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Rubber Nanocomposites: Latest Trends and Concepts


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Rubber nanocomposites have a unique position both in academic and industrial point of view and extensive research studies are progressing in this area. Due to their ever increasing significance, a thorough investigation is necessary especially when the application side is considered. The enhanced surface area and high aspect ratio of nano materials lead to superior matrix/filler interaction and this results in the versatile properties and wide range of applications for the obtained nanocomposites. Nano fillers like layered silicates, carbon nanotubes (CNTs), fullerenes, silica, metallic nanoparticles, metal oxides, polyhedral oligomeric silsesquioxane (POSS), biomaterials, nanodiamonds etc. are used extensively in rubber composites fabrication. In this chapter, attempt has been made to briefly explain the recent advances in the area of nanofillers and their rubber nanocomposites. A thorough survey has been made by giving special emphasis to the filler geometry and composite morphology on one side and the composite properties on the other. Finally the study ends up with novel applications of rubber nanocomposites and the future perspectives in this area.
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Rubber Nanocomposites: Latest Trends
and Concepts
Deepalekshmi Ponnamma, Hanna J. Maria, Arup K. Chandra
and Sabu Thomas
Abstract Rubber nanocomposites have a unique position both in academic and
industrial point of view and extensive research studies are progressing in this area.
Due to their ever increasing significance, a thorough investigation is necessary
especially when the application side is considered. The enhanced surface area and
high aspect ratio of nano materials lead to superior matrix/filler interaction and this
results in the versatile properties and wide range of applications for the obtained
nanocomposites. Nano fillers like layered silicates, carbon nanotubes (CNTs),
fullerenes, silica, metallic nanoparticles, metal oxides, polyhedral oligomeric
silsesquioxane (POSS), biomaterials, nanodiamonds etc. are used extensively in
rubber composites fabrication. In this chapter, attempt has been made to briefly
explain the recent advances in the area of nanofillers and their rubber nanocom-
posites. A thorough survey has been made by giving special emphasis to the filler
geometry and composite morphology on one side and the composite properties on
the other. Finally the study ends up with novel applications of rubber nanocom-
posites and the future perspectives in this area.
Aspect ratio
AFM Atomic force microscopy
CB Carbon black
CNT Carbon nanotube
CVD Chemical vapor deposition
D. Ponnamma (&) H. J. Maria S. Thomas
School of Chemical Sciences, Mahatma Gandhi University, Kottayam, Kerala 686560, India
S. Thomas
Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam,
Kerala 686560, India
A. K. Chandra
R&D Centre, Apollo Tyres Ltd., Limda, Waghodia, Vadodara, Gujarat 391760, India
P. M. Visakh et al. (eds.), Advances in Elastomers II,
Advanced Structured Materials 12, DOI: 10.1007/978-3-642-20928-4_3,
Ó Springer-Verlag Berlin Heidelberg 2013
CRG or GE Chemically reduced graphene
EG Expanded graphite
GO Graphene oxide
HR-TEM High resolution-transmission electron microscopy
MMT Montmorillonite
NR Natural rubber (poly isoprene)
NBR Nitrile–butadiene rubber
XNBR Carboxylated nitrile–butadiene rubber
PDMS Polydimethylsiloxane
RTVSR Room temperature vulcanizing silicone rubber
RGO Reduced graphene oxide
SWCNT Single wall carbon nanotube
SEM Scanning electron microscopy
SDS Sodium dodecyl sulfonate
SR Silicone rubber
SBR Styrene–butadiene rubber
TEM Transmission electron microscopy
TRG Thermally reduced graphene
TPU Thermoplastic polyurethane
1 Introduction
Rubbers an important class of polymers, generally known as elastomers are useful
materials from the time immemorial. It is a very essential material in industry due
to their unique properties particularly viscoelasticity. For making them applicable
in various fields, fillers are added to it resulting in the manufacture of varieties of
composites. This will impart high elastic moduli and durability for the elastomers,
which were always limiting their practical usage. Mineral fillers are known to
improve the strength and stiffness of rubbers. However the extent of property
enhancement depends on various factors such as the size and shape of the particles,
filler aspect ratio, degree of dispersion and orientation of particles in the matrix
and the interfacial adhesion between filler and polymer chains [1]. In general, it is
said that the filler–filler [24] and the filler-rubber interactions [5] cause better
reinforcement. The nano materials with average particle size in the range of
1–100 nm are extremely useful polymeric reinforcements. Compared to traditional
fillers, these particles can enhance the composite properties in relatively small
concentrations. In the nano-scale regime, some materials exhibit additional or
different features or properties as compared to coarser materials. These materials
are now used in a wide range of innovative technological applications and prod-
ucts. Nano sized fillers have the unique ability to form very fine and homogenous
70 D. Ponnamma et al.
dispersion in the elastomer matrices and occupy substantially greater number of
sites in it. In general, nanocomposite manufacturing processes include in situ
polymerization, solution mixing and melt compounding [69].
