon
black conductive network into an insulating matrix, while for studying the nanomechanical prop-
erties of composites, a tapping mode atomic force microscope was used.303
Natural rubber, carbon nanotubes and cotton yarns were mixed to give a uniformly mixed
composite containing 15 volume% carbon nanotubes and 3 volume% cotton and exhibiting heat
resistance temperature ≤300 °C.250
The cure parameters of natural rubber compounded with nano ZnO are tabulated in Table
IV.312 The maximum torque value showed an improvement by approximately 12 % for both 5 phr
and 3 phr loading of ZnO nanoparticles in comparison to the conventional rubber grade ZnO,
indicating a better state of cure due to better interaction of ZnO nanoparticles with the matrix
because of reduction in size which leads to an increase in surface area. The difference in maxi-
mum and minimum torque value also improved by 12% indicating an improvement in modulus
and hence the crosslink density. Due to the decrease in dimension of ZnO the area of contact
increases, which results in the improvement of the maximum torque value. The optimum cure
time and scorch time remained almost unaffected. The reversion time was observed to improve
by ~25% for NR-N5 in comparison to NR-RG. Since ZnO makes the elastomer heat resistant,
when ZnO nanoparticles were used instead of conventional rubber grade ZnO, the heat resistance
of the rubber compound increased, preventing the rubber (NR) from degradation, indicating the
improvement in thermal stability of the rubber compound.
 ELASTOMER NANOCOMPOSITES 415

TABLE IV
FORMULATION AND PROPERTIES OF NR COMPOUNDED WITH ZNO NANOPARTICLES
Compound NR-RG NR-N5 NR - N3
Designation
Formulation NR-100 NR-100 NR-100
ZnO - 5 ZnO - 5 ZnO -3
Stearic Acid - 2 Stearic Acid - 2 Stearic Acid - 2
Antioxidant(TQ) - 2 Antioxidant(TQ) - 2 Antioxidant(TQ) - 2
CBS - 0.8 CBS - 0.8 CBS - 0.8
TMTD - 0.2 TMTD - 0.2 TMTD - 0.2
Sulphur - 2.5 Sulphur - 2.5 Sulphur - 2.5
ZnO used Rubber grade ZnO nanoparticles ZnO nanoparticles
Maximum 66.4 74.3 74.5
Torque,(Mh),lb.in

Mh - M l lb. in 65.3 73.5 73.0

Scorch time (min) 5.0 4.6 4.5
Cure time(min) 6.8 6.7 6.6
Reversion time(min) 15.7 19.4 13.8
Cure rate index 54.6 46.2 50.0
( % min-1)
CBS: N-cyclohexyl-2-benzothiazyl sulfenamide; TMTD: Tetramethylthiuram disulfide; TQ: Polymerized 2,2,4-trimethyl
-1,2-dihydroquinoline.

Calcium carbonate-NR latex nanocomposites were prepared by adding nano-CaCO3 whose

surface had been treated with natural rubber latex before sulfuration.116 The physical, thermo-
oxidative aging, and thermal degradation properties and the ultra-microstructure were analyzed.
The structures and properties of nanocomposites could be clearly improved by natural rubber
latex mixed with surface-treated nano CaCO3.
NR nanocomposites with nanometric ZnFeO4,313 cellulose II,228 waxy maize starch,314
chitin whisker,315 nickel and iron nano-particles316 have been studied, as well.
Synthesis and structure-property relationship studies of ENR-in-situ silica nanocomposites
were done by Bandyopadhyay et al.317-321 Figure 24a shows the plots of storage modulus against
temperature, and Figure 24b the loss tangent against temperature for the ENR-silica hybrid
nanocomposites. The modulus gradually increased both in the glassy as well as in the rubbery
regions on increasing the TEOS concentration, due to greater rubber-silica interaction. This is
probably due to more hydrogen bonded interaction between the vicinal diol groups of ENR back-
bone and the silanol groups of in situ generated silica particles (Figure 25).
416 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 24. — Plots of [a] storage modulus versus temperature; and [b] tan delta versus temperature for ENR-silica
hybrid nanocomposites (ENR10=ENR+10 WT.% TEOS, number = TEOS wt.%).

FIG. 25. — Hydrogen bonded ENR-silica interactions.

Figure 26 displays the representative differential thermogravimetry (DTG) plots for ENR-
silica hybrid nanocomposites with increasing TEOS concentrations. The strong rubber-silica
interaction present in ENR-silica system got reflected in the corresponding DTG plots. In the
case of ENR-silica system, Tmax shifted by ~23 °C. Owing to stronger ENR-silica attachments,
the heat energy is being transferred to the filler and thereby the maximum degradation tempera-
ture shifts to higher temperature.
 ELASTOMER NANOCOMPOSITES 417

FIG. 26. — ENR-silica hybrid nanocomposites (letter 'D' in legends indicates

dicumyl peroxide (DCP) crosslinked samples, and number = TEOS wt.%)

The distribution of modified and unmodified nanoclays in the rubber phases in blends com-
posed of natural rubber and epoxidized natural rubber, and natural rubber and polybutadiene rub-
bers too have been discussed.322 Different clays, modified and unmodified ones, were melt mixed
into these blends and their distribution studied with the help of dynamic mechanical properties.
AFM and XRD were used to further substantiate the observations. Specific interaction and vis-
cosity were found to control the distribution pattern.

B. POLYBUTADIENE RUBBER (BR)

Detail morphology, mechanical and optical properties of BR nanocomposites along with

filler loading were investigated by Wang et al.323-325 Sadhu and Bhowmick studied the mechan-
ical and rheological properties of BR-organoclay nanocomposites.169,326 They showed that the
die-swell was much lower (Figure 27) in the case of MMT filled sample (BRN4) than the organ-
oclay filled one (BROC4), as the organoclay was not exfoliated in BR (Figure 28).

FIG. 27. — Die-Swell versus log shear rate of BR and its nanocomposites.
418 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 28. — XRD spectra of nanocomposites based on BR.

The effects of the incorporation of inorganically and organically modified clays on the vul-
canization reactions of BR were analyzed using rheometry and differential scanning calorimetry
by Song et al.327 They observed that the organoclays favored the vulcanization process although
the vulcanizing effect was reduced with increasing clay content. Kim et al. studied the effect of
varying modifier concentration of organoclay on the vulcanization behavior and mechanical
properties of BR/organoclay hybrid.328 The order of the torque difference was BR/Cloisite 15A
> BR/Cloisite 10A > BR/Cloisite 20A > BR/Cloisite 25A > BR/Cloisite 30B > BR/Cloisite Na+,
and the order of vulcanization rate also showed similar trend. The organoclay with largest quan-
tity of modifier gave larger torque difference and faster vulcanization rate to the BR/organoclay
nanocomposites. The possible formation of a Zn complex in which sulfur and long chain ammo-
nium modifiers participate, might facilitate the formation of crosslinks.
The rheological properties of liquid polybutadiene rubber/organo-clay nanocomposite gels
were investigated by Wang et al.,329 focusing on the effects of clay exfoliation and orientation-
disorientation as well as polymer-clay interaction and temperature. Both irreversible and
reversible viscosity transitions were observed in the temperature range from 26 to 136 °C in
steady shear experiments on as-prepared and exfoliated samples. These transitions were depend-
ent strongly on the end groups, molecular weight of the liquid rubber and the shear field. The
irreversible transition was attributed to the exfoliation of the clay, and the reversible transition
can be understood as a shear-induced orientation-disorientation transition of the clay sheets.
Polymer-clay interaction was confirmed to be a key-controlling factor of the orientation-disori-
entation transition, whereas the shear field played a critical role to induce such a transition.
Liao et al. investigated BR/organically modified montmorillonite nanocomposites along
with polyisoprene and styrene-butadiene rubber-nanocomposites prepared by in situ anionic
intercalation polymerization.330 The results showed that a certain extent of exfoliated nanocom-
posites could be prepared by in situ anionic polymerization. The incorporation of organoclay
obviously changed the microstructure of BR; the concentrations of the 1,2-unit, 3,4-unit, and
trans-1,4-unit increased dramatically with an increasing concentration of organoclay and the con-
centration of the cis-1,4 structure decreased. Organoclay apparently strengthened the rubber
matrix; eg., the tensile strength and hardness of nanocomposites increased greatly, but the per-
 ELASTOMER NANOCOMPOSITES 419

manent deformation did not change much.

An effect of nanosize CaCO3 on physical, mechanical, thermal and flame retarding proper-
ties of BR was compared with conventional CaCO3 and fly ash filled BR by Mishra and
Shimpi331 and the increment in properties was most pronounced in the smallest [9 nm] size
CaCO3.

C. STYRENE-BUTADIENE RUBBER (SBR)

This is the most commonly used synthetic rubber. There are several studies carried out on
this rubber. Different researchers observed very interesting effect of nanoclays on various prop-
erties of this rubber.43,169,212,229,295,326,327,332-341 Sadhu and Bhowmick studied the effect of dif-
ferent clay modifiers on the properties of nanocomposites.43 Figure 29 shows the variation in
mechanical properties of SBR-clay nanocomposites due to change in the chain length of the
amine modifiers. It is clear that there is an increase in tensile strength when the system contain-
ing the modified clay is compared with the one having the unmodified clay.

Fig. 29. — Variation of mechanical properties with variation in carbon atoms

in the amine chains for MMT-SBR composites.

The X-Ray diffractograms of the SBR based nanocomposites with unmodified and modified
clay are given in Figure 30 a-b.169,326 Improvement in tensile strength varied depending on the
nature of rubber. With higher styrene content the tensile strength increased in nanocomposites. A
plot of variation in magnitude of properties with percent styrene content is given in Figure 31.
420 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 30. — X-Ray Diffractograms of unmodified and modified nanoclays and SBR
based nanocomposites with styrene content of (a) 15% and 40% (b) 23%.

FIG. 31. — Variation in mechanical properties with styrene content in SBR based nanocomposites.

Detailed morphology studies of SBR-clay nanocomposites were also conducted by Sadhu

and Bhowmick.333 The AFM photomicrographs of SBR-organoclay nanocomposites at two dif-
ferent magnifications clearly show that the clay particles are exfoliated and uniformly dispersed
within the matrix (Figure 32 a-b). The average particle thickness lies in the range of 15-20nm
with an aspect ratio of around 100.
 ELASTOMER NANOCOMPOSITES 421

a) b)
FIG. 32 — AFM photographs of SBR-organoclay at [a] low and [b] high magnifications.

A study on flammability of montmorillonite-SBR nanocomposites was done by Zhang et

al.334 Effect of pressure as a critical factor governing final microstructures of cured nanocom-
posites was analyzed by Liang et al.335 Influence of fillers on free volume and gas barrier prop-
erties in SBR nanocomposites was also studied using positrons.336 Wu et al. used a modulus
reduction factor of 0.66 for platelet type of fillers and showed that the modified Halpin-Tsai
model fitted well into the experimental data obtained in SBR nanocomposites.337 Several
researchers prepared the nanocomposites from latex and studied the morphology and mechani-
cal properties.338-340
SBR/MMT nanocomposites were successfully synthesized by in situ living anionic poly-
merization with n-BuLi as initiator.342 The results from kinetics study and 1H NMR indicated that
the addition of organophilic montmorillonite (OMMT) did not change the living copolymeriza-
tion and the components of the copolymer on the whole when OMMT content was lower than 3
wt%. However, gel permeation chromatography showed that the introduction of OMMT result-
ed in small amount of high-molecular weight fraction of SBR in the composites, leading to an
increase in the weight average molecular weight and polydispersity index, but the number aver-
age molecular weight remained unaltered. The results from transmission electron microscopy
and X-ray diffraction revealed that a completely exfoliated structure existed in the nanocompos-
ite with 25 wt% styrene and OMMT content from 1 to 4 wt%, and styrene played an important
role in the expansion of OMMT layers. Moreover, the nanocomposites possessed higher glass-
transition temperature, thermal stability, tensile strength and elongation at break than SBR when
the OMMT content ranged from 2.5 to 4 wt%.
Carbon nanotubes (CNTs) filled powder styrene-butadiene rubber (SBR) composites were
prepared by spray drying of the suspension of CNTs in SBR latex.343 The powder was spherical
like and uniform with an average diameter of less than 10 nm. The dispersion of CNTs in the
rubber matrix was improved remarkably compared with that in the rubber composites obtained
by the conventional mechanical mixing method. Further study about the effect of CNTs on the
prepared SBR composites was performed by analyzing the vulcanization process of the SBR
powder, thermal and mechanical properties of the vulcanized SBR composites. Differential scan-
ning calorimeter (DSC) analysis indicated that the glass transition temperature of SBR compos-
ites increased with the increasing ratio of CNTs. The vulcanization process showed that CNTs
could decelerate the vulcanization of the SBR composites. Dynamic mechanical analysis indi-
422 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

cated that the storage modulus of the composites was improved with the CNTs additions, espe-
cially when the CNTs addition exceeded 30 phr. Compared with pure SBR composites, the hard-
ness, tensile and tear strengths of the composites filled with 60 phr CNTs enhanced by 73.9%,
327.7% and 191.1%, respectively, which should be ascribed to the excellent mechanical proper-
ties of CNTs and uniform dispersion of CNTs in the rubber matrix.
Styrene-butadiene rubber as a matrix was reinforced separately with nano-CaCO3, fly-
ash252,253 and CaSO4 by Mishra and Shimpi.256 A reduction in the nanosizes reportedly enhanced
the mechanical, physical and thermal properties of the rubber nanocomposites.
Conductive nanocomposites were prepared using styrene-butadiene rubber as the polymer
matrix and nanosized powder of copper-nickel (Cu-Ni) alloy as the filler.344 The filler loading
was varied from 0 to 40 phr. The electrical conductivity of filled polymer composites is due to
the formation of some continuous conductive networks in the polymer matrix. The DC volume
resistivity was measured against the loading of the nanofiller to check the percolation limit. The
effect of temperature, applied pressure, and time duration under constant compressive stress on
the DC resistivity and AC conductivity of the composites with different filler loading were inves-
tigated. The change in DC resistivity and AC conductivity against temperature of these compos-
ites exhibited positive coefficient of temperature. With the change in applied pressure and time
duration under constant compressive stress, the DC resistivity undergoes an exponential
decrease.

D. ACRYLONITRILE-BUTADIENE RUBBER (NBR)

Different NBR and carboxylated acrylonitrile butadiene rubber (XNBR)-clay nanocompos-

ites were prepared by various workers all over the world using melt, solution and latex blending
techniques and their properties were also investigated.169,219,242,243,295,326,332,333,337,344-351
Vulcanization kinetics was studied by Choi et al. using rheometer and DSC. The activation ener-
gy of curing of NBR- nanocomposites was lower than that of pristine NBR.345 Effect of differ-
ent acrylonitrile content on the mechanical, dynamic mechanical and rheological properties of
nanocomposites was explained by Sadhu and Bhowmick.169,326,332 The polymers with highest
acrylonitrile content gave larger enhancement of properties (Table V).

TABLE V
MECHANICAL PROPERTIES WITH VARYING DEGREES OF POLARITY OF RUBBER
Sample Tensile Elongation Modulus at Volume Fraction
Designation Strength at Break 50% of Rubber
(MPa) (%) Elongation in Swollen Gel
(MPa) (Vr)
19NBR 3.00 362 0.66 0.332
19NBRN4 a) 2.73 147 1.00 0.359
19NBROC4 a) 3.60 154 1.23 0.436
34NBR 2.10 399 0.53 0.215
34NBRN4 2.00 279 0.68 0.219
34NBROC4 4.85 923 0.52 0.150
50NBR 2.75 553 0.55 0.178
50NBRN4 2.10 414 0.57 0.224
50NBROC4 5.60 679 0.65 0.264
a) 19NBROC4 = nitrile rubber with 19% acrylonitrile + 4phr octadecyl amine modified MMT, 19NBRN4 = nitrile rub-

ber with 19% acrylonitrile + 4phr MMT.

 ELASTOMER NANOCOMPOSITES 423

The nanoclay influenced the dynamic mechanical properties of the rubbers to a great extent
even at a smaller loading of 4 phr (Figure 33). The storage modulus, the loss modulus and the
tan delta were found to be functions of degrees of intercalation and interaction.

FIG. 33. — log E' vs log strain plot of 50NBR and its nanocomposites.

These properties were also affected by the nature and polarity of the base rubber as the
degrees of intercalation and interactions are changed. For instance, the storage modulus
increased with loading of organoclay in all the NBRs. But the extent of increase was maximum
in the case of 50NBR system.
Shear viscosity is plotted against shear rate in Figure 34 for 34NBR and its nanocomposites
at 130 °C. The viscosity continuously decreased with increasing shear rate i.e. shear thinning
effect occurred for all the systems, obeying the power law equation. Surprisingly, the shear vis-
cosity of the 34NBROC4 was lower than that of the 34NBRN4, which was still lower compared
to that of the 34NBR. A similar behavior was observed at 110 °C and 120 °C also.

a) b)

FIG. 34. — (a) The log Shear Viscosity vs log Shear Rate of 34NBR and its nanocomposites at 130 °C ; and (b) SEM
photographs depicting die-swell behavior of extrudates of (i) 34NBR; (ii) 34NBRN4; and (iii) 34NBROC4.
424 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

These investigations illustrated that the processability improved on incorporation of the

unmodified and the modified nanofillers. This was an unique behavior of these nanocomposites.
The polarity of the rubber also affected the processing behavior of these nanocomposites. The
higher the polarity, the higher was the decrease in shear viscosity with the incorporation of the
nanoclay.
The role of the type of organic modifier used with montmorillonite on the formation of
nanocomposites in melt compounding process was studied by Kim and White.346 They showed
that the quaternary ammonium ion modified organoclays had superior compatibility compared to
the primary, secondary, and tertiary ammonium ion modified organoclay. Kim et al. studied the
curing and barrier properties of NBR-organoclay nanocomposites.347
Effect of two different antioxidants, p-phenylene diamine (IPPD) and 2,2,4-tri-methyl-1,2-
dihydroquinoline (TMQ), on the degradation process when they were incorporated into
nanocomposites based on an NBR matrix reinforced with SiO2 was investigated.352 The effect of
silica nanofiller on vulcanization parameters and thermal and mechanical properties of vulcan-
ized carboxylated nitrile rubber was investigated, as well.353 Zinc ion-coated nanosized silica,
uncoated nanosized silica, and conventional silica fillers were used at 5 phr loading. The zinc
ion-coated silica provided better reinforcing and curing characteristics, and the fact was
explained in terms of interaction at the molecular level forming an ionomer rubber. The sul-
fur/mercaptobenzothiazole vulcanization system was found to provide vulcanizates with superi-
or thermal stability, mechanical properties, and interfacial adhesion compared to the methylene-
dianiline/diphenylguanidine curative system.
Nanocomposites of nitrile rubber (NBR) and cellulose II were prepared by co-coagulation
of nitrile rubber latex and cellulose xanthate mixtures.354 The effect of the addition of increasing
amounts of cellulose II, varying from 0 to 30 phr, on the mechanical behavior of a NBR was ana-
lyzed.
The effect of different solvent combinations on solution mixing of hydrogenated nitrile rub-
ber (HNBR)-sepiolite nanocomposite has been studied by Chowdhury and Bhowmick. Use of
appropriate solvent combination resulted in remarkable improvements in thermal, mechanical
and optical properties of the nanocomposite in comparison to the neat rubber.355
The effect of curative package showed an interesting effect on the morphology of the hydro-
genated nitrile rubber nanocomposites.356-358 The sulfur vulcanization, in combination with pri-
mary amine intercalants of clay produced a confined clay structure, while the peroxide curing
yielded well-ordered intercalated nanocomposites.356
Two methods for preparation of hydrogenated nitrile rubber (HNBR)/carbon nanotube
(CNT) nanocomposites were described by Yue et al.359 In order to study the effect of CNTs on
the vulcanization of composites, two kinds of vulcanizing agents, dicumyl peroxide and 2,5-
dimethyl-2,5-ditert-butyl peroxy hexane, were applied for curing of the composites based on
HNBR. The crosslinking processes and the mechanical properties of the composites were deter-
mined.
Sahoo and Bhowmick100 have reported ZnO nanoparticle synthesis and its application as
curatives in carboxylated nitrile rubber (XNBR). ZnO nanoparticles possess greater surface to
volume ratio. When used in XNBR as curative, ZnO nanoparticles showed excellent mechanical
and dynamic mechanical properties. The ultimate tensile strength increased from 6.8 MPa in
ordinary rubber grade ZnO-XNBR system to 14.9 MPa in nanosized ZnO-XNBR, without sac-
rificing the elongation at failure values.