Among the nonblack fillers, layered silicates are very useful due to the low cost,
versatility, availability and stiffening properties. Clays contain hexagonal platelets
having thickness in the nanometer range, and length and breadth in the micro
range. But, when compared to the carbon black fillers, clay filled composites
exhibit less mechanical properties since the hydrophilicity of clay causes poor
filler/polymer interaction. This as well as the slow curing effect observed in clay
systems can be avoided by the organic modification of clay platelets. Apart from
the mechanical and thermal applications, clay composites are used in tyre inner
liners where they are helpful in reducing the air permeability. The reason for this
behavior is the formation of tortuous paths by the gas molecules due to orientation
of filler platelets, and thus causing the air permeability of the composite to
decrease. More recently, extensive studies using fillers like carbon nanotubes,
graphene etc. are going on other than clay [10].
Carbon nanotubes (CNTs) are made of cylindrical graphitic sheets with fullerene
end-caps [11], diameter ranging from 1 to 100 nm and length up to several milli-
metres. Its density varies between 1 and 2 g/cm
and modulus is greater than 1 TPa
[12]. Based on the structure, there are single walled (SWCNT) and multi walled
(MWCNT) nanotubes and both are widely used as nanofillers. Recently graphite and
its derivatives like graphite oxide (GO) are noted for their high dispersive capacity,
long coherence length and superior barrier properties [13, 14]. High conductivity of
these fillers make them applicable in electronics for instance in sensor skins [15, 16],
flexible display [1719], and in dielectric actuators [2022] instead of the brittle
material based systems currently used. Polyhedral oligomeric silsesquioxanes
(POSS) having combined organic/inorganic material properties are excellent
lightweight, high performance hybrid materials used to modify many polymer
properties [23]. Having 1–3 nm diameter, POSS can enhance the service tempera-
tures, decomposition temperatures, oxidation resistance, surface hardening,
mechanical properties, flame retardancy, heat evolution [24] etc. of several poly-
meric materials to a great extent. Very recently, bionanofibers and their nano crystals
obtained from natural resources as reinforcing agents in several polymeric matrices
have attracted the attention of researchers. Bionanofibers include nanocellulose,
nanochitin and nanostarch and their nanocrystals. This chapter deals with fillers
having various morphologies such as layered sheets (montmorillonite, hectorite, and
graphene), cylindrical tubes (carbon nanotubes,) and spherical particles (such as
POSS) and their rubber nanocomposites.
Amidst of the superior properties imparted by the nano fillers, their incom-
patibility due to poor dispersion in the polymer matrix cannot be neglected. This is
the most important problem faced by the material scientists. The interfacial
strength between the filler and polymer is another important aspect which should
be given due consideration. The poor filler-polymer adhesion cause the formation
of nanoparticle aggregates during the composite fabrication, which is responsible
for failure at the interface and for the decreased physical as well as chemical
Rubber Nanocomposites: Latest Trends and Concepts 71
properties of the final composites. The nano particle aggregation can be minimized
to a great extent by modifying the filler surface either chemically or physically.
This can regulate the reaction rate [25] as well. In addition to the information
about various kinds of fillers special emphasis has been given in discussing about
the composite manufacturing techniques, properties of composites and their ver-
satile applications in this survey, by addressing filler dispersion problems and their
modification methods.
2 Nanofillers
Generally, fillers are solid particulate materials (inorganic, organic) that have
irregular, spherical, fibrous, or platelet-like shape. Whereas a nano-filler (exist in
defined singular form that have at least one dimension in the nano scale, \100 nm)
impart properties as desired and can be tailor made according to the individual
needs. As already mentioned, such nanofillers at small percentages (\10 %) can
improve polymer properties such as heat resistance, barrier properties, strength,
stiffness, flame retardancy etc. The small particle size (size range 1–100 nm), high
specific surface area and hence the high surface area-to-volume ratio of nano fillers
change the reactivity and physical properties of the elastomers without affecting its
bulk properties like density or light transmission. The enhanced surface area to-
volume ratio also helps nanoparticles to interact with one another in different
ways. Nano fillers improve mechanical or physical properties of elastomers sig-
nificantly, reduce the material cost and increase the processability [26]. One of the
biggest rubber industries, the tyre manufacturing units, use fillers like nano-silica,
nano-zinc oxide, nano-black, etc. for performance improvement. This increase in
properties may be attributed to the chemical bond formation, disruption of the
elastomer conformational position and orientation of polymer chains and the
immobilization of adjacent polymer chains.
Based on the number of dimensions in nano scale, nano fillers can be classified
into three types—One-dimensional (one dimension in nanometer scale, usually the
thickness, e.g. plates or laminas layered silicates, layered double hydroxides
(LDHs)), two dimensional (two dimensions in the nanometer scale and the third a
little longer (nanotubes and nano fibres) and three-dimensional (nanogranules,
nanocrystals and spherical for instance POSS, nano silica)—[28, 29] as illustrated
in Fig. 1. All these kinds of nano fillers possess different surface properties than
bulk due to their large surface area facilitating large volume of interfacial matrix
material. As we move from macro to micro to nano-materials, nano sized materials
have new and surprising important properties related to solubility, reactivity,
selectivity, optical, electrical, magnetic and mechanical properties. Among nano-
materials, nano-clays are the most commonly used commercial additive for the
preparation of nano-composites, accounting for nearly 80 % of the volume used.
Since the interface between fillers and rubber is one of the factors determining the
composite properties, a comparative study has been done on the variation of the
72 D. Ponnamma et al.
interfacial volume of polymers with filler dimensions [30]. The three general
categories of nano fillers—tube like (diameter \100 nm and an aspect ratio of at
least 100), plate-like (thickness on the order of 1 nm, aspect ratio in the other two
dimensions of at least 25) and sphere like (\100 nm dimension)—changes the
interfacial interaction significantly as shown in Fig. 2. An increase in interfacial
volume with decreasing nanoparticle size is clearly evidenced from the plot.
A few of the numerous nano materials useful in rubber reinforcement are
discussed below:
2.1 Nano-Clays
Layered silicates or clays come under the class of hybrid organic–inorganic
nanocomposites [32, 33]. These are the most widely used reinforcement due to
their natural abundance and high aspect ratio. They contain two structural units—a
silica tetrahedral sheet fused to an aluminum octahedron—by sharing oxygen
atoms. Since the clays have surface charges, they are highly hydrophilic, making it
less compatible with a wide range of non polar elastomers. This can be solved by
adding certain surfactants or covalently modifying the surface of the clay sheets,
which leads to the formation of the so called organically modified clays (OMMTs).
Fig. 1 Various types of nanoscale materials [27]
Fig. 2 Plot of volume of
interfacial polymer based on
10 nm thick interfacial region
surrounding each
nanoparticle against volume
fraction [31]
Rubber Nanocomposites: Latest Trends and Concepts 73
Out of these organically modified Montmorillonite is the most used one. There are
numerous studies on the incorporation of nano-clays into natural rubber [3436],
styrene-butadiene rubber [3740], brominated isobutylene-co-p-methylstyrene
[41], ethylene-propylene-diene rubber [42], epoxidised natural rubber [43, 44], and
blends thereof [4446]. Clay nanocomposites are excellent flame retardants and
exhibit improved gas barrier properties.
2.2 Nano-Oxides
Amongst the existing activator system, zinc oxide (ZnO) has been widely used as
the most cost-effective ingredient and improves the processability and the physi-
cal, mechanical and thermal properties of the rubber [47, 48] especially in the tyre
industry. But, there are environmental concerns over the harsh influence of Zn-
based materials on human health and ecological systems. This reason has
prompted the rubber manufacturers to proactively evaluate the strategies for zinc
content reduction in rubber formulations by mixing nano-ZnO [49].
2.3 Carbon Nanotubes
Carbon nanotubes (CNTs) also been considered as an attractive candidates for
imparting several properties to elastomers. A carbon nanotube is a tube-shaped
material, made of carbon, having a diameter measuring on the nano-meter scale.
Carbon nanotubes have many structures, differing in length, thickness, and in the
type of helicity and number of layers. Commonly used nanotubes are single-walled
nanotubes (SWCNTs) and multi-walled nanotubes (MWCNTs). SWNTs contain
one cylinder formed by wrapping one layer of graphene sheet and MWNTs by
several layers. The diameter of SWCNTs is close to 1 nm, whereas for MWNTs, it
varies up to 100 nm. Structure of CNTs is well understood from the TEM images
given in Fig. 3. Although they are formed from essentially the same graphitic
sheet, their electrical characteristics differ depending on these variations, acting
either as metals or as semiconductors. CNTs improve the electrical as well as
thermal conductivity of elastomers. The electrical properties of CNTs are signif-
icant and considered to be very important in the tyre industry as a source for
dissipating static charge. Replacing the carbon black by carbon nanotubes
improved skid resistance and reduced abrasion of the tire [50]. Carbon nanotubes
may provide a safer, faster, and eventually cheaper transportation in the future
[51]. CNTs themselves are superior conductors but they may not exhibit the same
level of conductivity, when integrated into other materials [52].