E. ETHYLENE PROPYLENE DIENE METHYLENE LINKAGE RUBBER (EPDM)

EPDM-clay nanocomposites were prepared using both solution and melt blending tech-
niques by various workers.229,233,245,360-375 Ma et al. studied the influence of ethylene content on
 ELASTOMER NANOCOMPOSITES 425

the properties of nanocomposites.233 Acharya et al. established structure-property relationship

for EPDM-clay nanocomposites.245,360,376 Study of mechanical and thermal properties shows sig-
nificant improvement over the gum. The results of latter properties are given in Table VI.
The results suggest that the thermal stability improves with higher loading till 6 phr of nan-
oclay and this improvement is attributed to the barrier effect of the exfoliated and the intercalat-
ed nanoclay particles.

TABLE VI
THE THERMAL DEGRADATION RESULTS OF EPDM AND ITS NANOCOMPOSITES
Sample Initial Thermal Final Decomposition Weight
Decomposition, Temperature, Loss (%)
Ti (°C) Tf (°C)
Pure EPDM 325 460 96.4
EPDM+2wt% 16Me-MMT a) 341 459 95.2
EPDM+3wt% 16Me-MMT 355 460 92.2
EPDM+4wt% 16Me-MMT 372 461 92.1
EPDM+5wt% 16Me-MMT 372 460 92.0
EPDM+6wt% 16Me-MMT 374 462 91.8
a) 16Me-MMT = hexadecyl amine modified MMT.

The UV-light induced oxidation of EPDM-clay nanocomposites compatibilized with

EPDM- grafted - maleic anhydride was studied.362 Compatibilizer effect of grafted glycidyl
methacrylate (GMA) on EPDM-organoclay nanocomposites was investigated by Gatos et al.365
The combined action of the curatives and GMA resulted in better intercalation and enhanced
mechanical behavior of the rubber nanocomposites. A comparison between cure systems for
EPDM-montmorillonite nanocomposites was studied.368 It was shown that the clay was exfoli-
ated and dispersed uniformly in the EPDM composites cured with sulfur, while it was stacked
with several layers and existed in an intercalated structure in the composites cured with perox-
ide. Chang et al. modified sodium montmorillonite by treating it with octadecyl ammonium ion
and then mixed it with EPDM oligomer.371 They observed tremendous improvement in tensile
strength, tear strength, dynamic storage modulus and oxygen gas permeability.
Effect of organoclay on the cure characteristics of EPDM-conventional sulphur vulcaniza-
tion system was investigated by Mousa.372 Improvement in cure characteristics was attributed to
the small size of the filler particles and to the amine functionality in the organoclay structure.
Kang et al. studied several compatibilization approaches, including the addition of EPDM
modified with maleic anhydride (EPDM-g-MA) and the use of organoclay modified with male-
ic anhydride-grafted liquid vinyl polybutadiene (LVPB-g-MA).377 The use of LVPB-g-MA-mod-
ified organoclay increased the degree of dispersion as measured by X-ray diffraction, giving
increased thermal stability, modulus and decreased swelling. Flame resistance was poorer for the
EPDM/LVPB-g-MA- modified organoclay system compared to the unmodified EPDM/organ-
oclay compound.
Acharya et al. also established structure-property relationship for EPDM-LDH nanocom-
posites.131,378 Partially exfoliated morphology of EPDM-modified LDH is shown in Figure 35.
426 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 35. — TEM image of EPDM/LDH nanocomposite.

The tensile measurement shown in Figure 36 clearly indicates the reinforcing effect of LDH
as filler in the EPDM matrix.

FIG. 36. — Tensile Strength (TS) and Elongation at break (EB) of EPDM/LDH nanocomposite.

The well-dispersed rigid modified-LDH layers efficiently transferred stress from polymer
and directly enhance the stiffness in the corresponding nanocomposites. Interestingly, the elon-
gation at break (EB) also increased with the modified-LDH content. This increase may be due to
the platelet orientation or chain slippage or plasticization.

F. BUTYL RUBBER (IIR)

Isobutylene isoprene rubber (IIR)-clay nanocomposites were prepared successfully by sev-

eral researchers.170,229,379-381 Kato et al. prepared them by melt intercalation with maleic anhy-
dride-grafted IIR (Ma-g-IIR) and organophilic clay. With the addition of 15 phr clay, gas barrier
properties of the nanocomposites were 2.5 times greater than those of Ma-g-IIR.379 The effects
of heat and pressure on microstructures of IIR-clay nanocomposites prepared by solution inter-
calation (S-IIRCN) were investigated by Lu et al.380 They suggested through various experiments
that the presence of residual solvent molecules in S-IIRCN played a key role on the microstruc-
tural change of S-IIRCN caused by heat and pressure. Liang et al. proposed guidelines for
 ELASTOMER NANOCOMPOSITES 427

designing curing system to achieve desired intercalated/exfoliated morphology.381 In another

work, Liang et al. showed that the aspect ratio of clay layers in S-IIRCN is larger than that in
melt intercalated sample.170
A special kind of butyl rubber is brominated polyisobutylene-co-paramethylstyrene (BIMS).
BIMS based nanocomposites were prepared by Maiti et al.171 The nanocomposite were prepared
in solution intercalation method using various organoclays and their mechanical, dynamic
mechanical and rheological properties were measured and explained with reference to the XRD
and TEM results. The increment in barrier properties in the case of the modified clay filled BIMS
was remarkable when compared with that of the gum vulcanizate (Figure 37).

FIG. 37. — Barrier property of BIMS-nanocomposites.

The rubber showed partially exfoliated morphology with organo-clays (Figure 38).

FIG. 38. — TEM micrograph of BIMS/organoclay nanocomposite.

They also studied the effect of nanoclays in conventional carbon black and silica filled sys-
tems. The nanoclays exhibited a synergistic effect with conventional fillers (Figure 39).382
428 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 39. — Stress-strain curve of BIMS with 4 phr organoclay [BIMSOC4], BIMS with 20 phr FEF black
[BIMSFEF20] and BIMS with 20 phr FEF black and 4 phr octadecylamine modified clay [BIMSFEF20OC4].

Tsou and Measmer examined the dispersion of organosilicates on two different butyl rub-
bers viz. BIMS and brominated poly(isobutylene-co-isoprene) (BIIR) with the help of SAXS,
WAXS, AFM and TEM.383
There are patents and papers on low permeability and improved barrier properties of butyl-
rubber nanocomposites.384-387

G. POLYOLEFIN ELASTOMER (POE)

Ray and Bhowmick studied the effect of montmorillonite clay-polyacrylate hybrid material
on the properties of poly(ethylene-octene) copolymer.42 Preparation and properties of organical-
ly modified nanoclay and its nanocomposites with poly(ethylene-octene) copolymer were report-
ed by Maiti et al.388 Excellent improvement in mechanical properties (Figure 40) and storage
modulus was noticed by them. The results were explained with the help of morphology, disper-
sion of the nanofiller, and its interaction with the rubber.

FIG. 40. — Tensile stress-strain curve of poly(ethylene-octene) copolymer with different clays [EN = neat poly(ethyl-
ene-octene) copolymer, ENUN4 = EN + 4phr MMT, ENOC4 = EN+ 4phr organically modified MMT].
 ELASTOMER NANOCOMPOSITES 429

Liao and Wu prepared new nanocomposites from poly(ethylene-octene) elastomer, mont-

morillonite and biodegradable starch by means of a melt blending method.389 They showed that
the nanocomposites could provide a stable tensile strength when the starch content was up to 40
wt %. Chang et al. produced microcellular foam from this elastomer.390

H. CHLOROPRENE RUBBER (CR)

A few studies have been reported on chlorine containing elastomers like chloroprene rubber,
chlorinated polyethylene rubbers.216,391-393 CR-clay nanocomposites were prepared by co-coag-
ulating the rubber latex and clay aqueous suspension and the properties of the nanocomposites
were compared with conventional carbon-black filled systems.216
Ultrafine silica-dispersed, heat resistant polychloroprene adhesive compositions were devel-
oped by Sunada et al.394
Kar and Bhowmick395 developed MgO nanoparticles and investigated their effect as cure
activator for halogenated rubber. MgO nanoparticles were able to enhance the thermal stability
of CR (Table VII). Similarly, ZnO nanoparticles were effective as both curing agent and cure
activators in polychloroprene rubber.175

TABLE VII
EFFECT OF NANO MGO ON THERMAL PROPERTIES OF CR
Sample Ti(°C) Tmax(°C) Residue (%) Maximum rate of
degradation (%/°C)
CR +ZnO + 352 353 28 6.3
MgO (conventional)
CR + ZnO + 367 381 27 1.7
MgO (nanoparticles)

I. POLY(ETHYLENE-CO-VINYLACETATE) (EVA)

This rubber was used as matrix by several researchers to study the further improvement of
its inherent thermal and flame retardant properties after addition of nanoclays.396-407 Nishioka et
al. examined three-dimensional structure of EVA-clay nanocomposites by transmission electron
microtomography.408 Effect of surfactant/CEC ratio of organo-clay on the thermal properties of
EVA nanocomposites was also studied.398 Effects of clay nature and organic modifiers on mor-
phology, mechanical and thermal properties were investigated by Peeterbroeck et al.403
Morphological influence on mechanical properties, crystallization, shear and extensional rheol-
ogy of EVA-layered silicate-nanocomposites was also studied.409-412 Morphology, mechanical,
thermal and rheological properties of a new ternary EVA- nanocomposite with organo-modified
clays and purified multi-walled carbon nanotubes, prepared via direct melt blending were evalu-
ated.411 The work by Pastore et al. showed the temperature induced structural rearrangements of
nanocomposites based on EVA intercalated-organo modified clay (at 3-30 wt%) which occurred
in the range between 75 and 350 °C.413 Inhibiting effect of aluminosilicate layers on swelling of
EVA-clay nanocomposite was determined by Pramanik et al.414 Studies on structure and proper-
ties of EVA- clay nanocomposites were also carried out by different research groups.415-422
George and Bhowmick synthesized EVA-nanocomposites using expanded graphite (EG).149
Table VIII reports in detail mechanical properties of the cured EVA-EG nanocomposites in terms
of tensile modulus (at 50,100 and 200% elongations), tensile strength and elongation at break
values. With increasing concentrations of the EG, the modulus of EVA increased. A maximum
of ~ 35% increment in the tensile strength, with reference to the virgin EVA was attained.
430 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

Although the tensile strength and modulus increased, the elongation at break did not decrease in
these systems, except for 8 phr filler. Figure 41 a-c depicts the TEM pictures of the EVA-EG
nanocomposites at 4 and 8 phr expanded graphite loading along with that of EVA-4phr natural
graphite (NG). It is clear from Figure 41a that graphite platelets were finely dispersed in the rub-
ber matrix leading to higher interaction between the matrix and the filler particles resulting in
better mechanical properties. The thickness of platelets was observed to be in the range of 20-30
nm, whereas at higher loading (8 phr), the graphite particles exhibited an agglomeration tenden-
cy (Figure 41b), leading to poor overall properties for the composites prepared. The agglomer-
ates existed in the thickness range of 80-120 nm. Similarly, EVA-4NG also exhibited clear
agglomerations with an average thickness more than 100 nm (Figure 41c).

TABLE VIII
MECHANICAL PROPERTIES OF DIFFERENT EVA- EXPANDED GRAPHITE NANOCOMPOSITES
Sample Tensile Strength Elongation Modulus( MPa) at
(MPa) at Break 50% 100% 200%
(%)
EVA 5.54±0.10 310±10 0.72±0.08 1.10±0.10 2.70±0.07
EVA+1EG 6.03±0.14 350±10 0.76±0.10 1.18±0.12 2.82±0.11
EVA+2EG 6.58±0.15 360±10 0.95±0.08 1.54±0.09 3.44±0.07
EVA+4EG 7.51±0.12 320±10 1.26±0.12 2.05±0.10 4.14±0.10
EVA+8EG 4.86±0.10 210±10 1.74±0.10 2.74±0.11 4.67±0.10
EVA+4NG 4.59±0.20 310±10 0.66±0.05 0.94±0.05 1.68±0.10

FIG. 41. — TEM pictures of (a) EVA + 4EG; (b) EVA + 8EG; and (c) EVA + 4NG.

George et al.137 studied the effect of functionalized and un-functionalized MWNT on vari-
ous properties of high vinyl acetate (50 wt %) containing EVA-MWNT composites. Figure 42
displays TEM image of functionalized nanotube reinforced EVA nanocomposite.
 ELASTOMER NANOCOMPOSITES 431

FIG. 42. — TEM image of amine modified nanotube reinforced EVA nanocomposite.

Dynamic mechanical properties of these nanocomposites are shown in Figure 43. There was
10% improvement of the storage modulus at 20 °C by incorporating only 4 wt. % of the nanotube.

FIG. 43. — Variation of storage modulus against temperature for EVA nanocomposites having different loadings of
CNT and amine modified nanotube (ANT) [Number preceding CNT/ANT indicates their loading].

The results obtained by Kuila et al.423 from the ethylene-vinyl acetate elastomer blended
with lamellar-like Mg-Al double hydroxide (LDH) layered nanoparticles demonstrated that mag-
nesium hydroxide nanocrystals possess higher flame retardant efficiency and mechanical rein-
forcing effect in comparison with common micrometer grade magnesium hydroxide particles.

J. ACRYLATES

Nanocomposites have been prepared based on this type of elastomers with a wide range of
nanofillers mostly by in-situ polymerization.424-430 The mechanical, rheological and morpholog-
ical behaviors were investigated thoroughly.
Acrylic copolymer- and 5% acrylic acid (AA) modified terpolymer-hybrids with unmodified
montomorilonite clay (Cloisite Na) and organoclay (Cloisite 10A) were synthesized by in-situ
free radical bulk polymerization.258 XRD results suggested polymer intercalation in both unmod-
ified and organo-modified clay in the copolymer and terpolymer hybrids (Figure 44).
432 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 44. — XRD diagrams of in-situ polymer clay hybrid composites (85E3Na [Ethyl Acrylate (EA) = 85%, Butyl
Acrylate (BA) = 15%, 3phr Cloisite NA], 85E310A [EA = 85%, BA = 15%, 3phr Cloisite 10A], 5A85E 3Na [EA = 85%,
BA = 15%, AA = 5%, 3phr Cloisite NA] and 5A85E310A [EA = 85%, BA = 15%, AA = 5%, 3phr Cloisite 10A]).

AFM analysis further confirmed these results (Figure 45).

FIG. 45. — AFM phase image of hybrid nanocomposite [acrylate terpolymer + 3phr Cloisite 10A].

Cloisite 10A hybrids and the terpolymeric nanocomposites demonstrated superior mechan-
ical and dynamic mechanical properties. Terpolymer-clay hybrids with 9 wt% Cloisite 10A also
showed higher thermal stability. Nanocomposites synthesized in-situ showed better properties
than those prepared in solution method (Table IX).

TABLE IX
COMPARATIVE MECHANICAL PROPERTIES OF COPOLYMER NANOCOMPOSITES PREPARED BY IN SITU AND
SOLUTION PROCEDURES
Sample designation Tensile strength Modulus at 50% Elongation at
(MPa) (MPa) break (%)
85E 0.18 0.13 >800
85E60A in-situ 1.75 0.88 >800
85E60A solution 0.74 0.46 >800
 ELASTOMER NANOCOMPOSITES 433

Acrylic copolymer- and 5% acrylic acid (AA) modified terpolymer-silica hybrid nanocom-
posites were synthesized by free radical bulk polymerization of ethyl acrylate (EA), butyl acry-
late (BA) and acrylic acid (AA) with simultaneous generation of silica from tetraethoxysilane by
sol-gel reaction by Patel et al.431,432 The hybrid samples were characterized by SEM, FTIR spec-
troscopy, NMR spectroscopy, dynamic mechanical, mechanical and thermal properties. SEM
images (Figure 46 a-c) confirmed the presence of nanosilica particles within the polymer matri-
ces, whose dispersion and particle size distribution and visual appearance were dependent on the
relative polarity (hydrophilicity) of the polymer matrices and the concentration of the filler.

FIG. 46. — SEM micrographs of hybrid composites (a) 85EN30 [EA = 85%, BA = 15%,
TEOS = 30%] (b), 5A85EN30 [EA = 85%, BA = 15%, AA = 5%, TEOS = 30%]
and (c) 5A85EN50 [EA = 85%, BA = 15%, AA = 5%, TEOS = 50%].

Patel et al. also studied the nanocomposite adhesives based on these acrylic polymers and
silica or clay prepared by sol-gel or solution blending techniques, respectively.433 Peel force vs.
extension plots for Aluminum (Al) -Aluminum (Al) joints with representative polymer-silica
hybrids are shown in Figure 47. The locus of failure changed from apparently interfacial failure
for neat acrylic copolymer to slip-stick behavior in the case of the hybrid nanocomposite adhe-
sives with higher polarity.
434 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 47. — Peel behavior of Al-Al joints bonded with polymer-silica hybrid adhesives.
(5A85EN30 [EA = 85%, BA = 15%, AA = 5%, TEOS = 30%] and 5A85E [EA = 85%, BA = 15%, AA = 5%]).

The superior reinforcement of the terpolymer hybrids compared to the copolymer hybrids
without affecting their surface characteristics probably played a key role in the improvement of
joint strength. 50 wt% TEOS loaded terpolymer-silica based hybrids (5A85EN50) with Al-Al,
Wood-Wood and polypropylene (PP)- polypropylene (PP) joints exhibited 219%, 174% and
433% improvement over the neat ter-polymer, while in the case of copolymer-silica nanocom-
posites (85EN50), these values were 126%, 216% and 210% at similar TEOS concentration,
respectively. A similar trend was observed in the case of clay-hybrids.
Atom transfer radical polymerization (ATRP) of ethyl acrylate (EA) was carried out in bulk
at 90 °C in presence of organically modified nanoclay as an additive by Datta et al.259 A remark-
able enhancement in the rate of polymerization was observed and it was compared with the
ATRP of EA without nanoclay. Time of dispersion of clay in monomer (Td) prior to polymer-
ization and the extent of clay loading were found to have a positive effect on polymerization rate
(Table X).

TABLE X
VARIATION OF APPARENT RATE CONSTANT OF POLYMERIZATION [kAPP] AS A FUNCTION OF
DISPERSION TIME (OF CLAYa) IN MONOMER) IN ATRP OF EA IN BULK AT 90 °C
Dispersion Sample Sample kapp(s-1), % increase
time (Td) designation designation × 10-5
(of clay in (of resultant
monomer) polymer)
Without clay — — 2.14 —
1h EAD 1 PEAD 1 3.47 62
10 h EAD 10 PEAD 10 7.43 247
20 h EAD 20 PEAD 20 20.68 866
a) Nanoclay used: Cloisite 30B, 2 wt%; Letter ‘D’ stands for dispersion; number (1,10,20) - clay dispersion time in hours.
 ELASTOMER NANOCOMPOSITES 435

The polymerization proceeded through first order kinetics and molecular weights increased
linearly with conversion, close to the targeted molecular weights (Figure 48). The resulting
nanocomposite had exfoliated clay particles, as evident from Wide Angle X-ray diffraction
(WAXD) and Transmission Electron Microscopy (TEM) studies.

FIG. 48. — Plots of Mn and PDI versus monomer conversion for in situ ATRP of EA-clay
nanocomposite at 90 °C with varying dispersion time. [EA]o = 4.9 × 10-2 M. Open symbols represent
polydispersities and filled symbols represent Mn. *Nanoclay used: Cloisite 30B (2 wt%).