74 D. Ponnamma et al.
2.4 Graphene
In addition to CNTs, the one atom thick two-dimensional graphene sheet can also
provide effective reinforcement to elastomers. In graphene, the sp2-hybridized
carbons are arranged like a honeycomb structure, which can provide huge surface
area (experimentally 1850 m
) since because of the availability of both sides
of the sheets [54]. Graphenes have the unique capacity of enhancing the thermal,
electrical and gas barrier properties. The two dimensional sheets of graphite,
expanded graphite, graphene oxides, graphite oxides etc. are also widely used in
regulating the polymer properties.
2.5 Polyhedral Oligomeric Silsesquioxane
Polyhedral oligomeric silsesquioxane (POSS) is the recent development in poly-
mer science and technology. The three dimensional POSS molecules are consid-
ered as the smallest particles possible for silica and they consists of an inorganic
silica Rn(SiO
)n core cage structure where n is the number of silicon atoms of the
cage (n = 8, 10, 12) with diameter less than 3 nm and mass about 1000D. This
enables POSS to get nearly equivalent dimensions of polymers, with less radius of
gyration than polymer chains and thereby applicable in tremendous polymer
nanocomposites. Several structural representations of silsesquioxanes with the
empirical formula RSiO
are possible, with the two most common representa-
tions being a ladder-type structure and a Si-O cage framework (Fig. 4). There are
reports of using POSS in tyres. In a patent by Crutchley [55] a rubber composition
comprising one or more POSS included in the rubber composition as part of a
rubber compound master batch or added as an additive to a rubber compound
master batch. In another patent [56]; Puhala claimed a rubber composition having
POSS as reinforcement.
Fig. 3 TEM Images of carbon nanotubes a at low resolution b at high resolution [53]
Rubber Nanocomposites: Latest Trends and Concepts 75
2.6 Nano Carbon Black and Nano Silica
The nano-structures carbon black and nano silica are the new category of fillers in
tyre applications. Nano-structured black is a family of new carbon black charac-
terized by a rough surface and enhanced filler-polymer interaction. It hinders the
slippage of polymer molecules along the rough nano-structured surface and
reduces the hysteresis significantly. This type of black ideally meets truck tyre
requirements, as it provides improved tread wear in addition to low hysteresis [58].
Synthesis of nano silica has gained much attention due to its superior properties
and most widely being used as filler in rubber. These silica nano-particles show
superior physico-mechanical properties and improvement in the processing
2.7 Bionanofillers
Over the past two decades much effort have been devoted to the use of micro-
crystals obtained from natural resources as reinforcing agents in several polymeric
matrices. Environmental pollution, depleting oil reserves, oil barrel price evolu-
tion etc. have triggered the need to find bio-based solutions. The advantages of
natural fillers are their low density, renewable character, and biodegradability
associated with the highly specific properties of nanoparticles. Nanosized deriv-
atives of polysaccharides like starch, chitin and cellulose can be synthesized in
Fig. 4 Structural representations of silsesquioxanes [57]
76 D. Ponnamma et al.
bulk and can be used for the development of bionanocomposites. They can be
promising substitutes for environment pollutant carbon black, for reinforcement of
rubbers even at higher loadings (up to 50 phr) via commercially viable process.
The combined effect of size reduction and organic modification improves filler–
matrix adhesion and in turn the performance of bionanofillers. Cellulose, chitin
and starch are abundant, natural, renewable and biodegradable polymers from
where we can prepare cellulosic nanofibers, cellulose nanowhiskers, starch
nanocrystals and chitin nanowhiskers [5970].
2.7.1 Starch Nanoparticles
The use of polysaccharides as reinforcing agents for polymer materials are due to
their properties like renewable nature, availability, diversity of sources, low
density, low energy consumption, low cost, high mechanical properties, compar-
atively easy processability, nonabrasive nature, relatively reactive surface, which
can be used for grafting specific groups etc. Native starch granules contain more or
less concentric ‘growth rings’ that are readily visible by optical or electronic
microscopy. The starch structure has been under research for years, and because of
its complex structure, a universally accepted model still need to be proposed [71].
The structure of starch forms a concentric semicrystalline multiscale structure that
allows the production of new nanoelements like:
(i) starch nanocrystals from the disruption of amorphous domains from semi-
crystalline granules by acid hydrolysis
(ii) starch nanoparticles produced from gelatinized starch.
These starch nanoparticles are proved to improve mechanical and barrier prop-
erties of bionanocomposites when used as fillers. Because of their use in industrial
packaging, researchers are continuously looking for innovative solutions for effi-
cient and sustainable systems. Therefore, starch nanoparticles have been the focus of
an exponentially increasing number of works devoted to develop bionanocompos-
ites by blending starch nanoparticles with different biopolymeric matrices.
2.7.2 Cellulosic Nanoparticles
Being one of the most abundant biomass materials in nature, cellulose allows
different kinds of nanoscale cellulosic fillers—called cellulose nanocrystals or
microfibrillated cellulose (MFC) [72]. Cellulose nanoparticles have been the focus
of an exponentially increasing number of works or reviews devoted to under-
standing such materials and their applications. Over the last decades researchers
have shown that cellulose nanoparticles could be used as fillers to improve
mechanical and barrier properties of biocomposites. The microfibrils, was found to
possess width in the range of 5–30 nm, [72] and are highly crystalline materials
formed by lateral packing of long cellulose molecules with hydrogen bonding.
Rubber Nanocomposites: Latest Trends and Concepts 77
Figure 5 shows the FE-SEM micrographs of cellulose nanofibers. The outstanding
mechanical properties, with a high Young’s modulus of 138 GPa in the crystal
region along the longitudinal direction [73] and a very low coefficient of thermal
expansion along the longitudinal direction [74] was shown by a stable structure.
Therefore, cellulose whiskers and fibrils have great potential for use as rein-
forcement in nanocomposites and have attracted a great deal of interest recently
[7579]. Various conditions and steps involving general synthesis of starch and
cellulosic nanoparticles are represented in Fig. 6 [80].
2.7.3 Chitin Nanowhiskers
Chitin, the animal counter part of cellulose is the second most available material in
nature. In recent years considerable interest has been devoted to biomaterials based
on chitin and on its amino-derivative chitosan. It is estimated that about
1010–1011 tons of this polymer are synthesized each year [81]. Chemically, chitin
molecules consist of N-acetyl-D-glucosamine units. Chitin is known to be non-
toxic, odorless, biocompatible with living tissues, and biodegradable [82] and
hence the application of this as the reinforcing agent is boundless. The advantage
of chitosan over other polysaccharides (cellulose, starch etc.) is that, its chemical
Fig. 5 FE-SEM micrographs of nanofibers [79]
78 D. Ponnamma et al.
structure allows specific modifications without too many difficulties at the C-2
position. Specific groups can be introduced to design polymers for selected
applications [83]. Regardless of the chitin sources, the hydrolytic condition is
commonly-used for obtaining chitin whiskers [8486] Chitin whiskers obtained
from squid pen [87] and Riftiatubes [88] was found to have good reinforcing effect
in copolymer of styrene and butyl acrylate [87] or poly(caprolactone) [88].
2.8 Other Nano-Particles
There are several other nano-particulate materials which are getting attention from
compounders such as nano-calcium carbonate [89], nano-carbon fiber [90], nano-
cellulose [91], nano-mica [92], nano-talc [93], etc. In recent years, there is
development of new nano-particles from different polymers known as core–shell
nano-particles. These nano-particles have a crosslinked core and a crosslinked
shell. Conducting polymers like polyanilines (PAni) are also notable fillers due to
its low cost, good conductivity, stability and easy synthesis. Conducting elastomer
blends of polyanilines and rubbers such as polychloroprene, ethylene-propylene-
diene (EPDM), styrene-butadiene (SBR) rubber, and nitrile rubber (NBR) have
been reported [94101]. These composites showed conductivity values in the
range of 10
to 10
Fig. 6 Different steps
involving general synthesis of
starch and cellulosic
nanoparticles [80]
Rubber Nanocomposites: Latest Trends and Concepts 79
Other nanofillers like alumina (Al
), silica (SiO
) and titania (TiO
) improve
the dielectric properties of the polymers significantly and modification of their
surface can impart much stronger influence on the properties. Nanoparticles like
silica usually exist in the powdered or colloidal [94] form and is obtained by sol–
gel or the microemulsion method [102]. Nanosilica can also be produced by fol-
lowing the fuming method and/or the precipitation method. The white, amorphous
powder of fumed silica is manufactured by a hydrothermal process and it possesses
three kinds of surface hydroxyl groups such as isolated free, SiOH, geminal free,
and vicinal, OH groups bound together through hydrogen bond. This can
help in the better grafting of filler particles on polymer chains. Figure 7 shows the
difference between modified and unmodified alumina and it is clear that modifi-
cation significantly avoids agglomeration of particles and enhances the dispersion.
Filler modification includes treating it with suitable surfactants or chemical
modification on the filler surfaces. Surfactants cause a wrapping effect on the filler
particles thereby reducing their agglomeration tendency. Surfactants can also
decrease the surface tension of the suspension which also helps in particle seg-
regation and well dispersion. Chemical modification always leads to the addition
of functional groups on filler surfaces and helps in making filler polymer covalent
bonds. Even though this method offers better bonding, chemical treatments can
cause filler defects which sometimes cause a negative impact on composite
properties. Nanocomposites are synthesized by incorporating all these kinds of
fillers in suitable matrices (Table 1).