The effect of polymer-filler interaction on solvent swelling and dynamic mechanical prop-
erties of the sol-gel derived acrylic rubber (ACM)/silica, hybrid nanocomposites was described
for the first time by Bandyopadhyay et al.317 The structure -property relationship, thermal prop-
erties, rheological properties and the effects of a few reaction parameters, namely, type of sol-
vents, tetraethoxysilane (TEOS)-to-water mole ratio, temperature of gelation at constant con-
centration of TEOS (45 wt.-%) and pH were investigated for acrylic rubber/silica hybrid
nanocomposites prepared by sol-gel technique.318-321 Figure 49a-b represents the TEM images of
ACM-silica system synthesized from 30 and 50 wt-% TEOS. In these cases, the TEOS/H2O mole
ratio had been kept at 1:2, reaction pH of 1-2 and all the samples had been gelled under the ambi-
ent condition. It was noticed from these figures that the average diameter of the silica particles
increased with increasing TEOS concentration (70 nm at 30 wt-% and, 100 nm at 50 wt-%).
436 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 49. — TEM images of (a) 30 wt-%; (b) 50 wt-%TEOS concentrations in ACM-silica.

Figure 50 demonstrates the tensile stress-strain plots of rubber-in situ silica hybrid nanocom-
posites synthesized by the sol-gel technique. The tensile strength and modulus gradually
increased with increasing TEOS (i.e. nanosilica) concentration as demonstrated through the
stress-strain plots on ACM-silica system in Figure 50.434,435

FIG. 50. — Tensile stress-strain plots for a ACM-silica hybrid nanocomposites prepared
by increasing TEOS concentration (number used in legends indicates wt.% of TEOS).

This was due to greater reinforcing action by the in situ generated silica nanoparticles, which
were almost uniformly dispersed within the rubber matrices. As a result, a maximum of 600%
increment in tensile strength over the control sample was achieved with 50 wt-% TEOS. It was
also observed that ordinary silica (precipitated silica) reinforced ACM composites gave a maxi-
mum of 180% increment in strength in comparison with the gum rubber specimen.435
The thermal properties of the rubber-silica hybrid nanocomposites have been investigated by
using a thermogravimetric analyzer (TGA). Figure 51 displays the representative differential
thermogravimetry (DTG) plots for ACM-silica hybrid nanocomposites with increasing TEOS
concentrations.436 For ACM-silica, all the hybrid nanocomposites display almost similar peak
degradation temperature values (Tmax at 406 °C) due to weak polymer-filler interaction.
 ELASTOMER NANOCOMPOSITES 437

FIG. 51. — DTG plots for ACM-silica (letter 'D' in legends indicates dicumyl peroxide
(DCP) crosslinked samples, number used in legends indicates wt.% of TEOS).

K. SILICONE RUBBER

Till date, very little work has been done on silicone rubber nanocomposites.437-441 Silicone
rubber-clay nanocomposites were synthesized by a melt-intercalation process using synthetic Fe-
montmorillonite and organically modified natural sodium montmorillonite by Kong et al.439 This
study was designed to determine if the presence of structural iron in the matrix could result in
radical trapping and then enhanced thermal stability and affected the crosslinking degree and
elongation. It was found that the iron acted as an antioxidant and radical's trap not only in ther-
mal degradation, but also in the vulcanization process. Novel room-temperature-vulcanized sili-
cone rubber/organo-montmorillonite nanocomposites were prepared by a solution intercalation
process by Wang et al.440 A new strategy was developed by Ma et al. to prepare disorderly exfo-
liated nanocomposites, in which a soft siloxane surfactant with a weight-average molecular
weight of 1900 was adopted to modify the clay.438
The physical and chemical aging of polysiloxane elastomers incorporating organo montmo-
rillonite nano-scale particles of differing dimensions and aspect ratios have been reported.442
Broadband dielectric spectroscopy (BDS) was employed to characterize the behavior of the filler
particles within the siloxane network by tracking changes in system ionic mobility and filler-
induced Maxwell-Wagner effects. TGA, DSC and sub-ambient thermal volatilization analysis
have provided degradative chemical information. The results indicated that the siloxane network
was undergoing a catalyzed rearrangement process leading to an increase in stability. BDS and
TGA data demonstrated that the process was influenced by the nano-filler.442
Flame-retardant methyl vinyl silicone rubber (MVMQ)/montmorillonite nanocomposites
were prepared by solution intercalation method, using magnesium hydroxide and red phospho-
rus as synergistic flame-retardant additives, and aero silica as synergistic reinforcement filler.443
The morphologies of the flame-retardant MVMQ/montmorillonite nanocomposites were charac-
terized by environmental SEM (ESEM), and the interlayer spacings were determined by small-
angle X-ray scattering (SAXS). In addition to mechanical measurements and limiting oxygen
index test, and thermal properties were tested. This kind of silicone rubber nanocomposite can
be a promising flame-retardant polymeric material.
A novel electrically conductive nanocomposite was successfully fabricated by dispersing
homogeneously conductive graphite nanosheets (GNs) in an insulating silicone rubber matrix.209
GN was prepared by powdering expanded graphite with sonication in aqueous alcoholic solution.
438 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

The particular geometry of GN, 30-80 nm in thickness with high aspect ratio, contributed to the
advantage of forming the conducting network, so that the percolation threshold of silicone rub-
ber/GN nanocomposite was about 0.009, much lower than that of composites with conventional
graphite.
The effects of γ-aminopropyltriethoxy silane coupling agent on electrical properties in mul-
tiwall carbon nanotube/methylvinyl silicone rubber nanocomposites were studied by Jiang et
al.444 The modified nanotubes could be dispersed homogeneously and that they had a tight bond-
ing with the rubber matrix. The concentration of coupling agent played a crucial role in deciding
the conductivity and the electrical properties of the nanocomposites exhibited strong depen-
dences on temperature and pressure. Dependences of electrical properties on temperature and
pressure were also improved by increasing the content of coupling agent. The thermal properties
of acid-treated multiwall carbon nanotube (MWNTs) dispersed in a silicon elastomer matrix
were described by Lee et al.445 The influence of the presence of static stress on the dynamic
mechanical properties of poly(dimethylsiloxane)-carbon nanotube composite was evaluated by
Paul et al.446 Significant enhancement in the dynamic stiffness was observed, which could be
attributed to the combined effect of nanotube nucleated strain induced crystallization, modula-
tion in the waviness of the nanotube entanglements, and the enhanced interfacial adhesion due
to the prevailing hydrostatic pressure. The study provided a platform for understanding the
behavior of carbon nanotube composites in the stressed state and thereby to consider the pre-
stressing process as an ideal option for enhancing the mechanical properties.
El-Hag et al. investigated the enhanced erosion resistance of silicone composites with fumed
silica (12 nm) as fillers. A laser based method was used as a source of heat to treat the filled and
unfilled samples of silicone rubber. Both the thermal and chemical bonding behavior were ana-
lyzed using AFM, TGA, FTIR spectra and thermal conductivity.447
The damage caused by 150 keV proton irradiation for two kinds of methyl silicone rubber,
including the silicone rubber reinforced with silicone resin (M-SR) and the silicone rubber mod-
ified with nano-TiO2 particles based on the M-SR rubber (T-SR), was studied using a space com-
bined irradiation simulator.448 In terms of the changes in surface morphology, mass loss and
mechanical properties, as well as microstructure, the resistance to proton irradiation of the T-SR
were evaluated.
Effect of metal particles like iron and silver was also investigated by numerous researchers
in silicone elastomers.210,449-451

L. EPICHLOROHYDRIN RUBBER

Polyepichlorohydrin. — Organically modified montmorillonite nanocomposites were pre-

pared by using dichloromethane as a co-solvent for both polymer and clay at room temperature,
through the solvent-casting method. The nanocomposites showed higher tensile modulus than
the polymer matrix.452
Nanocomposites of organophilic montmorillonite clay (OMMT) and polyepichlorohydrin
were prepared by a solvent-casting method using dichloromethane as a solvent.174 The interca-
lation of elastomer chains in the interlayers of the clay was confirmed by X-ray diffraction, and
the intercalation spacing was calculated. The increase in the onset temperature of the thermal
degradation indicated the enhancement of thermal stability of polyepichlorohydrin. Rheological
properties of the nanocomposites were investigated using a rotational rheometer in a steady shear
mode. The steady shear viscosity increased with the clay loading, and the shear thinning viscos-
ity data fitted well with the Carreau model. From the normalized shear viscosity analysis, a crit-
ical shear rate that is a crossover from a Newtonian plateau to a shear thinning region was found
to approximately equal the inverse of the characteristic time of the nanocomposites.174
 ELASTOMER NANOCOMPOSITES 439

M. FLUOROELASTOMERS

Very few reports are there on fluoroelastomer nanocomposites.453-455 Preliminary studies on

viscoelastic properties were done by Valsecchi et al.453 Kader and Nah reported the influence of
clay on the vulcanization kinetics of fluoroelastomer nanocomposites.455
Recently, Maiti and Bhowmick did extensive work on fluoroelastomer-clay nanocompos-
ites.33,172,272,285,456-458 They reported exciting results that a polar matrix like fluoroelastomer
(Viton B-50) was able to exfoliate unmodified clay (Cloisite NA+) as well as the modified one
(Cloisite 20A). The transmission electron micrographs also show that both the clays are exfoli-
ated in the matrix (Figure 52 a-b).

FIG. 52. — TEM micrograph of (a) unmodified and (b) modified clay filled nanocomposites.

They studied morphology, mechanical, dynamic mechanical and swelling properties of flu-
oroelastomer-nanocomposites. The unmodified clay filled systems showed better mechanical and
dynamic mechanical properties than the modified one (Figures 53 and 54).

FIG. 53. — Stress- strain curve of different nanocomposites based on Viton B-50 (vulcanized)
[FNA4-V = Viton B-50 + 4phr MMT (vulcanized), 30B = Cloisite 30B, 20A = Cloisite 20A].
440 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 54. — Variation of storage modulus with temperature for different nanocomposites.

The extraordinary results obtained with the unmodified clays were explained with the help
of thermodynamics and surface energetics. They explained it as follows:
The free energy change of the system after mixing the clay in fluoroelastomers may be given
as:

ΔGE = ΔHE – TΔSE, for elastomers (5)

ΔGC = ΔHC – TΔSC, for clays (6)

Therefore, total free energy change of the system is

ΔGS = ΔHS – TΔSS = ΔHS – T(ΔSE + ΔSC) (7)

From the expression, ΔGS value will be negative and hence the most favorable interaction
between the clay and the rubber will take place when ΔHS is negative and ΔSS is positive.
When polymer chains enter into the gallery of the clay, they reside in a restrained form, i.e.,
ΔSE is negative. In contrast, the expansion of the gallery by elastomer chains causes the entropy
change in the clay, ΔSC to be positive. If the clays are exfoliated, this may probably compensate
the entropy loss associated with the confinement of elastomer chains. Hence, in this condition,
negative ΔHS value makes ΔGS negative. They calculated ΔHS for different clay systems from the
IR spectra using Fowkes' equation, ΔHS= 0.236 × Δν. ΔHS was negative (-2.60 kcal/mol) for
unmodified clay based system. But for the modified clay filled samples, it was zero or has small
positive value. As a result, the mixing of the unmodified clay with the fluoroelastomer was more
favorable than that of the modified one.
The better interaction observed with the unmodified clay was also explained in terms of sur-
face energy. The values of surface energy of the fluoroelastomer and the clays, along with work
of adhesion, spreading coefficient and interfacial tension are reported in Table XI.
 ELASTOMER NANOCOMPOSITES 441

TABLE XI
DIFFERENT SURFACE PROPERTIES OF FLUOROELASTOMER AND CLAYS
Sample Work of Adhesion, Spreading Interfacial
mJ/m2 Coefficient, mJ/m2 Tension, mJ/m2
Fluoroelastomer 67.63 5.47 1.10
and Cloisite NA+
Fluoroelastomer 51.42 -9.91 2.47
and Cloisite 20A

The surface energy of unmodified clay (37.22 mJ/m2) was found to be higher than that of
fluorocarbon rubber (31.51 mJ/m2). Assuming fluoroelastomer as wetting polymer, its lower sur-
face energy helps in wetting the solid unmodified clay, following the Zisman approach. This was,
however, not the case with the fluoroelastomer -modified clay system, where the surface energy
of the modified clay (22.38 mJ/m2) was much lower. These results were obvious from the Δγ val-
ues. The Δγ value was much lower (5.71 mJ/m2) in the case of Viton B-50 and the unmodified
clay, than that (9.13 mJ/m2) of Viton B-50 and the modified clay. A lower surface energy mis-
match gave better wetting, better interfacial adhesion and increased diffusion of the polymers
across the interface. The interfacial tension between fluoroelastomer and the unmodified clay
was also much less. The positive spreading co-efficient for this system definitely indicated bet-
ter diffusion of the polymers into the clay interface. Hence, interaction was more in the case of
the unmodified clay. Besides, the work of adhesion was also higher in the case of the rubber-
unmodified clay system. Hence, the polymer chains could spread more easily on the surface of
the unmodified clay than that of the modified clay.
The mechanism of intercalation/exfoliation is responsible for physical property enhance-
ment of polymer-clay nanocomposite. It is widely accepted that the variability of interlayer spac-
ing occurs due to swelling of clay layers by intercalation of a wetting liquid, in the form of
organo modifier or the polymer itself.
Bhattacharya et al.130 proposed (Scheme 2) that the adsorption mechanism is equally impor-
tant, more so in case of clays having smaller gallery gaps and higher surface energy, for instance
sepiolite. The polymer, with sufficiently high Wa, first gets adsorbed on the surface of the clay
and tries to drag it away from the lattice during the process. Once sufficient gap is created, other
polymer chains intercalate into the inter layer spacing or channels. Subsequently, they push the
silicate layers further apart. This process is facilitated by the shear forces generated during mix-
ing either in solution or in the melt state. This mechanism of intercalation of clay by a polymer
can be termed as the adsorption-shear's mechanism (Scheme 2). The occurrence and extent of the
layer displacement was determined by the balance between the work of adhesion between the
polymer and clay and the cleavage energy of the clay layers.130

SCHEME 2. — Adsorption-Shear mechanism of polymer intercalation into clay gallery.

442 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

Maiti and Bhowmick also investigated the diffusion and sorption of methyl ethyl ketone and
tetrahydrofuran through fluoroelastomer-clay nanocomposites in the temperature range of 30-
60 °C by swelling experiments.457 A representative sorption-plot (i.e., mass uptake vs. square
root of time, t1/2) at 45 °C for all the nanocomposite-systems is given in Figure 55.

FIG. 55. — Sorption curves for different nanocomposites at 45 °C (solvent MEK)

[FNA4 = Viton B-50 + 4phr MMT (unvulcanized), NA = Cloisite NA, 20A = Cloisite 20A].

The transport mechanism had slight deviation from Fickian mode, as the sorption curves
were slightly sigmoidal. The overall sorption value decreased with the addition of the nanoclays
and was maximum for the unmodified clay filled sample, which also demonstrated the slowest
rate of increase of solvent uptake. As the temperature of swelling was increased, the penetrant
uptake increased in all the systems.
They also established a model to predict the aspect ratio of nanoclays from the swelling
studies. Addition of layered nanoclays to a neat polymer restricted the permeability
of nanocomposites (Pf) and reduced it from that of the neat polymer (P0) by the product of the
decreased area and the increased path length, as seen below:

P0 ⎛ A ⎞⎛ df ⎞
= ⎜ 0 ⎟⎜ ⎟
Pf ⎝ A f ⎠ ⎝ d0 ⎠ (8)

where A0 is the cross-sectional area available for diffusion in a neat polymer sample, Af the cross-
sectional area available for diffusion in a nanocomposite, d0 is the sample thickness (i.e. the dis-
tance a solvent molecule must travel to cross the neat polymer sample), df is the distance a sol-
vent molecule must travel to cross the nanocomposite sample.
Now,
V0
P0 d0 ⎛ df ⎞
= ⎜d ⎟
P f (
V −V 0 f )
⎝ ⎠ 0
(9)
df

where V0 is the total volume of the neat polymer sample and Vf is the volume of nanoclays in the
nanocomposite-sample.
 ELASTOMER NANOCOMPOSITES 443

2
P0 ⎛ df ⎞
V0
= (10)
Pf V0 − V f ⎜⎝ d0 ⎟⎠

2
1 ⎛ df ⎞
= (11)
1 − φ ⎜⎝ d0 ⎟⎠
where φ is the volume fraction of filler.
When a solvent diffuses across a neat polymer, it must travel the thickness of the sample
(d0). When the same solvent diffuses through a nanocomposite film with nanoclays, its path
length is increased by the distance it must travel around each clay layer it strikes. According to
Lan et al.459 the path length of a gas molecule diffusing through an exfoliated nanocomposite is

d0 Lφ (12),
d f = d0 + 2 dc

where L and dc are the length and thickness of a clay layer, respectively.
Substituting this value in Equation 11,

P0 1 ⎛ Lφ ⎞
= ⎜ 1+ (13)
Pf 1− φ ⎝ 2 dc ⎟⎠

1 ⎛ αφ ⎞
= 1+ (14)
1− φ ⎝ 2 ⎠
L
=α
dc
where, aspect ratio,

The aspect ratio of the nanoclays in different samples were calculated using Equation 14 and
is reported in Table XII. These values corroborated with those inferred from image analysis of
TEM images.

TABLE XII
AVERAGE ASPECT RATIO OF CLAY LAYERS PRESENT IN DIFFERENT NANOCOMPOSITES
Sample Aspect Ratio Morphology
Swelling
FNA4 146±14 145±6
F20A4 63±5 53±6

Maiti and Bhowmick also investigated the effect of synthetic montmorillonite on the prop-
erties of fluoroelastomers.33 The plot in Figure 56 shows the comparison of mechanical proper-
ties of various nanocomposites. The natural montmorillonite filled sample [FNA4] showed 65
and 51% improvement in tensile strength and 100% modulus respectively over the control (F).
All the synthetic clay filled samples [FSM-A4, FSM-D4, FSM-E4, FSM-A8] provided better
tensile strength compared to natural clay filled one. FSM-A4 showed 159 and 58% increment in
tensile strength and 100% modulus compared to the control. Better swelling and thermal resist-
444 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

ance were also demonstrated by the synthetic clay based nanocomposites. Synthetic clay based
nanocomposites were observed to be thermodynamically more favorable than the natural clay
filled one.

FIG. 56. — Comparison of physico-mechanical properties of different montmorillonite-like

layered silicate based nanocomposites ( SM-A, B,C,D,E are different synthetic MMT;
FSM-A4 is 4 phr SM-A filled fluoroelastomer nanocomposite).

N. POLYURETHANE (PU)

Preparation, characterization, mechanical and barrier properties, morphology and effect of

processing conditions have been reported on polyurethane based clay- nanocomposites.460-471
Marchant et al.470 showed that the coefficient of thermal expansion of polyurethane elastomers
increased by 85% with the addition of 10 wt.% of nano-clay, and by 98% with 15 wt.% of car-
bon nano fibers. Rehab and Salahuddin synthesized polyurethane organoclay nanocomposites
via in situ polymerization method.468
A polyurethane/multi-walled carbon nanotube elastomer composite was synthesized by
Xiong et al.472 The chemical linkage of carbon nanotubes with polyurethane matrix was con-
firmed by FTIR spectra. The carbon nanotubes could be dispersed in the polymer matrix well
apart from a few of clusters. Glass transition temperature of the composite was increased by
about 10 °C and its thermal stability was obviously improved, in comparison with pure
polyurethane. The investigation on the mechanical properties showed that the modulus and ten-
sile strength could be obviously increased by addition of 2-wt% CNT to the matrix.
The study by Guiffard et al. dealt with the improvement of electric field-induced thickness
strain of polyurethane elastomer films by carbon black nanopowder (C) incorporation in the
polymer matrix.473 Different carbon volume concentrations were tested. Weak-field dielectric
and resistivity measurements revealed that a percolative effect was not induced by carbon filling
up to 1.5 vol%. Thickness strain measurements showed that both pure PU and C/PU composite
films exhibited similar strain variations, which were not governed only by electrostatic forces
and/or electrostriction forces. The highest strain amplitude value was obtained for 1% C com-
posite thin film.
Novel thermoplastic polyurethane (TPU) was derived from -NCO terminated polyurethane
prepolymer and hyperbranched polyester polymer (HPB) and the effect of layered silicate was
studied by Maji et al.474 An apparent microphase-segregated morphology of the pristine polymer
and its nanocomposites was observed by transmission electron microscopy (TEM) and atomic
force microscopy (AFM) with regions of exfoliation and intercalation confirmed by X-ray dif-
fraction (XRD) analysis. The nanocomposite containing 8 wt% clay loading showed remarkable
 ELASTOMER NANOCOMPOSITES 445

increase in tensile and peel strength, while helium gas permeability decreased by around 70%.
Dramatic improvements in thermal and dynamic mechanical properties over the control TPU
were also observed. Fourier transform infrared spectroscopy analysis indicated that the extent of
tethering reactions between the polymer chains carrying residual -NCO groups and the reactive
HPB was significant and the nanofiller reacted mostly with -NCO containing prepolymer.474
Pattanayak and Jana synthesized and studied the properties of bulk-polymerized thermo-
plastic polyurethane nanocomposites.475,476 Jana and co-workers have also investigated the effect
of incorporation of nanoclay in different polyurethanes477,478 and observed the manifestation of
unique shape memory effects in such nanoclay-tethered polyurethane nanocomposites.478

O. THERMOPLASTIC ELASTOMERS

Thermoplastic elastomer (TPE)-clay nanocomposites based on poly[styrene-(ethylene-co-

butylene)-styrene] triblock copolymer (SEBS) and poly[styrene-butadiene-styrene] triblock
copolymer (SBS) were prepared by various workers using natural sodium montmorillonite and
different organically modified nanoclays.479-484 Mechanical, dynamic mechanical properties and
morphology of these nanocomposites were also studied by Ganguly et al.273 Modified clay
showed better properties than the unmodified one. They also compared two processing tech-
niques namely, solution and melt blending. With atomic force microscopy (AFM) they showed
distinctly different morphologies in nanocomposites prepared through solution and melt pro-
cessing. Extensive morphological investigations were also done by Ganguly et al. using AFM.273
The lamellar thickness of the soft phases of SEBS was widened in nanocomposites, where the
layered clay silicates were embedded in the soft rubbery phases in the block copolymeric matrix
of the nanocomposite (shown in Figure 57).

FIG. 57. — Tapping mode phase morphology of the nanocomposites (a) SEBS-Cloisite 20A and (b) its 3D image.

As discussed earlier, qualitative and quantitative investigation of surface forces of interac-

tion for the neat SEBS and its nanocomposite measured at constituting blocks and clay regions
by force distance and force volume plots was also done by the same workers. Maximum adhe-
sive force of 25 nN was found in rubbery poly(ethylene-co-butylene) segments and cantilever
deflection was found to be maximum (210 nm) for clay regions both in single point force map-
ping and entire force volume force mapping of SEBS-clay nanocomposite under investigation
(Figure 58).273
446 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

FIG. 58. — Forces of interactions on blocks and nanoclay of SEBS-clay nanocomposite

taken from force volume experiments.

The same research group functionalized SEBS at the mid-block by means of chemical graft-
ing by two polar moieties - acrylic acid and maleic anhydride and subsequently synthesized
nanocomposites based on hydrophilic MMT clay at very low loadings.485 The mid-block was
grafted with 3 and 6 weight % acrylic acid through solution grafting and 2 and 4 wt% maleic
anhydride though melt grafting reactions which were confirmed by spectroscopic techniques.
The nanocomposites derived from the grafted SEBS and MMT clay conferred dramatically bet-
ter mechanical, dynamic mechanical and thermal properties as compared to those of SEBS and
its clay based nanocomposites. The morphology also changed with modification. SEBS with 4
phr MMT nanocomposites showed agglomerated microstructure while acrylated and maleated
SEBS with same amount of MMT, exhibited exfoliation and exfoliation-intercalation respective-
ly (Figure 59 a-c).

FIG. 59. — TEM micrographs of (a) agglomerated SEBS-4phr MMT, (b) exfoliated acrylated
SEBS-4phr MMT and (c) intercalated- exfoliated mixed maleated-SEBS-4phr MMT.
 ELASTOMER NANOCOMPOSITES 447

Phillips et al. measured nano-tack using AFM and bulk-tack adhesive forces of blends of
C60 fullerene sensitizer with poly[styrene-butadiene-styrene] (SBS) and poly[styrene-isoprene-
styrene] (SIS) triblock copolymer pressure sensitive adhesives after exposure to visible light irra-
diation. C60 fullerene sensitizer - in the presence of visible light and molecular oxygen - gener-
ated singlet oxygen, which was likely responsible for the irreversible oxidative crosslinking of
SIS and SBS polymers and subsequent loss in adhesion.486
Star-shaped and linear block thermoplastic poly(styrene-b-butadiene) copolymer
(SBS)/organophilic montmorillonite clays (OMMT) were prepared by a solution approach by
Liao et al.487 The mechanical strength of nanocomposites with the star-shaped SBS/OMMT were
significantly increased.
The morphology and mechanical behavior of poly[styrene-b-(maleated ethylene/butylenes)-
b-styrene] (mSEBS) and their nanocomposites were studied using transmission electron micro-
scope (TEM) and mechanical testing system. The mechanical properties of these nanocompos-
ites were tailored through selective incorporation of silicate or organically modified silicate via
domain-targeted in-situ sol-gel reactions.488
Magnetic nanoparticles were created in or around the sulfonated polystyrene domains in a
poly(styrene-ethylene-butylene) block copolymer using an in situ inorganic precipitation proce-
dure. The sulfonated block copolymer was neutralized with a mixed iron/cobalt chloride elec-
trolyte, and the doped samples were converted to their oxides by reaction with sodium hydrox-
ide. These nanocomposites were shown, using alternating gradient magnetometry, to be ferri-
magnetic at room temperature.489
TPE-clay nanocomposites based on rubber-plastic blends such as Engage(EN)-
Polypropylene (PP), Nylon 6-BIMS, EPDM-PP, EVA- Styrene- acrylonitrile copolymer (SAN),
polyamide 6-maleated SEBS, PP-SEBS, polyamide 6-silicone rubber were reported by different
researchers.490-495 Maiti et al. studied the structure-property relationship of EN-PP and Nylon 6-
BIMS-clay nanocomposites.490 They prepared the nanocomposites by making masterbatch of
clay either with rubber phase or plastic phase, followed by blending them. The dynamic mechan-
ical properties of different nanocomposites are reported in Table XIII. Rubber /clay masterbatch,
ENOC4/PP, showed higher storage modulus compared to the corresponding plastic/clay coun-
terpart of EN/PPOC4, which was in line with the tensile properties. The modulus at 100% elon-
gation was also higher in the case of ENOC4/PP than that of EN/PPOC4.

TABLE XIII
DYNAMIC MECHANICAL PROPERTIES OF THE ENGAGE®-POLYPROPYLENE BLENDS
Sample Tg, °C Tan Delta Log E' at Log E' at
Name at Tg 25 °C 70 °C
(MPa) (MPa)
EN -55 0.33 6.05 5.87
EN/PP -51 0.24 6.70 6.23
ENOC4/PP - 0.18 7.23 6.81
EN/PPOC4 -51 0.22 7.31 6.40

Patel et al. showed that MMT provided better improvement in physical properties like ten-
sile strength, tension set, and modulus than OMMT in EVA-SAN TPE blends.491
The effects of dynamic vulcanization on the morphology and rheology of EPDM/PP ther-
moplastic vulcanizates (TPVs) and their nanocomposites were also studied.494 It was shown that
a TPV nanocomposite generated interesting properties that significantly depended on the phase
location of the silicate nano clay - whether it lied in the dispersed rubber phase or in the contin-
448 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

uous plastic matrix. Frounchi et al. studied the gas barrier properties of PP/EPDM blend
nanocomposites.495 Effect of sepiolite clay on the properties of TPEs [ethylene-butene copoly-
mer and LDPE blend] was studied by Tembhekar et al.496 Sepiolite clay dispersed within the TPE
to prepare the nanocomposites which were characterized by TEM. The TEM study displayed a
combination of intercalation and exfoliation of the clays, as the width of the discrete clay parti-
cles is in the range 20-30nm. The nanocomposites from different TPEs showed significant
improvement in mechanical properties.496 The effect of nanosilica and nanoclay on EPDM/PP
blend was also investigated by Chakraborty et al.497

VIII. COMPARISON BETWEEN PROPERTIES OF CONVENTIONAL AND

NANOFILLER FILLED RUBBER COMPOSITES
Bhattacharya et al. studied a wide gamut of fillers at the same loading (4phr) in SBR130 and
NR136 to understand and compare the reinforcing effects of these fillers at a critical loading
which derived the best set of properties from nanofillers like nanoclays and nanofibers. Their
observation in SBR nanocomposite has been summarized in Table XIV. The results indicated that
modified organoclays and carbon nanofiber yielded the best results at 4 phr loading, while the
unmodified clays (RD and H) gave the poorest properties. Conventional fillers like, silica and
carbon black measured up in between these two sets of fillers in terms of 300% modulus, tensile
and tear strength.130 Similar results were demonstrated by the corresponding NR systems, as
well.136

TABLE XIV
MECHANICAL PROPERTIES & CROSSLINK DENSITY OF SBR GUM AND NANOCOMPOSITES AT 4PHR LOADING
Sample 300% Modulus T.S. (MPa) Tear (N/mm) Crosslink density,
(MPa) 1/2Mc X 104
(mol/cc of RHC a))
S 2.15±0.06 b) 2.78±0.21 13.90±0.85 1.90
S RD 4 1.59±0.05 1.59±0.14 11.43±0.23 1.56
S H4 1.61±0.13 1.84±0.08 13.00±1.23 1.82
S NA4 3.22±0.26 3.79±0.09 13.10±0.65 1.69
S 15A4 3.18±0.03 6.48±0.34 18.23±0.21 2.28
S SP4 2.96±0.09 3.55±0.05 18.85±0.55 2.26
S SI4 1.83±0.06 2.43±0.17 13.85±1.16 1.70
S G4 2.58±0.19 3.17±0.16 15.90±0.42 2.27
S B4 2.24±0.01 2.86±0.18 16.60±0.64 1.94
S F4 - 3.37±0.02 26.55±1.63 2.37
a)RHC = rubber hydrocarbon; b) Standard Deviation; S: SBR; RD: Laponite RD; H: Hectorite; NA: Cloisite NA; 15A:
Cloisite 15A; SP: Sepiolite; SI: Colloidal Silica; G: Expanded Graphite; B: N330 Carbon Black; F: VGCNF; 4 stands for
4 phr loading.

Lamba498 reported that tensile strength was improved 5 fold in 40% styrene containing SBR-
clay nanocomposites on addition of 4phr of clays, while the tear strength of 20 wt% nanoclay
filled EPDM depicted up to 200% improvement. Gas permeation of O2 at room temperature got
reduced by 60% with 10 phr of nano-clays in EPDM. Electrical properties were investigated on
a proprietary wire and cable EPDM compound, and viscosity measurements correspond to pro-
prietary NBR compounds filled with classical filler and carbon nanotubes, as well.The corre-
sponding black (classical) composites were also studied and the Figure 60 shows the compara-
 ELASTOMER NANOCOMPOSITES 449

tive study between classical filler and nanofiller filled composites at the same loading. The much
superior performance of the nanocomposites is clearly reflected in terms of the change in prop-
erty improvement percentage.

FIG. 60. — Comparative study between (a) classical fillers and nanoclay, and
(b) classical fillers and carbon nanotube filled composites at the same loading.

Bandyopadhyay et al.435 made similar comparative studies on the properties of convention-

al and nanosilica, albeit at much higher loading. Nano silica was found to show remarkably bet-
ter properties, in comparison to the conventional counter part at every loading (Figure 61).

FIG. 61. — Comparative plots of tensile strength between nanosilica and

precipitated silica reinforced uncrosslinked ACM composite.

IX. THEORIES/MODELING IN THE FIELD OF RUBBER NANOCOMPOSITES

Polymer nanocomposites offer a wide range of promising applications by virtue of rein-
forcement by nanoparticles. However, multiscale modeling and simulation strategies need to
evolve further for the fundamental understanding of their hierarchical structures and behaviors
450 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

necessary for development of such nanomaterials. Here, we discuss some of the computational
and numerical methods that have been applied to polymer nanocomposites.
Till date, some theoretical efforts have addressed the structural changes of polymer chains
due to the addition of spherical nanoparticles. The variables like particle size, particle loading,
chain length and particle-polymer interaction strength have been studied. Sharaf and co-work-
ers499-501 found that the volume fraction and/or the size of nanoparticles as well as their spatial
arrangement in a polymer matrix significantly affect the end-to-end chain distance. Buxton and
Balazs502 used lattice spring model to investigate the effects of filler geometry and intercalation-
exfoliation of clay platelets. Their simulations showed that polymers filled with platelets demon-
strate the most significant increase in reinforcement efficiency with incomplete exfoliation of
clay platelets leading to a less effective reinforcement, while those filled with spheres have the
lowest reinforcement efficiency. They attributed the reinforcement efficiency to the volume of
polymer matrix constrained in the proximity of the particles.
In order to understand the effects of filler loading and filler-filler interaction strength on the
viscoelastic behavior, Chabert et al.503 proposed two micromechanical models (a self-consistent
scheme and a discrete model) to account for the short range interactions between fillers, which
lead to a good agreement with the experimental results. The effect of the filler-filler interactions
on the viscoelasticity of filled cross-linked rubber was studied by Raos et al.504 via Dissipative
Particle Dynamics (DPD) simulation. They examined such effect in systems having dispersed,
moderately aggregated, and fully aggregated filler particles and observed that filler-filler inter-
actions have a clear effect on the dynamic shear modulus.
The effect of polymer-filler interaction on solvent swelling and dynamic mechanical prop-
erties of the sol-gel derived acrylic rubber (ACM)/silica, epoxidized natural rubber (ENR)/silica,
and poly (vinyl alcohol) (PVA)/silica hybrid nanocomposites was described by Bandyopadhyay
et al.317 The storage modulus dropped at higher strain (>1%), which indicated disengagement of
polymer segments from the filler surfaces. It also showed sharp increase with increasing fre-
quency at a fixed strain level (0.1%).
The variation of ΔE' at a particular frequency and at constant strain in the hybrid nanocom-
posites against the volume fraction (ϕ) of the silica is shown in Figure 62a and Figure 62b,
respectively. For the strain sweep, the drop in modulus with theoretical volume fraction of silica
(θ) was interpreted with the help of a Power law model , where a1 was a const. and b1
was primarily a filler attachment parameter.
In the case of frequency sweep, the increase in modulus with θ also followed similar model
proposed in the strain sweep mode. This is displayed in Figure 62b. In this case, the
constant "a2" is 0.25.
 ELASTOMER NANOCOMPOSITES 451

FIG. 62. — Plots of ΔE' vs. theoretical volume fraction of silica in the hybrid
nanocomposites calculated from (a) strain sweep, and (b) frequency sweep mode.

The magnitude of "b1" in ACM/ silica, ENR/ silica and PVA/ silica hybrid nanocomposites
is recorded in Table XV.

TABLE XV
SOLVENT SWELLING AND POLYMER-FILLER INTEGRATION DATA OF THE HYBRID NANOCOMPOSITIES
Nanocomposite Slope (m) Kraus b1 -b2
series Constant (C) from strain from frequency
sweep mode sweep mode
ACM/ silica -1.63 1.85 0.011a 0.45a
0.003b
ENR/ silica -2.06 2.30 0.150a 0.24a
0.125b
PVA/ silica -3.15 3.53 0.210a 0.09a
0.178b
a = The data corresponding to 500 °C; b = The data corresponding to 700 °C.

Different levels of interaction of the polymers (ACM, ENR and PVA) with nanosilica are
delineated by the parameter "b1". Highest "b1" value for PVA and least for ACM at the experi-
mental temperatures (50 and 70 °C) with almost similar silica concentration was attributed to
higher concentration of interactive OH groups in the former, which undergo hydrogen bond for-
mation with the silanol groups of silica. The magnitude of "b1" which is a strong function of ΔE'
is in fraction in all the nanocomposite systems.
Variation of ΔE' with ϕ in the similar fashion implies an identical correlation between the
responses obtained from these two different modes (strain and frequency sweeps). The effective
interaction at the organic-inorganic interface is responsible for this trend.
Wu et al.337 verified the modulus reinforcement of rubber-clay nanocomposites using com-
posite theories based on Guth, Halpin-Tsai and the modified Halpin-Tsai equations. On intro-
duction of a modulus reduction factor for the platelet-like fillers, the predicted moduli were
found to be closer to the experimental measurements.
Bhattacharya and Bhowmick505 quantified the polymer-filler interaction for nanocomposites
by introducing Interface Area Function (IAF), to account for the nanofiller characteristics com-
452 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

prising of the specific surface area, correlation length and the filler volume fraction. IAF sup-
plants the immeasurable filler characteristic terms, rendering tractability to the equation derived
by considering the restraining forces acting on a nanofiller- elliptical platelet- embedded in rub-
ber matrix. However, neglecting such terms reduces the same to the Kraus' equation.
Recognition of the due importance of such filler characteristics, by introduction of IAF,
resulted in better fitment of swelling data and also conformance with the trend predicted by
Zisman’s interpretation of surface energy. Experimental values of Young’s modulus of natural
and styrene-butadiene rubber nanocomposites and those predicted by of simple composite mod-
els, for instance the Guth-Gold equation, conform post introduction of IAF, with mere 5-20%
deviations (Figure 63). On the other hand, the pre-incorporation of shape related factors in the
IAF caused a multiplicative term to be carried through in the case of modified Guth-Gold and
Halpin-Tsai equations. Since these equations already had shape related correction introduced (to
address rod like fillers, instead of spherical fillers) the inclusion of IAF resulted in gross over
estimation, especially at higher loadings of nanofillers with high specific surface areas (Figure
63).
Since the IAF suitably integrated the shape and aggregate effects in polymer nanocompos-
ites, it was applied to tailor the Halpin-Tsai equation into much simpler forms for polymer
nanocomposites comprising of matrix-filler combinations having extremely large difference in
Young's moduli.
Halpin-Tsai equation has a term α, raised to the power of one, to accommodate the filler
aspect ratio. Since Interface Area Function (IAF) intended to supplant the same, the new equa-
tion was expected to have a reduced dependence on the aspect ratio. This understanding was sub-
jected to test by sequentially diluting the presence of aspect ratio in the equation. The first mod-
ified Halpin-Tsai equation, contained a correction term in the form of a shape reduction factor
(α0.5), Equation 15, while the second modified Halpin-Tsai equation, Equation 16, was devoid of
any extra shape related corrections.

⎧1 + α 0.5 ψφ ⎫
modified Halpin-Tsai I, E = Em ⎨ ⎬ (15)
⎩ 1 − ψφ ⎭
and
⎧1 + ψφ ⎫
modified Halpin-Tsai II, E = Em ⎨ ⎬ (16)
⎩1 − ψφ ⎭
Figure 63 illustrates that unlike original Halpin-Tsai equations, these were able to predict the
composite's Young's modulus within acceptable limits, which further underlined the necessity of
inclusion of IAF and the justification in choosing its constituents.
 ELASTOMER NANOCOMPOSITES 453

FIG. 63. — Fitment of composite models on introduction of IAF, for Cloisite 15A in NR.