3 Rubber Nanocomposites
Properties of rubber nanocomposites have been greatly influenced by the nature of
filler and rubber, interfacial filler-elastomer interactions, compatibilisation and
mode of dispersion. Among the various fillers used in the fabrication of rubber
nanocomposites, nano silica, carbon nanotubes, graphene, bionanofibers and
Fig. 7 TEM of untreated Al
(a) and KH570-Al
80 D. Ponnamma et al.
nanoclays have unique importance in regulating the properties and are mainly
focused in this survey.
3.1 Preparation Methods
A lot of preparation methods are employed for fabricating the nanocomposites, out
of which the most commonly used techniques are melt mixing, solution casting
and in situ polymerization. Apart from describing these three conventional
methods, effort has been made to point out other methods also. Table 2 illustrates a
few of the various preparation methods applied in the rubber composite
Solvent casting: This technique is based on dispersing the filler as well as the
matrix in suitable solvents separately and then mixing both together. The solvent
evaporates from the casted suspensions to get dried composite samples. Using
ethanol as dispersing agent, Das et al. [111] got good dispersion of CNTs and thus
Table 1 Structural characterization of EG, Graphite nanoplatelets, clay, CNT and graphene
Material Parameters Surface area (m
/g) Electrical conductivity
Clay 100–150 nm [27]
Interlayer spacing
700–900 [27]–
GNP 2–150 nm [104]
15–2630 [104] 5.98 ± 0.11 9 10
(S/m) [105]
Graphene 0.34 nm [106]
*2630 [106] 1.28 ± 0.04 9 10
(S/m) [105]
POSS 1–1.5 nm [107]
500 [107] 6000 S/cm [105]
CNT *1nm[108]
10–20 [108] 5–50 [109]
PAni 50–100 nm [110] 40–50 [110] 3–300 (S/m) [110]
Table 2 A few preparation methods of rubber nanocomposites
Preparation method Composite system Reference
Solvent casting NR latex and clay rectorite [136]
Solution mixing and melt mixing Isobutylene/isoprene rubber/organic modified clay [137]
Masterbatch method NR or SBR/clay and carbon black [138]
Latex stage compounding NR latex/CNT [120]
Hetero coagulation approach SBR/carbon black, CNTs [139]
Melt blending NR/graphene [134]
Solution mixing PU/POSS [140]
Emulsion in situ polymerization Styrene and butyl acrylate and laponite [141]
Melt blending TPU/clay [142]
Electrospinning Quantum dots/elastomer [143]
Rubber Nanocomposites: Latest Trends and Concepts 81
excellent mechanical properties for the composites. Khalid et al. [112] also dis-
persed CNTs in NR via solvent casting method using toluene. Ganter et al. prepared
rubber nanocomposites based on styrene–butadiene rubber (SBR) and butadiene
rubber (BR) containing organophilic-layered silicates [113, 114] by following
solution mixing process. Graphene/rubber nanocomposites are also reported via
solution blending [115117]. Haiqing et al. fabricated [118] silicon rubber/graphene
(and CNTs) composites by solution mixing in THF solvent and obtained excellent
reinforcement. Figure 8 shows a schematic representation of the fabrication of
reduced graphene oxide (RGO) dispersed in NBR composite using the solvent
xylene [119]. The use of solvents like toluene is considered to be the disadvantage of
this technique even if good dispersion can be achieved through this.
Latex stage compounding: Since most of the rubbers also exist in latex form,
this compounding technique is of great significance. This is done by adding the
filler and the curing agents like sulphur, ZnO and stearic acid directly to the latex
and then following the mixing, casting steps as in the solution mixing. This method
has been reported for the fabrication of NR latex/MWCNTs [120, 121] and NR/
10 wt% natural and synthetic layered silicates nanocomposites [120]. Rubber/
Ca-montmorillonite (Ca-MMT) nanocomposites containing well exfoliated
Ca-MMT layers were prepared by a combined latex compounding and melt mixing
[121] technique. NBR/clay composites are synthesized by following continuous
dynamic latex compounding [122]. Graphene/rubber nanocomposites were also
reported by this method [123]. The interaction of CNTs with the latex particles in
Fig. 8 Illustration of preparation of RGO–NBR composite [119]
82 D. Ponnamma et al.
the presence of surfactants are described in the Fig. 9. After casting, well exfoliated
nanotube bundles in the matrix are observed.