The combined molecular dynamics (MD) and continuum models (e.g., FEM, Mori-Tanaka,
Halpin-Tsai) have been used to predict the dependence of the stiffness of clay-based polymer
nanocomposite on clay content by Sheng et al.506
Based on the concept of effective particle, they employed various continuum models to cal-
culate the overall elastic modulus of polymer-clay nanocomposites and their dependence on the
polymer matrix and clay properties as well as internal clay structural parameters. The combined
model could capture the strong modulus enhancements observed in clay-based elastomer
nanocomposites and were in good agreement with experimental data.
The observable properties of the polymer nanocomposite materials depend on a hierarchy of
structure involving atomistic chemical details, microscopic features of chains and clusters of clay
platelets and macroscopic continuum phenomena. From this point of view, new strategies for
multiscale modeling and simulation are essential to predict accurately the physical/chemical
properties and material behavior which links the methods from microscale to mesoscale and
macroscale levels.507

X. HEALTH AND SAFETY ASPECTS OF NANOPARTICLES/ NANOCOMPOSITES

Until recently, nanoparticles were widely accepted as beneficial and totally benign. But with
the astonishing revelation in March 2002 that nanoparticles are showing up in the livers of
research animals, can seep into living cells, and perhaps associated with bacteria to enter the food
chain, concerns have been raised about potential health and environmental impacts of nanoma-
terials.508
Almost all concerns have related to free, rather than fixed nanomaterials. There has been lit-
tle research into the potential hazards (health, safety and environmental effects) of these materi-
als, their exposure, persistence or the risks to people or the environment exposed to them.
However, the volume of data is increasing, as more organizations work on the health and envi-
ronmental aspects of nanomaterials. For example, there is a great deal of ongoing research into
nanoscale metal oxides, carbon nanotubes, fullerenes and quantum dots.509-512
The same properties that nanomaterials are designed to exhibit are also properties that may
cause nanomaterials to present human health and environmental hazards. For example, with
decreasing particle size, the surface area to mass ratio becomes greater. This means that there are
potentially more atoms on the surface to react with the environment and other substances. High
454 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

reactivity is a desired property for many intended applications of nanomaterials, such as cata-
lysts; however, this increased reactivity can lead to greater toxicity for cells and living organisms.
The influences of physicochemical properties on the toxicological and eco-toxicological profile
of nanomaterials are not yet fully understood.
Limited data from preliminary studies in experimental animals have shown that some nano-
materials can accumulate in the lungs and translocate to the blood, cross the blood-brain barrier,
and produce inflammatory responses and are capable of direct interaction with DNA in vitro.
Parallels have also been drawn with the incidentally produced nanoparticles (such as ultrafine
particles in diesel exhaust and other combustion products) and their associated adverse health
effects. To date, there have been no confirmed reports of adverse effects to humans or the envi-
ronment as a result of exposure to engineered nanomaterials.513-516
Factors determining human and environmental exposure include the extent of use, the expo-
sure pathway and properties of the nanomaterial. There is potential for exposure to humans and
the environment during manufacture, use and disposal of nanomaterials, but it is difficult to iden-
tify and quantify right now.
Despite recent findings of potential risks related to nanotechnology, and also the fact that
governments worldwide are spending billions of dollars to encourage commercial scale
nanobusiness, there is no regulatory body dedicated to control this potent and powerfully inva-
sive new technology.517,518 Industry and academics are now facing the challenge to develop a
conceptual understanding of biological responses to nanomaterials, and use this know-how to
develop safe nanomaterials. Only combining know-how on material properties, size and quan-
tum effects of anticipated products and an expertise on biological reactions to materials, will lead
to safe, sustainable applications of nanomaterials.

XI. APPLICATIONS
Though, elastomer nanocomposites have witnessed very little commercialization, the plau-
sible applications of such nanocomposites are tremendous. In applications where a light weight
but high strength elastomer product is of great significance, such as in space-shuttles, substitu-
tion of conventional fillers (carbon black and silica) by nanofillers may be highly desirable.
Superior barrier properties given by the platy/flake type nanofillers like, clay, applications
demanding low solvent and/or vapor permeability will always have scopes for nanocomposites.
Thus, in near future tire inner liners can be made of nanocomposites.
As the silicate type of nanofillers can enhance the flame and fire retardancy of elastomers,
cable jacketing elastomer compounds can contain nanoclays.
The zinc compounds are ecotoxic. Using nano ZnO, we can reduce the loading of such zinc
compounds and thus reduce the extent of ecotoxicity of such rubber compounds.
Although little information is available on already commercialized rubber nanocomposite
products, the field of thermoplastic nanocomposites has seen some rapid growth and has already
established a niche for themselves in the global consumer market. Some of the well known com-
mercial thermoplastic nanocomposite materials, along with their key features, applications and
manufacturer are listed below in Table XVI.519
 ELASTOMER NANOCOMPOSITES 455

TABLE XVI
COMMERCIALIZED NANOCOMPOSITES
Product Characteristics Applications Producer
Nylon Improved modulus, Automotive parts Bayer, Honeywell,
nanocomposites strength,heat distort (e.g. timing belt cover, Polymer RTP Company,
temperature,barrier engine cover,barrier, fuel Toyota Ube Unitika
properties line),packaging, barrier film

Polyolefin Stiffer, stronger, less brittle, Step-assist for GMC Safari Basell, Blackhawk
nanocomposites lighter, more easily recycled, and Chevrolet Astro vans, Automotive, Plastics Inc,
improved flame retardancy heavy-duty electrical General Motors,
enclosure Gitto Global
Corporation,
Southern Clay Products

M9 High barrier properties Juice or beer bottles, Mitsubishi Gas

multi-layer films, Chemical Company
containers

Durethan KU2-2601 Doubling of stiffness, high Barrier films, Bayer

(nylon 6) gloss and clarity, reduced paper coating
oxygen transmission rate,
improved barrier properties

Aegis NC (nylon Doubling of stiffness, Medium barrier Honeywell Polymer

6/barrier nylon) higher heat distort bottles and films
temperature, improved
clarity

Aegis TM OX Highly reduced oxygen High barrier Honeywell Polymer

transmission rate, beer bottles
improved clarity

Forte nanocomposite Improved temperature Automotive furniture Noble Polymer

resistance and stiffness, appliance
very good impact
properties

XII. CONCLUSIONS
Several examples of elastomer nanocomposites with different nanofillers have been pre-
sented in this article. Nanocomposite preparation with various fillers has also been discussed.
Existing theories and models for understanding the properties of nanocomposites have been
explored.
In a nutshell, the resulting nanocomposites possess several advantages:
(a) They generally exhibit improved mechanical properties compared to conventional com-
posites.
456 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

(b) They exhibit a remarkable increase in thermal stability, as well as self-extinguishing

characteristics for flammability.
(c) They show many fold reduction in the permeability of gases due to the formation of a
'tortuous path' in the presence of high aspect ratio impermeable fillers in the nanocom-
posites.
These improved properties are achieved at lower filler content (<10 wt%) compared to that
of conventionally filled systems. For these reasons, nanocomposites are far lighter in weight than
conventional composites, and make them competitive with other materials for specific applica-
tions.
Although a significant amount of work has already been done on various aspects of
nanocomposites, much research still remains in order to understand the complex structure-prop-
erty relationships in various nanocomposites. Though an attempt to address the health and envi-
ronmental safety issues has been taken in this review, there is yet lot more to be done in this field.

XIII. REFERENCES
1T. J. Pinnavaia, and G. W. Beall, "Polymer-Clay Nanocomposites," John Wiley & Sons, New York, 2000.
2R. Krishnamoorti, and R.A.Vaia, Polymer Nanocomposites: Synthesis, Characterization and Modeling, ACS
Symposium Series, 804; American Chemical Society, Washington, DC, 2002.
3G. O. Shonaike, and S. G. Advani, "Advanced Polymeric Materials: Structure Property Relationships," CRC Press, Boca
Raton, FL, 2003.
4P. M. Ajayan, L. S. Schadler, and P. V. Braun, "Nanocomposite Science and Technology," Wiley-VCH, Weinheim, 2003.
5E. P. Giannelis, Adv. Mater. 8, 29 (1996).
6S. Sinha Ray, and M. Okamoto, Prog. Polym. Sci. 28, 1539 (2003).
7M. Alexandre, and P. Dubois, Mater. Sci. Eng. 28, 1 (2000).
8P. C. LeBaron, Z. Wang, and T. J. Pinnavaia, Appl. Clay Sci. 15, 11 (1999).
9K. Friedrich, S. Fakirov, Z. Zhang, "Polymer Composites:From Nano-to Macro-Scale," Springer, New York, 2005.
10J. A. Schwarz, C. I. Contescu, and K. Putyera, "Dekker Encyclopedia of Nanoscience and Nanotechnology," Marcel
Dekker, New York, 2004.
11O. Becker, "Inorganic Polymeric Nanocomposites and Membranes," Springer, New York, 2005.
12J. H. Koo, "Polymer Nanocomposites: Processing, Characterization, and Applications," McGraw-Hill, New York, 2006.
13J. K. Kocsis, and C. M. Wu, Polym. Eng. Sci. 44, 1083 (2004).
14Q. H. Zeng, A. B. Yu, G. Q. Lu, and D.R. Paul, J. Nanosci. Nanotech. 5, 1574 (2005).
15S. C. Tjong, Mater. Sci. Eng. R: Reports 53, 73 (2006).
16O. Gryshchuk, and J. Karger-Kocsis, J. Nanosci. and Nanotech. 6, 345 (2006).
17P. D. Calvert, Mater. Res. Soc. Bull. 17, 37 (1992).
18J. Wen, and G. L.Wilkes, Chem. Mater. 8, 1667 (1996).
19J. L. Noell, G. L. Wilkes, and D. K. Mohanty, J. Appl. Polym. Sci. 40, 1177 (1990).
20R. H. Lee, G. H. Hsiue, and R. J. Jeng, J. Appl. Polym. Sci. 79, 1852 (2001).
21M. Morton, "Rubber Technology," van Nostrand, New York, 1973.
22C. M. Blow, and C. Hepburn, "Rubber Technology Manufacturing," Butterworths Scientific, London, 1982.
23J. E. Mark, B. Erman, and F. R. Eirich, "Science and Technology of Rubber," Elsevier, Amsterdam, 3rd Edition, 2005.
24L. A. Goettler, and W. F. Cole, in "Handbook of Elastomers," A. K. Bhowmick, and H. L. Stephens, Eds., 2nd Edition,
Marcel Dekker Inc., New York, 2001.
25D. Hull, and T. W. Clyne, "An Introduction to Composite Materials," Cambridge University Press, 2nd Edition,
London, 2003.
26R. Rothon, Adv. Polym. Sci. 139, 67 (1999).
 ELASTOMER NANOCOMPOSITES 457

27Y. Kojima, A. Usuki, M. Kawasumi, A. Okada, Y. Fukushima, T. Kurauchi, and O. Kamigaito, J. Mater. Res. 8, 1185
(1993).
28A. Usuki, Y. Kojima, M. Kawasumi, A. Okada, Y.Fukushima, T. Kurauchi, and O. Kamigaito, J. Mater. Res. 8, 1179
(1993).
29http://mineral.galleries.com/minerals/silicate/clays.htm, access date 9.8.2004.
30G. W. Brindley, and G. Brown, "Crystal Structures of Clay Minerals and Their X-Ray Indentification," Mineralogical
Society, London, 1980.
31R. Grim, "Clay Mineralogy," Mcgraw Hill, NY, 1968.
32D. F. Schmidt, "Polysiloxane/Layered Silicate Nanocomposites: Synthesis, Characterization, and Properties," Ph. D.
Thesis, Cornell University, NY, May, 2003.
33M. Maiti, and A. K. Bhowmick, Comp. Sci. and Tech. 68, 1 (2008).
34G. Lagaly, Clay Minerals 16, 1 (1981).
35A.T.Perkins, Soil Science 74, 443 (1952).
36J. Pleysier, and A.Cremers, Farad. Trans. 71, 256 (1975).
37A. Okada, Kobunshi 42, 589 (1993).
38N. Hasegawa, M. Kawasumi, M. Kato, A. Usuki, and A. Okada, J. Appl. Polym. Sci. 67, 87 (1998).
39A. Hartwig, and D. Puetz, (for Fraunhofer IFAM) German Patent, DE 10353890, June 23, 2005.
40J. Zhu, and C. A. Wilike, Chem. Mater. 13, 4649 (2003).
41Q. Zhang, Q. Fu, L. Jiang, and Y. Lei, Polym. Int. 49, 1561 (2000).
42S. Ray, and A. K. Bhowmick, RUBBER CHEM. TECHNOL. 74, 835 (2001).
43S. Sadhu, and A. K. Bhowmick, RUBBER CHEM. TECHNOL. 76, 860 (2003).
44E. Manias, H. Chen, R. Krishnamoorti, J. Genzer, E. J. Kramer, and E. P. Giannelis, Macromolecules 33, 7955 (2000).
45T. D. Fornes, P. J. Yoon, D. L. Hunter, H. Keskula, and D. R. Paul, Polymer 43, 5915 (2002).
46R. H. Loeppert, Jr., M. M. Mortland, and T. J. Pinnavaia, Clays and Clay Minerals 27, 201 (1979).
47R. A. Vaia, and E. P. Giannelis, Macromolecules 30, 7990 (1997).
48A. C. Balazs, C. Singh, and E. Zhulina, Macromolecules 31, 8370 (1998).
49A. J. Guenthner, and T. Kyu, J. Polym. Sci., Part B: Polym. Phys. 38, 2366 (2000).
50P. Nawani, M. Y. Gelfer, B. S. Hsiao, A. Frenkel, J. W. Gilman, and S. Khalid, Langmuir 23, 9808 (2007).
51W. J. Blau, and R. B. Padamati, (for Trinity College, Dublin) European Patent WO 2007119231, October 25, 2007.
52B. P. Grady, P. R. Start, and K. A. Mauritz, J. Polym. Sci. Part B: Polym. Phys. 39, 197 (2001).
53Y. Abe, and T. Misono, J. Polym. Sci. Polym. Chem. 21, 41 (1983).
54T. Gunji, Y. Nagao, T. Misono, and Y. Abe, J. Po1m. Sci. Part A: Polym. Chem. 30, 1779 (1992).
55H. Wang, W. Zhong, P. Xu, and Q. Du, Comp. Part A: Appl. Sci. and Manuf. 36, 909 (2005).
56www.prc.gatech.edu, accessed Feb. 7, 2008.
57M. S. Dresselhaus, “Graphite Fibers and Filaments,” Springer-Verlag, London, UK, 1988.
58www.benbest.com/cryonics/lessons.html, accessed May 21, 2007.
59M. S. Dresselhaus, Y. M. Lin, O. Rabin, A. Jorio, A. G.Souza Filho, M. A. Pimenta, R. Saito, G. G. Samsonidze, and
G. Dresselhaus, Mater. Sci. Eng. C23, 129 (2003).
60S. Iijima, Nature 354, 56 (1991).
61http://www.seas.upenn.edu/mse/research/nanotubes.html, access date 08.02.2008.
62J. H. Park, and S. C. Jana, Polymer 44, 2091 (2003).
63A. Thess, R. Lee, P. Nkolaev, H. Dai, P. Pettit, J. Robert, C. Xu, Y. H. Lee, S. G. Kim, A. G. Rinzler, D. T. Colbert, G.
E. Scuseria, D. Tomanek, J. E. Fischer, and R. E. Smalley, Science 273, 483 (1996).
64A. G. Rinzler, J. Liu, H. Dai, P. Nikolaev, C. B. Huffman, and F. J. Rodriguez-Macias, Appl. Phys. A 67, 29 (1998).
458 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

65P. C. Eklund, B. K. Pradhan, U. J. Kim, Q. Xiong, J. E. Fischer, A. D. Friedman, B. C. Holloway, K. Jordan, and M.
W. Smith, Nano Lett. 2, 561 (2002).
66Z. P. Huang, J. W. Xu, Z. F. Ren, J. H. Wang, M. P. Siegel, and P. N. Provensio, Appl. Phys. Lett. 73, 3845 (1998).
67G. G. Tibbetts, J. Cryst. Growth 66, 632 (1984).
68G. G. Tibbetts, "Carbon Fibers, Filaments and Composites," Kluwer Academic, Amsterdam, 1990, p. 73.
69J. Kong, A. M. Cassell, and H. Dai, Chem. Phys. Lett. 292, 567 (1998).
70T. W. Ebbesen, P. M. Ajayan, H. Hiura, and K. Tanigaki, Nature 367, 519 (1994).
71J. Liu, A. G. Rinzler, H. Dai, J. H. Hafner, R. K. Bradley, P. J. Boul, A. Lu, T. Iverson, K. Shelimov, C. B. Huffman, F.
Rodriguez-Macias, Y. S. Shon, T. R. Lee, D. T. Colbert, and R. E. Smalley, Science 280, 1253 (1998).
72E. Mizoguti, F. Nihey, M. Yudasaka, S. Ijima, T. Ichihashi, and K. Nakamura, Chem. Phys. Lett. 321, 297 (2000).
73A. R. Harutyunyan, B. K. Pradhan, J. P. Chang, G. G. Chen, and P. C. Eklund, J. Phys. Chem. B 106, 8671 (2002).
74Z. Shi, Y. Lian, F. Liao, X. Zhou, Z. Gu, Y. Zhang, and S. Ijima, Solid State Commun. 112, 35 (1999).
75Y. Zhang, Z. Shi, Z. Gu, and S. Ijima, Carbon 38, 2055 (2000).
76M. A. Hamon, H. Hu, P. Bhowmik, S. Niyogi, S. Zhao, M. E. Itkis, and R. C. Haddon, Chem. Phys. Lett. 347, 8 (2001)
77J. Chen, M. A. Hamon, H. Hu, Y. Chen, A. M. Rao, P. C. Eklund, and R.C. Haddon, Science 282, 95 (1998).
78M.A. Hamon, J. Chen, H. Hu, Y. Chen, M. E. Itkis, A. M. Rao, P. Eklund, and R. C. Haddon, Adv. Mater. 11, 834 (1999).
79http://www.apsci.com/ppi-pyro3.html, access date : 04.04.2008.
80O. C. Wilson, T. Olorunyolemi, A. Jaworski, L. Borum, D.Young, A. Siriwat, E. Dickens, C. Oriakhi, and M. Lerner,
Applied Clay Science 15, 265 (1999).
81F. Leroux, P. Aranda, J. P. Besse, and E. Ruiz-Hitzky, Europ. J. Inorg. Chem. 2003, 1242 (2003).
82P. B. Messermith, and S. I. Stupp, J. Mater. Res. 7, 2599 (1992).
83C. O. Oriakhi, I. V. Farr, and M. Lerner, J. Mater. Chem. 6, 103 (1996).
84N. T. Whilton, P. J.Vickers, and S. Mann, J. Mater. Chem. 7, 1623 (1997).
85F. Cavani, F. Trifiro, and A.Vaccari, Catalysis Today 11, 173 (1991).
86F. R. Costa, Ph.D. Thesis, Leibniz Institute of Polymer Research, Dresden, Nov. 2007.
87Y. You, H. Zhao, and G. F. Vance, J. Mater. Chem. 12, 907 (2002).
88V. Prevot, C. Forano, and J. P. Besse, Appl. Clay Sci. 18, 3 (2001).
89S. Miyata, Clays Clay Minerals 24, 50 (1980).
90V. Abdelsayed, Y. Ibrahim, M. S. El-Shall, and S. Deevi, Appl. Surf. Sci. 252, 3774 (2006).
91J. H. Golden, H. Deng, F. J. DiSalvo, J. M. Frechet, and P. M. Thompson, Science 268, 1463 (1995).
92D. E. Collins, and E. B. Slamovich, Chem. Mater. 11, 2319 (1999).
93H. Liu, X. Ge, Y. Zhu, X. Xu, Z. Zhang, and M. Zhang, Mater. Lett. 46, 205 (2000).
94H. Srikanth, R. Hajndl, C. Chirinos, J. Sanders, A. Sampath, and T.S. Sudarshan, Appl. Phys. Lett. 79, 3503 (2001).
95H. Du, G. Q. Xu, W. S. Chin, L. Huang, and W. Ji, Chem. Mater. 14, 4473 (2002).
96N. A. D. Burke, H. D. Stoever, and F. P. Dawson, Chem. Mater. 14, 4752 (2002).
97J. L. Wilson, P. Poddar, N. A. Frey, H. Srikanth, K. Mohomed, J.P. Harmon, S. Kotha, and J.Wachsmuth, J. Appl. Phys.
95, 1439 (2004).
98B. Govindaraj, N. V. Sastry, and A. Venkataraman, J. Appl. Polym. Sci. 93, 778 (2004).
99R. R. Rakhimov, E. M. Jackson, J. S. Hwang, A. I. Prokofev, I. A. Alexandrov, and A. Y. Karmilov, J. Appl. Phys. 95,
7133 (2004).
100S. Sahoo, and A. K. Bhowmick, J. Appl. Polym. Sci. 106, 3077 (2007).
101J. Wang, and L. Gao, Inorg. Chem. Commun. 6, 877 (2003).
102S. Sahoo, and A. K. Bhowmick, J. Appl. Polym. Sci. 2007 (in press).
103S. Liufu, H. Xiao, and Y. P. Li, Polym. Degrad. Stab. 87, 103 (2005).
104H. A. Ali, and A. A. Iliadis, Thin Solid Films 471, 154 (2005).
 ELASTOMER NANOCOMPOSITES 459

105J. Zheng, R. Ozisik , and R. W.Siegel, Polymer 46, 10873 (2005).

106Y. Xie, J. Huang, B. Li, B. Liu, and Y. T. Qian, Adv. Mater. 12, 1523 (2000).
107Y. D.Li, M. Sui, Y. Ding, G. Zhang, J. Zhuang, and C. Wang, Adv. Mater. 12, 818 (2000).
108J. C. Yu, A. W. Xu, L. Z. Zhang, R. Q. Song, and L.Wu, J. Phys. Chem. B 108, 64 (2004).
109C. Henrist, J. P. Mathieu, C. Vogels, A. Rulmont, and R. Cloots, J. Cryst. Growth 249, 321 (2003).
110J. Lv, L. Qiu, and B. Qu, Nanotechnology 15, 1576 (2004).
111M. Mckelvy, R. Sharma, A. G. Chizmeshya, R. W. Carpenter, and K.Streib, Chem. Mater. 13, 921 (2002).
112C. M. Lieber, A. M. Morales, P. E. Sheehan, E. W. Wong, and P. Yang, "One-Dimensional Nanostructures: Rational
Synthesis, Novel Properties And Applications," in “Chemistry on the Nanometer Scale,” Proceedings of the Robert A.
Welch Foundation Conferences on Chemical Research: Chemistry on the Nanometer Scale ,Houston, TX, 1996, Vol.
40, p. 165-187.
113R. C. Xie and B. J. Qu., Chinese Patent Application 00135436, 2001.
114M. Alexandre, G. Beyer, C. Henrist, R. Cloots, A. Rulmont, R. J’erome, and P. Dubois, Macromol. Rapid Commun.
22, 643 (2001).
115C. H. Chen, C. C. Teng, S. F. Su, W. C. Wu, and CH. Yang, J. Polym. Sci. Part B: Polym. Phys. 44, 451 (2006).
116C. M. Deng, M. Chen, N. J. Ao, D. Yan, and Z. Q. Zheng, J. Appl. Polym. Sci. 101, 3442 (2006).
117X. Su, Y. Hua, J. Qiao, Y. Liu, X. Zhang, J. Gao, Z. Song, F. Huang, and M. Zhang, Macromol. Mater. Eng. 289, 275
(2004).
118S. Mishra, S. H. Sonawane, N. Badgujar, K. Gurav, and D. Patil, J. Appl. Polym. Sci. 96, 6 (2005).
119F. L. Jin, and S. J. Park, Mater. Sci. Eng. A A478, 406 (2008).
120L. Jiang, Y. C. Lam, K. C. Tam, T. H. Chua, G. W. Sim, and L. S. Ang, Polymer 46, 243 (2005).
121http://www.nanomt.com/specialty/index.asp, access date: 07.02.2008.
122http://www.solvaypcc.com/safety_environment/0,0,1000028-_EN,00.html, access date: 07.02.2008.
123L.A.Utracki, "Clay-Containing Polymeric Nanocomposites," Vol. 1 & 2. Rapra Technology Limited, Shawbury, 2004.
124A. Clearfield, W. L. Duax, A. S. Medina, G. D. Smith, and J. R. Thomas, J. Phys. Chem. 73, 3424 (1969).
125U. Costantino, N. Nocchetti, F.Marmottini, and R. Vivani, Eur. J. Inorg. Chem. 10, 1447 (1998).
126C. Ozdilek, K. Kazimierczak, D.van der Beek, and S. J. Piken, Polymer 45, 5207 (2004).
127R. P. Tandon, D. R.Choubey, R. Singh, and N. C. Soni, J. Mat. Sci. Lett. 12, 1182 (1993).
128G. Y.Yurkov, D. A. Astafíev, L. N. Nikitin, Yu. A. Koksharov, N. A. Kataeva, E. V. Shtykova, K. A. Dembo, V. V.
Volkov, A. R. Khokhlov, and S. P. Gubin, Inorg. Mat. 42, 496 (2006).
129K. G. Nair, and A. Durfresne, Biomacromol. 4, 666 (2003).
130M. Bhattacharya, M. Maiti, and A. K. Bhowmick, paper #A-16, p.175, in proceedings of International Conference on
Rubber and Rubber-Like Materials, Kharagpur, India, January 2008.
131H. Acharya, S. K. Srivastava, and Anil K. Bhowmick, Comp. Sci. Tech. 67, 2807 (2007).
132www.nanoclay.com, access date: 07.02.2008.
133http://chemistry.anl.gov/Catalyst%20Design/Giselle.htm as on 24 Aug. 2006.
134F. Dellisanti, and G. Valdre, Appl. Clay Sci. 28, 233 (2005).
135T. J. Pinnavaia, R. H. Raythatha, (for Michigan State University), US 4629712, Dec., 1986.
136M.Bhattacharya, M. Maiti, and A. K. Bhowmick, accepted for publication in RUBBER CHEM. TECHNOL. (2008).
137J. J. George, R.Sengupta, and A. K. Bhowmick, J. Nanosci. Nanotech. 8, 1913, (2007).
138J. Madejova, Vibrational Spectroscopy 31, 1 (2003).
139M. Okamoto, Rapra Review Report 163, 14, (2003).
140K. A. Carrado, and A. Awaluddin, 206th National Meeting, American Chemical Society, Chicago, IL, August 22-27,
1993.
141M. Maiti, and A. K. Bhowmick, J. Appl. Polym. Sci. in press (2008).
460 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

142L. Zhang, K. C. Tam, L. H. Gan, C. Y. Yue, Y. C. Lam, and X. Hu, J. Appl. Polym. Sci. 87, 1484 (2003).
143www.advancedmaterials.us, access date 14.02.2008.
144http://www.solvaypcc.com, access date 14.02.2008.
145E. Bergaya, J. Porous Materials 2, 91 (1995).
146A. Peigney, Ch. Laurent, E. Flahaut, R.R. Bacsa, and A. Rousset, Carbon 39, 507 (2001).
147L. S. Somlai, S. A. Bandi, D. A. Schiraldi, and L. J. Mathias, AIChE Journal, 52, 1162 (2005).
148IMartin-Gullona, J. Veraa, J. A. Conesaa, J. L. Gonz·lezb, and C. Merinob, Carbon 44, 1572 (2006).
149J. J. George, and A. K.Bhowmick, J. Mater. Sci. 43, 702 (2008).
150G. Kraus, Ed., "Reinforcement of Elastomers," Interscience, New York, 1965.
151C. M. Blow, "Rubber Technology and Manufacture," Butterworth, London, 1971.
152A. K. Bhowmick, M. M. Hall, and H. Benary, Eds., "Rubber Products Manufacturing Technology," Marcel Dekker
Inc., USA, 1994
153H. Ishida, "Interfacial Phenomena in Polymer, Ceramic and Metal Matrix Composites," Elsevier, New York, 1988.
154A.I. Medalia, and G. Kraus, in "Science and Technology of Rubber," 2nd ed., J. E. Mark, B. Erman, and F. R. Eirich,
Eds., Academic Press, San Diego, 1994.
155S. Wolff, and M-J.Wang, RUBBER CHEM. TECHNOL.65, 329 (1992).
156S. Wolff, RUBBER CHEM. TECHNOL. 69, 325 (1996).
157G. R. Hamed, RUBBER CHEM. TECHNOL. 73, 524 (2000).
158S. Kohjiya, and Y.Ikeda, RUBBER CHEM. TECHNOL. 73, 534 (2000).
159M. Pramanik, S.K. Srivastava, B.K. Samantaray, and A. K. Bhowmick, J. Appl. Polym. Sci. 87, 2216 (2003).
160M. Ganter, W. Gronski, P. Reichert, and R. Mulhaupt, RUBBER CHEM. TECHNOL. 74, 221 (2001).
161M. Ganter, W. Gronski, H. Semke, T. Zilg, C. Thomann, and R. Mulhaupt, Kautsch. Gummi Kunstst. 54, 166 (2001).
162S. Sadhu, and A. K. Bhowmick, J. Appl. Polym. Sci. 92, 698 (2004)
163S. Joly, G. Garnaud, R. Ollitrault, and L. Bokobza, Chem. Mater. 14, 4202 (2002).
164R. Magaraphan, W. Thaijaroen, and R. Lim-Ochakun, RUBBER CHEM. TECHNOL. 76, 406 (2003).
165M. A. Lopez-Manchado, B. Herrero, and M. Arroyo, Polym. Int. 53, 1766 (2004).
166Y. Kazumasa, H. Haruumi, O. Tetsuro, and K. Hokoku, Fukuoka-ken Kogyo GijutsuSenta 15, 35 (2005).
167A. Bandyopadhyay, M. De Sarkar, and A. K. Bhowmick, RUBBER CHEM. TECHNOL. 77, 830 (2004).
168Y. T. Vu, J. E. Mark, L. H. Pham, and M. Engelhardt, J. Appl. Polym. Sci. 82, 1391 (2001).
169S. Sadhu and A. K. Bhowmick, J. Polym. Sci. Part B: Polym. Phys. 42, 1573 (2004).
170Y. Liang, Y. Wang, Y. Wu, Y. Lu, H. Zhang, and L. Zhang, Polymer Testing 24, 12 (2005).
171M. Maiti, S. Sadhu, and A. K. Bhowmick, J. Polym. Sci. Part B: Polym. Phys. 42, 4489 (2004).
172M. Maiti, and A. K. Bhowmick, J. Polym. Sci. Part B: Polym. Phys. 44, 162 (2006).
173Y. Kojima, K. Fukumori, A. Usuki, A. Okada, and T. Kurauchi, J. Mater. Sci. Lett. 12, 889 (1993).
174S. K. Lim, J. W. Kim, I. J. Chin, and H. J. Choi, J. Appl.Polym. Sci. 86, 3735 (2002).
175S. Sahoo , S. Kar, A. Ganguly, M. Maiti, and A. K. Bhowmick, Polym. Polym. Comp. 16, 193 (2008).
176M. Sennett, E. Welsh, J. B. Wright, W. Z. Li, J. G. Wen, and Z. F. Ren, Appl. Phys. A. 76, 111 (2003).
177M. J. Biercuk, M. C. Llaguno, M. Radosavljevic, J. K. Hyun, A. T. Johnson, and J. E. Fischer, Appl. Phys. Lett. 80,
2767 (2002).
178I. C. Finegan, and G. G. Tibbetts, J. Mater. Res. 16, 1668 (2001).
179Y. A. Kim, T. Hayashi, Y. Fukai, M. Endo, T. Yanagisawa, and M. S. Dresselhaus, Chem. Phys. Lett. 355, 279 (2002).
180Y. K. Kim, A. F. Lewis, P. K. Patra, S. B. Warner, and P. Calvert, National Textile Center Research Briefs-Materials
Competency, p. 24, June, 2001.
181M. Zhang, M. Yudasaka, A. Koshio, C. Jabs, T. Ichihashi, and S. Iijima, Appl. Phys. A. 74, 7 (2002).
182A. S. Lobach, N. G. Spitsina, S. V. Terehov, and E. D. Obraztsova, Phys. Solid State 44, 475 (2002).
 ELASTOMER NANOCOMPOSITES 461

183M. Rao, R. Andrews, and F. Derbyshire, Energeia 9, 1 (1998).

184J. M. Moon, K. H. An, Y. H. Lee, Y. S. Park, D. J. Bae, and G. S. Park, J. Phys. Chem. B. 105, 5677 (2001).
185S. Bandow, S. Asaka, X. Zhao, and Y. Ando, Appl. Phys. A. 67, 23 (1998).
186G. S. Duesberg, J. Muster, H. J. Byrne, S. Roth, and M. Burghard, Appl. Phys. A. 69, 305 (1999).
187M. Yudasaka, M. Zhang, C. Jabs, and S. Iijima, Appl. Phys. A. 71, 449 (2000).
188H. Ago, T. Kugler, F. Cacialli, W. R. Salaneck, M. S. P. Shaffer, A. H. Windle, and R. H. Friend, J. Phys. Chem. B.
103, 8116 (1999).
189A. Star, J. F. Stoddart, D. Steuerman, M. Diehl, A. Boukai, E. W. Wong, X. Yang, S. W. Chung, H. Choi, and J. R.
Heath, Angew. Chem. Int. Ed. 40, 1721 (2001).
190X. Gong, J. Liu, S. Baskaran, R. D. Voise, and J. S. Young, Chem. Mater. 12, 1049 (2000).
191M. Bratcher, B. Gerstein, H. Ji, and J. Mays, Making Functional Materials with Nanotubes Symposium (Materials
Research Society Symposium Proceedings, Vol. 706, p. 323), Watersdale, Pa. 2002.
192D. H. Yu, Y. Z. Yue, J. de C. Christiansen, S. Kazoui, and N. Minami, Proceedings of the Nordic Meeting on Materials
and Mechanics, pp. 147, Denmark, 2000.
193J. L. Bahr, and J. M. Tour, Chem. Mater. 13, 3823 (2001).
194V. Georgakilas, K. Kordatos, M. Prato, D. M. Guldi, M. Holzinger, and A. Hirsch, J. Am. Chem. Soc. 124, 760 (2002).
195J. P. Harmon, P. A. O. Muisener, L. Clayton, J. DíAngelo, A. K. Sikder, A. Kumar, M. Meyyaooan, and A. M. Cassell,
Surface Engineering-Fundamentals and Applications (Mater. Res. Society Symposium Proceedings, Vol. 697, pp.
425), Boston, 2001.
196H. Bubert, S. Haiber, W. Brandl, G. Marginean, M. Heintze, and V. Bruse, Diamond Related Materials 12, 811 (2003).
197J. C. Kearns, and R. L. Shambaugh, J. Appl. Polym. Sci. 86, 2079 (2002).
198K. T. Lau, and D. Hui, Comp. Pt B Eng. 33, 263 (2002).
199D. Qian, G. J. Wagner, W. K. Liu, M. F. Yu, and R. S. Ruoff, Appl. Mech. Rev. 55, 495 (2002).
200K. Kueseng, and K. I. Jacob, Europ. Polym. J. 42, 220 (2005).
201F. R. Ahmadun, S. A. Rashid, and M. A. Atieh, Fullerenes, Nanotubes, Carbon Nanostructures 15, 207 (2007).
202M. A. Atieh, N. Girun, E. S. Mahdi, and H. Tahir, C. T. Guan, M. F. Alkhatib, F. R. Ahmadun, and D. R. Baik,
Fullerenes, Nanotubes, Carbon Nanostructures 14, 641 (2006).
203N.Girun, F. R. Ahmadun, S. A. Rashid, and M. A. Atieh, Fullerenes, Nanotubes, Carbon Nanostructures 15, 207
(2007).
204M. J. Jiang, Z. M. Dang, and H. P. Xu, Appl. Physi. Lett. 90, 042914/1 (2007).
205L.Ye, P. Ding, M. Zhang, and B. Qu, J. Appl. Polym. Sci. 107, 3694 (2008).
206M. D. Frogley, D. Ravich, and H. D. Wagner, Compos. Sci. Technol. 63, 1647 (2003).
207A. Isayev, (for University of Akron) European Patent, WO 2007145918 A3, Dec. 21, 2007.
208L. Yang, Y. Hu, H. Guo, L. Song, Z. Chen, and W. Fan, J. Appl. Polym. Sci. 102, 2560 (2006).
209L. Chen, L. Lu, D.Wu, and G.Chen, Polym. Comp. 28, 493 (2007).
210D. W. Kang, H. G. Yeo, and K. S. Lee, J. Inorg. Organometallic Polym. 14, 73 (2004).
211S. Varghese, and J. Karger-Kocsis, Polymer 44, 4921 (2003).
212J. Ma, P.Xiang, Y. W. Mai, and L. Q. Zhang, Macromol. Rapid Comm. 25, 1692 (2004).
213Q. X. Jia, Y. P.Wu, Y. Q.Wang, M. Lu, J. Yang, and L. Q.Zhang, J. Appl. Polym. Sci. 103, 1826 (2007).
214M. Abdollahi, A. Rahmatpour, J. Aalaie, and H. H. Khanli, e-Polymers No. 074 (2007).
215L. Zhang, Y. Wang, Y. Wang, Y. Sui, and D. Yu, J. Appl. Polym. Sci. 78, 1873 (2000).
216Y. Wang, H. Zhang, Y. Wu, J. Yang, and L. Zhang, J. Appl. Polym. Sci. 96, 318 (2005).
217R. Stephen, R. Alex, T. Cherian, S. Varghese, K. Joseph, and S. Thomas, J. Appl. Polym. Sci. 101, 2355 (2006).
218Y. P. Wu, L. Q. Zhang, Y. Q. Wang, Y. Liang, and D. S. Yu, J. Appl. Polym. Sci. 82, 2842 (2001).
219Y. P. Wu, Q. X. Jia, D. S. Yu, and L. Q. Zhang, J. Appl. Polym. Sci. 89, 3855 (2003).
462 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