In-situ polymerization: In situ polymerization is an effective method to attain
uniform dispersion of fillers in elastomers. Here, the filler is mixed with the
monomer and essential reagents to trigger the polymerization reaction in the
presence or absence of a solvent. During the polymerization reaction, a uniform
dispersion of fillers inside the matrix can be obtained. This will lead to the greater
reinforcement effect through the strong interfacial bonds formed [125, 126]. Ka-
minsky et al. used bis (cyclopentadienyl) zirconium compounds in the presence of
Zeigler catalysts to synthesize atactic poly propylene and further reacted it with
ethylene and diolefines to manufacture EPDM rubber [127]. They also prepared
EPDM terpolymers with ethylidene norbornene as diene monomer using a zir-
conium based Ziegler catalyst [128, 129].
Melt blending/Extrusion: Absence of solvent is considered to be the major
advantage of this method. This process is industrially important and offers mixing
at high temperature and at high shear force. Extruders, internal mixers etc. are used
for this purpose. Melt mixing can result in good dispersion of CNTs in styrene
butadiene (SBR) and butadiene rubber (BR) blend as reported by Das et al. [130].
Vu et al. [131] reported that the compounds of epoxidised natural rubber (ENR)
and sodium MMT clay prepared by melt mixing exhibit higher tensile properties
than those compounds of precipitated silica. Sulfur-cured ENR recipes containing
layered silicates produced by melt compounding were studied by Varghese et al.
[132]. EPDM/nano ZnO composites were fabricated following the same process
Fig. 9 Schematic representation of the surfactant interaction on the surface of CNTs after
sonication, interaction of CNT with latex and subsequent drying of the latex film [124]
Rubber Nanocomposites: Latest Trends and Concepts 83
[133]. Arroyo et al. reinforced NR with 10 phr Na-MMT and ODA-MMT by melt
mixing [134]. Graphene/rubber nanocomposites were also reported via melt
blending [115, 134135].
Simple methods like freeze drying, spray drying, heterocoagulation approach,
pulverization method etc. can also be applied for the composite manufacture.
3.2 Properties of Nanocomposites
Reinforcing fillers for rubber typically have relatively large particle sizes. Such
fillers are commonly inert without any reactive moieties on their surfaces. These
fillers are added to the polymers to promote specific properties and also to reduce
the cost. However, to improve the surface hydrophobicity, electrical conductivity,
thermal conductivity and relative permeability of polymeric materials, micro/
nano-fillers are added. Nanocomposites exhibit enhanced properties compared to
the pristine elastomers. Fillers when exfoliated go to the free spaces in between the
polymer chains and wrap around it. The better the dispersion, the more will be the
reinforcement. This reinforcing effect of clay platelets can be well explained by
the following Fig. 10. Styrene butadiene rubber is the elastomeric co polymer used
here and it is found that the force between the fillers and the matrix balances the
polar, steric and electrostatic contributions due to the nice dispersion of fillers.
Thus, the segments of the polymer chains (butadiene part) are adsorbed on the
kaolin surfaces and pores of the clay aggregates. This enhances the hard part
(styrene) in the matrix and accordingly the elastic constant of rubber enhances
Fig. 10 Schematic
representation of structure of
styrene–butadiene block
copolymer filled with kaolin
powder [144]
84 D. Ponnamma et al.
dramatically when nanoclays are added. The usually addressed properties of all
kinds of nanocomposites such as mechanical strength, rheology, electrical con-
ductivity and gas permeability are discussed here in detail.
3.2.1 Mechanical Properties
The mechanical behavior of elastomer nanocomposites depends on several factors,
including the filler dispersion, degree of interfacial adhesion between elastomers
and fillers and crosslink density of the composite. Mechanical properties of a few
nanocomposites are compared in Table 3.
The tensile strength and elongation at break of NR/SBR/organo clay (OC)
nanocomposites is demonstrated in Fig. 11a, b. The authors correlated tensile
strength with the microstructure of the prepared nanocomposites and found the
influence of compatibilisers on the properties. The compatibilisers, epoxidised
natural rubber (ENR50) and EPDM-g-MAH enhance the strength and stress at 100
and 300 % elongation to a great extent. They obtained highest reinforcement effect
when the compatibilizer to clay ratio was 3 (B4EP3 and B4EN3).