220S. Varghese, K. G. Gatos, A. A. Apostolov, and J. Karger-Kocsis, J. Appl. Polym. Sci. 92, 543 (2004).
221M. Ajbani, J. F. Geiser, and D. K. Parker, (for The Goodyear Tire & Rubber Co.), U.S. Patent Appl., US 2003144401
A1,July 31, 2003.
222X. Yang, M. P. Cohen, M. L. Senyek, D. K. Parker, S. W. Cronin, L. T. Lukich, W. P. Francik, and C. Gurer, (for The
Goodyear Tire & Rubber Co.), U.S. Patent Appl., US 2005065266 A1, March 24 , 2005.
223J. D. Wang, Y. F. Zhu, X. W. Zhou, G. Sui, and J. Liang, J. Appl. Polym. Sci. 100, 4697 (2006).
224C. Gauthier, L. Chazeau, T. Prasse, and J. Y. Cavaille, Compos. Sci. Technol. 65, 335 (2006).
225S. Manroshan, and A. Baharin, J. Appl. Polym. Sci. 96, 1550 (2005).
226K. G. Nair, and A. Dufresne, Biomacromol. 4, 657 (2003).
227A. F. Martins, L. L. Y. Visconte, R. H. Schuster, F. Boller, and R. C. R. Nunes, Kautsch. Gummi Kunstst. 57, 446
(2004).
228A. F. Martins, L. L. Y. Visconte, and R. C. R. Nunes, "Natural Polymers and Composites IV," Proceedings from the
International Symposium on Natural Polymers and Composites, 4th, Sao Pedro, Brazil, 596, 2002.
229Y. P. Wu, Y. Ma, Y. Q. Wang, and L. Q. Zhang, Macromol. Mater. Eng. 289, 890 (2004).
230A. Usuki, A. Tukigase, and M. Kato, Polymer 43, 2185 (2002).
231K. G. Gatos, R. Thomann, and J. Karger-Kocsis, Polym. Int. 53, 1191 (2004).
232K. G. Gatos, and J. Karger-Kocsis, Polymer 46, 3069 (2005).
233Y. Ma, Y.-P. Wu, and Y.-Q.Wang, and L. Q. Zhang, J. Appl. Polym. Sci. 99, 914 (2006).
234S. Varghese, J. Karger-Kocsis, and K. G. Gatos, Polymer 44, 3977 (2003).
235M. Arroyo, M.A. Lopez-Manchado, and B. Herrero, Polymer 44, 2447 (2003).
236M. A. Lopez-Manchado, M. Arroyo, B. Herrero, and J. Biagiotti, J. Appl. Polym. Sci. 89, 1 (2003).
237P. L. Teh, Z. A. Mohd Isak, A. S. Hashim, J. Karger-Kocsis, and U. S. Ishiaku, J. Appl. Polym. Sci. 94, 2438 (2004).
238S. Varghese and J. Karger-Kocsis, J. Appl. Polym. Sci. 91, 813 (2004).
239P. L. Teh, Z. A. Mohd Isak, A. S. Hashim, J. Karger-Kocsis, and U.S. Ishiaku, J. Appl. Polym. Sci. 100, 1083 (2006).
240F. Schon, and W. Gronski, Kauts. Gummi Kunst. 56, 166 (2003).
241J. T. Kim, D. Y. Lee, T. S. Oh, and D. H. Lee, J. Appl. Polym. Sci. 89, 2633 (2003).
242J. T. Kim, T. S. Oh, and D. H. Lee, Polym. Int. 52, 1058 (2003).
243J. T. Kim, T. S. Oh, and D. H. Lee, Polym. Int. 52, 1203 (2003).
244C. Nah, H. J. Ryu, W. D. Kim, and Y. W. Chang, Polym. Int. 52, 1359 (2003).
245H. Acharya, M. Pramanik, S. K. Srivastava, and A. K.Bhowmick, J. Appl. Polym. Sci. 93, 2429 (2004).
246Y. W. Chang, Y. Yang, S. Ryu, and C. Nah, Polym. Int. 51, 319 (2002).
247H. Zheng, Y. Zhang, Z. Peng, and Y. Zhang, J. Appl. Polym. Sci. 92, 638 (2004).
248A. Fakhruíl-Razi, M. A. Atieh, N. Girun, T. G. Chuah, M. El-Sadig, and D. R. A. Biak, Comp. Struct. 75, 496 (2006).
249D. W. Liu, X. S. Du, and Y. Z. Meng, Polym, Polym. Compos. 13, 815 (2005).
250T. Noguchi, and A. Magario, (for Nissin Kogyo Co., Ltd,) European Pat. Appl., EP 2006-253466, June 30, 2006.
251J. Gu, D. Jia, Y. Luo, R. Cheng, Hecheng Xiangjiao Gongye 28, 374 (2005).
252S. Mishra, and N. G. Shimpi, J. Sci. Ind. Res. 64, 744 (2005).
253S. Mishra, N. G. Shimpi, and U. D. Patil, J. Polym. Res. 14, 449 (2007).
254G. Lin, M. Tian, Y. L. Lu, and X. J. Zhang, and L. Q. Zhang, Polymer J. (Japan) 38, 498 (2006).
255Y. Chen, (for Shanghai University of Engineering Technology), Chinese Patent, CN1386788, Dec. 25, 2002.
256S. Mishra, and N. G. Shimpi, J. Appl. Polym. Sci. 104, 2018 (2007).
257W. S. Jin, H. S. Lee, and C. Nah, Polymer (Korea) 28, 185 (2004).
258S. Patel, A. Bandyopadhyay, V. Vijaybaskar, and A. K. Bhowmick, RUBBER CHEM. TECHNOL. 79, 820 (2006).
259H. Datta, N. K. Singha, and A. K. Bhowmick, Macromolecules 41, 50 (2008).
260J. Xu, W. Pang, and W. Shi, Thin Solid Films 514, 69 (2006).
 ELASTOMER NANOCOMPOSITES 463

261D. Blanc, W. Zhang, C. Massard, and J. Mugnier, Optical Mater. 28, 331 (2006).
262Z. Roslaniec, G. Broza, and K. Schulte, Composite Interfaces 10, 95 (2003).
263C. I. Park, O. O. Park, J. G. Lim, and H. J. Kim, Polymer 42, 7465 (2001).
264A. B. Morgan, and J. W. Gilman, J. App. Polym. Sci. 87, 1329 (2003).
265V. Causin, C. Marega, A. Mariog, and G. Ferrara, Polymer 46, 9533 (2005).
266R. Roe, "Methods of X-Ray and Neutron Scattering in Polymer Science," Oxford University Press, New York, 2000,
p. 199.
267L. Alexander, "X-Ray Diffraction Methods in Polymer Science," Wiley, New York, 1970.
268A. Bafnaa, G. Beaucagea, F. Mirabellab, and S. Mehta, Polymer 44, 1103 (2003).
269D. L. Ho, and C. Glinka, J. Chem. Mater. 15, 1309 (2003).
270H. J. M. Hanley, C. D. Muzny, D. L. Ho, and C. J. Glinka, Langmuir 19, 5575 (2003).
271D. F. Eckel, M. P. Balogh, P. D. Fasulo, and W. R. Rodgers, J. App. Polym. Sci. 93, 1110 (2004).
272M. Maiti, and A. K. Bhowmick, Polymer 47, 6156 (2006).
273A. Ganguly, M. De Sarkar, and A. K. Bhowmick, J. Polym. Sci., Part B: Polym. Phys. 45, 52 (2006).
274Z. L. Wang, Adv. Mater. 15, 1497 (2003).
275L. J. Mathias, R. D. Davis, and W. L. Jarrett, Macromolecules 32, 7958 (1999).
276D. L.VanderHart, A. Asano, and J. W. Gilman, Macromolecules 34, 3819 (2001).
277D. L.VanderHart, A. Asano, and J. W. Gilman, Chem. Mater. 13, 3796 (2001).
278S. K. Sahoo, D. W. Kim, J. Kumar, A. Blumstein, and A. L. Cholli, Macromolecules 36, 2777 (2003).
279Y. Bensimon, B. Deroide, and J. V. Zanchetta, J. Phys. Chem. Solid 60, 813 (1999).
280G. Jeschke, G. Panek, S. Schleidt, and U. Jonas, Polym. Eng. Sci. 44, 1112 (2004).
281L. S. Loo, and K. K. Gleason, Macromolecules 36, 2587 (2003).
282R. D. Davis, A. J. Bur, M. McBrearty, Y H. Lee, J. W. Gilman, and P. R. Start, Polymer 45, 6487 (2004).
283A. J. Bur, Y S. Lee, S. C. Roth, and P. R. Start, Polymer 46, 10908 (2005).
284A. Bafna, G. Beaucage, F. Mirabella, G. Skillas, and S. Sukumaran, J. Polym. Sci. Part B: Polym. Phys. 39, 2923
(2001).
285M. Maiti, and A. K. Bhowmick, Polym. Eng. Sci. 47, 1777 (2007).
286M. Galimberti, A. Lostritto, A. Spatola, and G. Guerra, Chem. Mater. 19, 2495 (2007).
287A. Ganguly, Y. Li, and A. K. Bhowmick, Macromolecules 10•1021/ma800274y (2008).
288L. J. Mathias, R. D. Davis, and W. L. Jarrett, Macromolecules 32, 7958 (1999).
289S. N. Magonov, V. Ellings , and M. H. Whangbo, Surface Sci. 375, L385 (1997).
290G. G. Tibbetts, G. L. Doll, D. W. Gorkiewicz, J. J. Moleski, M. A. Perry, C. J. Dasch, and M. J. Balogh, Carbon 31,
1039 (1993).
291M. S. Dresselhaus, G. Dresselhaus, K. Sugihara, I. L. Spain, and H. A. Goldberg, "Graphite Fibers and Filaments,"
Berlin, Springer-Verlag, 1988.
292S. Netrabukkana, and C. Pattamaprom, Chiang Mai J. Science 32, 391(2005).
293R. Stephen, C. Ranganathaiah, S. Varghese, K. Joseph, and S. Thomas, Polymer 47, 858 (2006).
294Q. Jia, Y. Wu, X. Ping, Y. Xin, Y. Wang, and L. Zhang, Polym., Polym. Compst. 13, 709 (2005).
295Y. Wu, Y. Wang, H. Zhang, Y. Wang, D. Yu, L. Zhang, and J. Yang, Compos. Sci. Technol. 65, 1195 (2005).
296J. Sharif, W. Zin, M. Wan, D. Mohd, Z. H. Khairul, and M. H. Ahmad, Polym. Testing 24, 211 (2005).
297P. L. Teh, Z. A. Mohd Ishak, A. S. Hashim, J. Karger-Kocsis, and U. S. Ishiaku, Euro. Polym. J. 40, 2513 (2004).
298A. Jacob, P. Kurian, and A. S. Aprem, Int. J. Polymer. Mater. 56, 593 (2007).
299W. Zukas, M. Sennett, E. Welsh, A. Rodriguez, D. Ziegler, and P. Touchet, Transformational Science and Technology
for the Current and Future Force: Proceedings of the 24th Us Army Science Conference 42, 467 (2006).
300W. Kim, S. K. Kim, J. H. Kang, Y. Choe, and Y. W. Chang, Macromol. Res. 14, 187 (2006).
464 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

301L. F. Valadares, C. A. P. Leite, and F. Galembeck, Polymer 47, 672 (2006).

302A.S. Aprem, A. Jacob, and S.N. Pal, "Natural Rubber Latex-Layered Silicate Nanocomposites With Excellent
Permeation Resistance And Mechanical Properties" in Latex 2006, International Conference on Latex and Latex Based
Products, 4th, Frankfurt, Germany, Jan.24-26, 2006, paper 21.
303S. Varghese (for Rubber Research Institute of India), Indian Patent Appl. IN2005CH00562 A, July 27, 2007.
304H. Sarashi (for Sumitomo Rubber Industries Co., Ltd.), Japanese Patent JP2005113015 A, April 28, 2005.
305R. Stephen, S. Thomas, K. V. S. N. Raju, S. Varghese, K. Joseph, and Z. Oommen, RUBBER CHEM. TECHNOL. 80, 672
(2007).
306S. D. Li, Z. Peng, L. X. Kong, and J. P. Zhong, J. Nanosc. Nanotech. 6, 541 (2006).
307A. Ansarifar, S. F. Shiah, N. Ibrahim, and A. Azhar, "Rubberchem 2004," 4th International Rubber Chemicals,
Compounding and Mixing Conference, Birmingham, United Kingdom, Nov., 2004 .
308C. Nah, D. H. Kim, W. D. Kim, W. B. Kwacheon, and S. Kaang, Kautsch. Gummi Kunstst. 57, 224 (2004).
309Y. Ikeda, Kautsch. Gummi Kunstst. 58, 455 (2005).
310M. Knite, V. Teteris, and A. Kiploka, Mater. Sci. Eng., C: Biomimetic Supramolecular Systems C23, 787 (2003).
311M. Knite, V. Teteris, B. Polyakov, and D. Erts, Mater. Sci. Eng., C: Biomimetic Supramolecular Systems C19, 15
(2002).
312S. Sahoo, M. Maiti, A. Ganguly, J. J. George, and A. K. Bhowmick, J. Appl. Polym. Sci. 105, 2407 (2007).
313C. Pina-Hernandez, L. Hernandez, L. M. Flores-Velez, L. F. del Castillo, and O. Dominiguez, J. Mater. Eng. Perform.
16, 470 (2007).
314H. Angellier, S. Molina-Boisseau, and A. Dufresne, Macromolecules 38, 9161 (2005).
315K. G. Nair, and A. Dufresne, Biomacromolecules 4, 666 (2003).
316D. E. El-Nashar, S. H. Mansour, and E. Girgis, J. Mater. Sci. 41, 5359 (2006).
317A. Bandyopadhyay, M. De Sarkar, and A. K. Bhowmick, J. Polym. Sci., Part B: Polym. Phys. 43, 2399 (2005).
318A. Bandyopadhyay, M. De Sarkar, and A. K. Bhowmick, J. Appl. Polym. Sci. 95, 1418 (2005).
319A. Bandyopadhyay, M. De Sarkar, and A. K. Bhowmick, J. Mater. Sci. 41, 5981 (2006).
320A. Bandyopadhyay, M. De Sarkar, and A. K. Bhowmick, RUBBER CHEM. TECHNOL. 78, 806 (2005).
321A. Bandyopadhyay, and A. K. Bhowmick, Plast. Rubber Compst. 35, 210 (2006).
322A. Bandyopadhyay, V. Thakur, S. Pradhan, and A. K. Bhowmick, Communicated to J. Appl. Polym. Sci. (2008).
323S. Wang, Y. Zhang, W. Ren, Y. Zhang, and H. Lin, Polym. Testng. 24, 766 (2005).
324S. Wang, Z. Peng, Y. Zhang, and Y. Zhang, Polym. Polym.Compst. 13, 371 (2005).
325S. Wang, Y. Zhang, Z. Peng, and Y. Zhang, J. Appl. Polym. Sci. 99, 905 (2006).
326S. Sadhu, and A. K. Bhowmick, J. Polym. Sci., Part B: Polym. Phys. 43, 1854 (2005).
327M. Song, C. W. Wong, J. Jin, A. Ansarifar, Z. Y. Zhang, and M. Richardson, Polym. Int. 54, 560 (2005).
328M. S. Kim, G. H. Kim, and S. R. Chowdhury, Polym. Eng. Sci. 47, 308 (2007).
329X. Wang, Y. Gao, K. Mao, G. Xue, T. Chen, J. Zhu, B. Li, P. Sun, Q. Jin, D. Ding, and A. C. Shi, Macromolecules 39,
6653 (2006).
330M. Liao, W. Shan, J. Zhu, Y. Li, and H. Xu, J. Polym. Sci., Part B: Polym. Phys. 43, 1344 (2005).
331S. Mishra, and N. G. Shimpi, Polym.-Plast. Technol. Eng. 47, 72 (2008).
332S. Sadhu, and A. K. Bhowmick, RUBBER CHEM. TECHNOL. 78, 321 (2005).
333S. Sadhu, and A. K. Bhowmick, J. Mater. Sci. 40, 1633 (2005).
334H. Zhang, Y. Wang, Y. Wu, L. Zhang, and J. Yang, J. Appl. Polym. Sci. 97, 844 (2005).
335Y. Liang, Y. Lu, Y. Wu, Y. Ma, and L. Zhang, Macromol. Rapid Commun. 26, 926 (2005).
336Z. F. Wang, B. Wang, N. Qi, H. F. Zhang, and L. Q. Zhang, Polymer 46, 719 (2005).
337Y. Wu, Q. Jia, D. Yu, and L. Zhang, Polym. Testng. 23, 903 (2004).
338L. Zhang, Y. Wang, Y. Wang, S. Yuan, and D. Yu, J. Appl. Polym. Sci. 78, 1873 (2000).
 ELASTOMER NANOCOMPOSITES 465

339Q. X. Jia, Y. P. Wu, Y. L. Xu, H. H. Mao, and L. Q. Zhang, Macromol. Mater. Eng. 291, 218 (2006).
340W. Kim, B. S. Kang, S. G. Cho, C. S. Ha, and J. W. Bae, Compos. Interfaces 14, 409 (2007).
341A. Mousa, and J. Karger-Kocsis, Macromol. Mater. Eng. 286, 260 (2001).
342Z. Zhang, L. Zhang, Y. Li, and H. Xu, Polymer 46, 129 (2005).
343X. Zhou, Y. Zhu, Q. Gong, and J. Liang, Mater. Lett. 60, 3769 (2006).
344M. A. Kader, K. Kim, Y. S. Lee, and C. Nah, J. Mater. Sci. 41, 7341 (2006).
345D. Choi, M. A. Kader, B. Cho, Y. Huh, and C. Nah, J. Appl. Polym. Sci. 98, 1688 (2005).
346Y. Kim, and J. L.White, J. Appl. Polym. Sci. 96, 1888 (2005).
347J. Kim, T. Oh, and D. Lee, Polym. Int. 53, 406 (2004).
348C. Nah, J. Ryu Hyune, S. Han, J. Rhee, and M. Lee, Polym. Int. 50, 1265 (2001).
349W. G.Hwang, K. H. Wei, and C. M. Wu, Polymer 45, 5729 (2004).
350W. G. Hwang, and K. H. Wei, Polym. Eng. Sci. 44, 2117 (2004).
351M. Han, S. A. Park, and E. Kim, Polym. Preprints 46, 509 (2005).
352X. Colom, F. Carrillo, F. Andreu-Mateu, J. Canavate, and J. J. Sunol, Recent Res. Dev. Appl. Polym. Sci. 3, 243 (2006).
353R. N. Mahaling, G. K. Jana, C. K. Das, H. Jeong, and C. S. Ha, Macromol. Res. 13, 306 (2005).
354V. L. C. Lapa, J. C. M. Suarez, L. L. Y. Visconte, and R. C. R. Nunes, J. Mater. Sci. 42, 9934 (2007).
355A. Choudhury, A. K. Bhowmick and C. Ong, Communicated to Polymer (2008).
356K. G. Gatos, L. Szazdi, B. Pukanszky, and J. Karger-Kocsis, Macromol. Rapid Commun. 26, 915 (2005).
357K. G. Gatos, N. S. Sawanis, A. A. Apostolov, R. Thomann, and J. Karger-Kocsis, Macromol. Mater. Eng. 289, 1079
(2004).
358W. Herrmann, C. Uhl, G. Heinrich, and D. Jehnichen, Polym. Bulletin 57, 395 (2006).
359D. Yue, Y. Liu, Z. Shen, and L. Zhang, J. Mater. Sci. 41, 2541 (2006).
360H. Acharya, and S. K. Srivastava, Macromol. Res. 14, 132 (2006).
361B. Haidar, C. Vaulot, C. Da Silva, and A. Vidal, PMSE Preprints 93, 862 (2005).
362S. Morlat-Therias, B. Mailhot, J. Gardette, C. Da Silva, B. Haidar, and A.Vidal, Polym. Degrad. Stab. 90, 78 (2005).
363S. J. Ahmadi, Y. Huang, and W. Li, J. Compst. Mater. 39, 745 (2005).
364S. J.Ahmadi, Y. Huang, and W. Li, Compos. Sci. Technol. 65, 1069 (2005).
365K. G. Gatos, A. A. Apostolov, J. Karger-Kocsis, Mater. Sci. Forum 482, 347 (2005).
366S. J. Ahmadi, Y. Huang, and W. Li, Iranian Polym. J. 13, 415 (2004).
367K. Lee, and L. A. Goettler, Polym. Eng. Sci. 44, 1103 (2004).
368H. Zheng, Y. Zhang, Z. Peng, and Y. Zhang, Polym. Polym. Compos. 12, 197 (2004).
369H. Zheng, Y. Zhang, Z. Peng, and Y. Zhang, Polym. Testing. 23, 217 (2004).
370Y. Chang, Y. Yang, and C. Nah, Polym. Mater. Sci. Eng. 84, 591 (2001).
371Y. Chang, Y. Yang, and C. Nah, Abstracts of Papers, 221st ACS National Meeting, San Diego, CA, United States, April,
2001.
372A. Mousa, Polym.-Plast. Technol. Eng. 45, 911 (2006).
373B. Liu, Q. Ding, J. Zhang, B. Hu, and J. Shen, Polym. Compos. 26, 706 (2005).
374Y. Mohammadpour, and A. A. Katbab, J. Appl. Polym. Sci. 106, 4209 (2007).
375H. Zheng, Y. Zhang, Z. Peng, and Y. Zhang, Polym. Polym. Compos. 13, 53 (2005).
376H. Acharya, S. K. Srivastava, and A. K. Bhowmick, Polym. Eng. Sci. 46, 837 (2006).
377D. Kang, D. Kim, S. H.Yoon, D. Kim, C. Barry, and J. Mead, Macromol. Mater. Eng. 292, 329 (2007).
378H. Acharya, S. K. Srivastava, and A. K. Bhowmick, Nanoscale Res. Lett. 2, 1 (2007).
379M. Kato, A. Tsukigase, H. Tanaka, A. Usuki, I. Inai, J. Polym. Sci., Part A: Polym. Chem. 44, 1182 (2006).
380Y. Lu, Y. Liang, Y. Wu, and L. Zhang, Macromol. Mater. Eng. 291, 27 (2006).
381Y. Liang, J. Ma, Y. Lu, Y. Wu, L.Zhang, and Y. Mai, J. Polym. Sci., Part B: Polym. Phys. 43, 2653 (2005).
466 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

382M. Maiti, S. Sadhu, and A. K. Bhowmick, J. Appl. Polym. Sci. 96, 443 (2005).
383A. H. Tsou, and M. B. Measmer, RUBBER CHEM. TECHNOL. 79, 281 (2006).
384A. J. Dias, C. Gong, W. Weng, D. Y. Chung, and A. H. Tsou, (for Exxon Mobil Chemical Patents Inc.) PCT Int. Appl.,
WO02100935, Dec. 19, 2002.
385W. Weng, A. J. Dias, K. R. Karp, M. W. Johnston, C. Gong, C. Neagu, and B. J. Poole, (for Exxon Mobil Chemical
Patents Inc.) PCT Int. Appl. WO2007064400, June 07, 2007.
386S. Takahashi, H. A. Goldberg, C. A. Feeney, D. P.Karim, M. Farrell, K. O’Leary, and D. R. Paul, Polymer 47, 3083
(2006).
387T. Takashima, (for Nippon Petrochemicals Co., Ltd.) Japanese Patent JP2005068237, March 17, 2005.
388M. Maiti, S. Sadhu, and A. K. Bhowmick, J. Appl. Polym. Sci. 101, 603 (2006).
389H. Liao, and C. Wu, J. Appl. Polym. Sci. 97, 397 (2005).
390Y. Chang, D.Lee, and S. Bae, Polym. Int. 55, 184 (2006).
391Y. Kim, and J. L. White, ANTEC 2004 Plastics: Annual Technical Conference, Volume 3: Special Areas, 62nd Annual
Technical Conference - Society of Plastics Engineers, 3, 3798 (2004).
392M. H. Yeh, and W. S. Hwang, Materls. Transctns. 47, 2753 (2006).
393M. H. Yeh, W. S. Hwang, and L. R. Cheng, Appl. Surf. Sci. 253, 4777 (2007).
394K. Sunada, N. Hirashima, K. Takenaka, and T. Shiomi, (for Denki Kagaku Kogyo Co., Ltd.,) Japanese Patent
JP2004189920 A, July 8, 2004.
395S. Kar, and A. K. Bhowmick, IIT Kharagpur, unpublished data, 2007.
396B. B. Marosfoi, G. J. Marosi, A. Szep, P. Anna, S. Keszei, B. J. Nagy, H. Martvonova, and I. E. Sajo, Polym. Adv.
Technol. 17, 255 (2006).
397G. Beyer, Polym. Adv. Technol. 17, 218 (2006).
398T. Mandalia, F. Bergaya, J. Phys. Chem. Solids 67, 836 (2006).
399P. Fang, Z. Chen, S. Zhang, S. Wang, L. Wang, and J. Feng, Polym. Int. 55, 312 (2006).
400S. K. Srivastava, M. Pramanik, and H. Acharya, J. Polym. Sci., Part B: Polym. Phys. 44, 471 (2006).
401W. Zhang, and Y. Fang, J. Appl. Polym. Sci. 98, 2532 (2005).
402B. N. Jang, M. Costache, and C. A. Wilkie, Polymer 46, 10678 (2005).
403S. Peeterbroeck, M. Alexandre, R. Jerome, and P. Dubois, Polym. Degrad. Stab. 90, 288 (2005).
404M. C. Costache, D. D. Jiang, and C. A. Wilkie, Polymer 46, 6947 (2005).
405F. Gao, G. Beyer, and Q. Yuan, Polym. Degrad. Stab. 89, 559 (2005).
406M. Okoshi, and H. Nishizawa, Fire Mater. 28, 423 (2004).
407M. Zanetti, T. Kashiwagi, L. Falqui, and G. Camino, Chem. Mater. 14, 881 (2002).
408H. Nishioka, K. Niihara, T. Kaneko, J. Yamanaka, T. Inoue, T. Nishi, and H. Jinnai, Compos. Interfaces 13, 589 (2006).
409R. K. Gupta, V. Pasanovic-Zujo, and S. N. Bhattacharya, J. Non-Newtonian Fluid Mech. 128, 116 (2005).
410D. S. Chaudhary, R. Prasad, R. K. Gupta, and S. N. Bhattacharya, Polym. Eng. Sci. 45, 889 (2005).
411D. S. Chaudhary, R. Prasad, R. K. Gupta, and S. N. Bhattacharya, Thermochimica Acta 433, 187 (2005).
412S. Peeterbroeck, M. Alexandre, J. B. Nagy, C. Pirlot, A. Fonseca, N. Moreau, G. Philippin, J. Delhalle, Z. Mekhalif,
R. Sporken, G. Beyer, and P. Dubois, Compos. Sci. Technol. 64, 2317 (2004).
413H. O. Pastore, A. Frache, E. Boccaleri, L. Marchese,and G. Camino, Macromol. Mater. Eng. 289, 783 (2004).
414M. Pramanik, H. Acharya, and S. K. Srivastava, Macromol. Mater. Eng. 289, 562 (2004).
415Y. Tian, H. Yu, S. Wu, G. Ji, and J. Shen, J. Mater. Sci. 39, 4301 (2004).
416V. Pasanovic-Zujo, R. K. Gupta, and S. N. Bhattacharya, Rheol. Acta 43, 99 (2004).
417Y. Tang, Y. Hu, J. Wang, R. Zong, Z. Gui, Z. Chen, Y. Zhuang, and W. Fan, J. Appl. Polym. Sci. 91, 2416 (2004).
418W. Zhang, D. Chen, Q. Zhao, and Y. Fang, Polymer 44, 7953 (2003).
419M. Pramanik, S. K. Srivastava, B. K. Samantaray, and A. K. Bhowmick, Macromol. Res. 11, 260 (2003).
 ELASTOMER NANOCOMPOSITES 467

420M. Pramanik, S. K. Srivastava, B. K. Samantaray, and A. K. Bhowmick, J. Appl. Polym. Sci. 87, 2216 (2003).
421X. Li, and C. Ha, J. Appl. Polym. Sci. 87, 1901 (2003).
422M. Alexandre, G. Beyer, C.Henrist, R. Cloots, A. Rulmont, R. Jerome, and P. Dubois, Chem. Mater. 13, 3830 (2001).
423T. Kuila, H. Acharya, S. K. Srivastava, and A. K. Bhowmick, J. Appl. Polym. Sci. 104, 1845 (2007).
424F. Dietsche, Y.Thomann, R.Thomann, and R. M. lhaupt, J. Appl. Polym. Sci. 75, 396 (2000).
425H. R. Jung, M. S. Cho, J. H. Ahn, J. D. Nam, and Y. Lee, J. Appl. Polym. Sci. 91, 894 (2004).
426C. S. Wu, and H. T. Liao, J. Polym. Sci., Part B: Polym. Physics 41, 351 (2003).
427W. F. Lee, and Y. C. Chen, J. Appl. Polym. Sci. 91, 2934 (2004).
428J. Lin, J. Wu, Z. Yang, and M. Pu, Macromol. Rapid Commun. 22, 422 (2001).
429Z. Zhang, N. Zhao, W. Wei, D. Wu, and Y. Sun, Int. J. Nanosci. 5, 291 (2006).
430Y. Xu, and W. J. Brittain, J. Appl. Polym. Sci. 101, 3850 (2006).
431S. Patel, A. Bandyopadhyay, V. Vijayabaskar, and A. K. Bhowmick, J. Mater. Sci. 41, 927 (2006).
432S. Patel, A. Bandyopadhyay, V. Vijayabaskar, and A. K. Bhowmick, Polymer 46, 9079 (2005).
433S. Patel, A. Bandyopadhyay, A. Ganguly, and A. K. Bhowmick, J. Adhes. Sci. Technol. 20, 371 (2006).
434A. Bandyopadhyay, M. Maiti , and A. K. Bhowmick, Mater. Sci. Technol. 22, 818 (2006).
435A. Bandypadhyay, A. K. Bhowmick, and M. De Sarkar, J. Appl. Polym. Sci. 93, 2579 (2004).
436A. Bandyopadhyay, M. De Sarkar, and A. K. Bhowmick, Polym. Polym. Comp. 13, 429 (2005).
437S. Wang, C. Long, X. Wang, Q. Li, and Z. Qi, J. Appl. Polym. Sci. 69, 1557 (1998).
438J. Ma, Z. Yu, H. Kuan, A. Dasari, and Y. Mai, Macromol. Rapid Commun. 26, 830 (2005).
439Q. Kong, Y. Hu, L. Song, Y. Wang, Z. Chen, and W. Fan, Polym. Adv. Technol. 17, 463 (2006).
440J. Wang, Y. Chen, and Q. Jin, High Perfrmnc. Polym. 18, 325 (2006).
441T. C. Chao, G. T. Burns, and D. E. Katsoulis, Polym. Mater. Sci. Eng. 82, 266 (2000).
442J. P. Lewicki, D. Hayward, J. J. Liggat, and R. A. Pethrick, Polym. Preprints 47, 1135(2006).
443L. Yang, Y. Hu, H. Lu, and L. Song, J. Appl. Polym. Sci. 99, 3275 (2006).
444M. J. Jiang, Z. M. Dang, and H. P. Xu, Appl. Phys. Lett. 89, 182902/1 (2006).
445G. W. Lee, J. I. Lee, S. S. Lee, M. Park, and J. Kim , J. Mater. Sci. 40, 1259 (2005).
446J. Paul, S. Sindhu, M. H. Nurmawati, and S. Valiyaveettil, Appl. Phys. Lett. 89, 184101/1 (2006).
447A. H. El-Hag, L. C. Simon, S. H. Jayaram, and E. A. Cherney, Annual Report - Conference on Electrical Insulation
and Dielectric Phenomena, 688 (2004).
448M. Di, S. He, R. Li, and D.Yang, Nuclear Inst. Methods Phys. Res. B 252, 212 (2006).
449D. W. Kang, and H. G. Yeo, J. Indust. Eng. Chem. 11, 567 (2005).
450S. Kolev, A. Yanev, and I. Nedkov, Physica Status Solids (c) 3, 1308 (2006).
451K. S. Giesfeldt, R. M. Connatser, M. A. De Jesus, N. V. Lavrik, P. Dutta, and M. Sepaniak, Appl. Spectroscopy 57,
1346 (2003).
452S. K. Lim, S. T. Lim, H. B. Kim, I. Chin, and H. J. Choi, J. Macromol. Sci., Phys. B42, 1197 (2003).
453R. Valsecchi, M. Vigano, M. Levi, and S. Turri, J. Appl. Polym. Sci. 102, 4484 (2006).
454M. A. Kader, M. Lyu, and C. Nah, Compos. Sci. Technol. 66, 1431 (2006).
455M. A. Kader, and C. Nah, Polymer 45, 2237 (2004).
456M. Maiti, and A. K. Bhowmick, J. Appl. Polym. Sci. 101, 2407 (2006).
457M. Maiti, and A. K. Bhowmick, J. Appl. Polym. Sci. 105, 435 (2007).
458M. Maiti, S. Mitra, and A. K. Bhowmick, Polym. Degrad. Stab. 93,188 (2008).
459T. Lan, P. D. Kaviratna, and T. J. Pinnavaia, Chem. Mater. 6, 573 (1994).
460X. Ma, H. Lu, G. Liang, and H.Yan, J. Appl. Polym. Sci. 93, 608 (2004).
461V. Y. Kramarenko, T. A. Shantalil, I. L. Karpova, K. S. Dragan, E. G. Privalko, V. P. Privalko, D. Fragiadakis, and P.
Pissis, Polym. Adv. Technol. 15, 144 (2004).
468 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

462Z. Wang, and T. J. Pinnavaia, Chem. Mater. 10, 3769 (1998).

463T. K. Chen, Y. I. Tien, and K. H.Wei, J. Polym. Sci., Part A: Polym. Chem. 37, 2225 (1999).
464Y. I. Tien, and K. H. Wei, Polymer 42, 3213 (2001).
465K. J. Yao, M. Song, D. J. Hourston, and D. Z. Luo, Polymer 43, 1017 (2002).
466R. Xu, E. Manias, A. J. Snyder, and J. J. Runt, Biomed. Mater. Res. 64A, 114 (2003).
467M. Bertoldo, S.Bronco, P. Narducci, S. Rossetti, and M.Scoponi, Macromol. Mater. Eng. 290, 475 (2005).
468A. Rehab, and N. Salahuddin, Materls. Sci. Eng. A 399, 368 (2005).
469T. Rihayat, M. Saari, A. R. Suraya, H. M. Mahmood, K. Z. H. M. Dahlan, W. M. Z. W. Yunus, and S. M. Sapuan,
Polym.-Plastics Technol. Eng. 45, 1323 (2006).
470D. Marchant, J. H. Koo, R. L. Blanski, E. H. Weber, P. N. Ruth, A. Lee, and C. E. Schlaefer, PMSE Preprints 91, 32
(2004).
471G. C. Psarras, K. G. Gatos, and J. Karger-Kocsis, J. Appl. Polym. Sci. 106, 1405 (2007).
472J. Xiong, Z. Zheng, X. Qin, M. Li, H. Li, and X. Wang, Carbon 44, 2701 (2006).
473B. Guiffard, L. Seveyrat, G. Sebald, and D. Guyomar, J. Phys. D: Appl. Phys. 39, 3053 (2006).
474P. K. Maji, P. K. Guchhait and A. K. Bhowmick, paper #12B, p.62, Proceedings of India International Rubber
Conference & Expo, Udaipur, India, November, 2007.
475A. Pattanayak, and S. C. Jana, Polymer 46, 3394 (2005).
476A. Pattanayak, and S. C. Jana, Polymer 46, 3275 (2005).
477A. Pattanayak, and S. C. Jana, Polym. Eng. Sci. 45, 1532 (2005).
478F. Cao, and S. C. Jana, Polymer 48, 3790 (2007).
479A. Ganguly, M. ousumi De Sarkar, and A. K. Bhowmick, J. Appl. Polym. Sci. 100, 2040 (2006).
480S. T. Lim, C. H. Lee, Y. K. Kwon, and H. J. Choi, J. Macromol. Sci., Physics B43, 577 (2004).
481C. Lee, S. Lim, Y. C. Kwon, and J. Hyoung, Polym. Preprints 44, 825 (2003).
482S. Lietz, K. W. Sandler, E. Bosch, and V. Altstadt, Kautsch. Gummi Kunstst. 59, 388 (2006).
483T. Yamaguchi, and E.Yamada, Polym. Int. 55, 662 (2006).
484S. Lietz, J. L. Yang, E. Bosch, J. K. W. Sandler, Z. Zhang, and V. Altstaedt, Macromol. Mater. Eng. 292, 23 (2007).
485A. Ganguly and A. K. Bhowmick, 170th Meeting Rubber Division, ACS at Cincinnati, OH, USA, October, 2006.
486J. P. Phillips, X. Deng, R. R. Stephen, E. L. Fortenberry, M. L. Todd, D. M. McClusky, S. Stevenson, R. Misra, S.
Morgan, and T. E. Long, Polymer 48, 6773 (2007).
487M. Liao, J. Zhu, H. Xu, Y. Li, and W. Shan, J. Appl. Polym. Sci. 92, 3430 (2004).
488T. Kwee, and K. A. Mauritz, Polym. Preprints 44, 1106 (2003).
489G. S. Rajan, K. A. Mauritz, S. L. Stromeyer, T. Kwee, P. Mani, J. L. Weston, D. E. Nikles, and M. Shamsuzzoha, J.
Polym. Sci., Part B: Polym. Phys. 43, 1475 (2005).
490M. Maiti, A. Bandyopadhyay, and A. K. Bhowmick, J. Appl. Polym. Sci. 99, 1645 (2006).
491J. Patel, M. Maiti, K. Naskar, and A. K. Bhowmick, Polym. Polym. Comp. 14, 515 (2006).
492I. Gonzalez, J. I. Eguiazabal, and J. Nazabal, Euro. Polym. J. 42, 2905 (2006).
493W. Dong, X. Zhang, Y. Liu, Q. Wang, H. Gui, J. Gao, Z. Song, J. Lai, F. Huang, and J. Qiao, Polymer 47, 6874 (2006).
494H. Thakkar, and L. A. Goettler, Rubber World 229, 44 (2003).
495M. Frounchi, S. Dadbin, Z. Salehpou, and M. Noferesti, J. Mem. Sci. 282, 142 (2006).
496S.Tembhekar, M. Maiti, A. Biswas, J. J. Geroge, A. K. Bhowmick, M. Swaroop, and A. Biswas, paper #C-16, p. 96,
Proceedings of International Conference on Rubber and Rubber like Materials, Kharagpur, India, January 2008.
497P. Chakraborty, A. Ganguly, S. Mitra, and A. K. Bhowmick, paper #C-08, p. 58, Proceedings of International
Conference on Rubber and Rubber Like Materials, Kharagpur, India, January 2008.
498R. Lamba, paper #26A, p.78, Proceedings of India International Rubber Conference & Expo, Udaipur, India,
November, 2007.
 ELASTOMER NANOCOMPOSITES 469

499M. A. Sharaf, and J. E. Mark., Polymer 45, 3943 (2004).

500A. Kloczkowski, M. A. Sharaf, and J. E. Mark, Chem. Eng. Sci. 49, 2889 (1994).
501Q. W. Yuan, A. Kloczkowski, J. E. Mark, and M. A. Sharaf, J. Polym. Sci. Part B: Polym. Phys. 34, 1647 (1996).
502G. A. Buxton, and A. C. Balazs, J. Chem. Phys. 117, 7649 (2002).
503E. Chabert, R. Dendievel, C. Gauthier, and J. Y. Cavaille, Compos. Sci. Technol. 64. 309 (2004).
504G. Raos, M. Moreno , and S. Elli, Macromolecules 39, 6744 (2006).
505M. Bhattacharya and A. K. Bhowmick, communicated to Polymer, 2008.
506N. Sheng, M. C. Boyce, D. M. Parks, G. C. Rutledge, J. I. Abes, and R. E. Cohen, Polymer 45, 487 (2004).
507Q. H. Zeng, A. B. Yu, and G. Q. Lu, Prog. Polym. Sci. 33, 191 (2008).
508Doug Brown, "Nano Litterbugs? Experts See Potential Pollution Problem," Small Times, March 15, 2002.
509A. Huczko, H. Lange, E. Cako, H. Grubek-Jaworska, and P. Droszcz, Fullerene Nanotubes and Carbon
Nanostructures 9, 251 (2001).
510S. Fiorito, A. Serafino, F. Andreola, and P. Bernier, Carbon 44, 1100 (2006).
511J. Gorman, "Taming High-Tech Particles: Cautious Steps into the Nanotech Future," Science News Online, March 30,
2002; available on the Internet:www.sciencenews.org/20020330/bob8.asp, access date 04.04.2008.
512G. Whitesides, and J. C. Love, "The Art of Building Small," Scientific American 285, 38 (September, 2001).
513http://www.apnf.org/content.php?content.htm1, access date 04.01.2008.
514http://cordis.europa.eu/nanotechnology/home.html, access date 04.04.2008.
515http://www.nanotechproject.org/7/mission, access date 04.10. 2007.
516A. Huczko, and H. Lange, Fullerene Nanotubes Carbon Nanostructures 9, 247 (2001).
517http://www.nanotec.org.uk/finalReport.htm, access date 04.04.2008.
518http://www.epa.gov/osa/nanotech.htm, access date 04.04.2008.
519http://www.nanocompositech.com/commercial-nanocomposites-nanoclays.htm, access date 04.04.2008.

[ Received April 2008 ]