The stress strain curves of Al
/NR nanocomposites with change in filler
loading are shown in Fig. 12. The unique property of strain-induced crystallization
of natural rubber is clearly shown in this curve. The modulus increases with
Table 3 Mechanical Properties of Elastomer/nano filler derivative composites
Elastomer Filler Content Processing Modulus
Elongation at
break (%)
neat polymer)
NR latex
In situ reduction
2 wt% Solution M 300
25.2/17.1 564/579
Melt 2.47/2.4 18.8/17.1 600/579
NR [108] MWCNT:Silica)/
0 phr
3:40 phr Melt 4.8/1 Stress
29/12 470/480
17.2/2.5 299/299
Nano Zno 3 phr Melt 15.87 286
Silica/POSS Constant/ 25 wt%
1.1 100
Clay 10 phr Melt 1.70 11.12 480
Rubber Nanocomposites: Latest Trends and Concepts 85
increase in strain at lower strain region and then sharply increases due to the
development of induced crystallization. When the nanocomposites are considered,
the tensile strength and modulus values are higher than that of pure NR, but the
strain induced crystallization weakens. This is due to the better dispersion of Al
nanoparticles, and the increased force between the nano layers and the NR chain.
Figure 12b shows the tensile properties of NBR composites and it is observed that
the elongation at break and modulus values of NBR/EG/CB (expanded graphite
and carbon black composites) composites is higher than NBR/CB composites.
Carbon black (CB) mainly contributes to rubber reinforcement and along with this,
the higher dispersion of thin graphite sheets lead to significant enhancement in
tensile modulus (at 100 % elongation) and hardness.
The steady increase in the tensile strength with strain is reported in the case of
NBR–nano calcium carbonate (NBR-NCC) composites [149] which are typical for
all synthetic elastomers. The addition of NCC increases stress in the composite for
the same rate of strain and the strength increases with NCC amount. Here, the tensile
Fig. 11 Tensile strength and elongation at break for the NR/SBR simple blend (B), unfilled NR/
SBR blend but containing compatibilizer (BEP2, BEN2), uncompatibilized NR/SBR/OC sample
(B4), and NR/SBR/OC Nanocomposites compatibilized by: a EPDM-g-MAH and b ENR50 with
compatibilizer to clay ratio of 1, 2 and 3 [147]
Fig. 12 Stress–strain curves of a KH570-Al
/NR Nanocomposites with different filler content
[103] b NBR and its composites [148]
86 D. Ponnamma et al.
strength increases by 24 and 42 % respectively for 5 and 10 phr of NCC filler
loading, which is equivalent to that attained with two times of commercially pre-
cipitated CaCO
. The synergistic effect of fumed silica and POSS nanofillers on the
mechanical properties of RTV silicone rubbers are reported [145] as shown in
Fig. 13. The tensile strength of the neat elastomer increases from 0.48 to 1.10 MPa
with the amount of filler loading (Fig. 13a), whereas the elongation at break increase
from 58.6 to 164.1 % in the beginning and thereafter decreases with fumed silica
(Fig. 13b). Both POSS-rich domains and fumed silica phases significantly enhance
the thermal and mechanical properties of RTV silicone rubbers. The tensile prop-
erties of NBR/PAni DBSA blends containing 15 and 27 % of PAni are compared
[150] and good conclusions were drawn. Even though PAni. DBSA exhibit poor
mechanical strength, the presence of 15 and 27 % of it in blends of NBR fabricated
by physical mixing and in situ polymerization resulted in an increase of both tensile
strength and elongation at break values compared to pure NBR.
The dynamic mechanical property analysis reveals the storage modulus (E
) and
loss factor (tan d) of composites. These values for NBR/CB and NBR/EG/CB
composites as a function of temperature are shown in Fig. 14. The E
values for
NBR/EG/CB nanocomposites are observed to be higher than that of NBR/CB and
NBR/EG/CB microcomposites, similar to the tensile observation. For nanocom-
posites, the energy dissipation behavior is particular, for instance the hysterisis loss
peak first decreases, broadens, and then increases, indicating the enhanced filler
volume fraction and good nano-size dispersed graphite—rubber interfacial inter-
action [151]. This clearly illustrates that all nano particles have the unique ability
of giving a positive effect on the mechanical strength in their composites, which
again increases with the filler concentration and nature of dispersion. Similar trend
has been observed in the case of natural rubber carbon nanotube composites as
well [152].
Fig. 13 Effects of the
relative loading amount of
fumed silica on mechanical
properties of the novel RTV
silicone rubbers: a tensile
strength b elongation at break
Rubber Nanocomposites: Latest Trends and Concepts 87
3.2.2 Rheological Properties
Generally fillers are added into rubber to influence its physical properties. The
effectiveness of a composite depends on the physical and chemical nature of the
filler, which in turn depends on the amount of filler, filler–rubber and/or filler–filler
interactions. This includes the nature and morphology of the filler, surface
chemistry, concentration and the rate of dispersion in the matrices. Rheology is a
very significant tool to explain the viscoelastic behavior of the material based on
the nature of filler particles incorporated in the nanocomposites and understanding
of the rheology of filled elastomers is significant in the design, processability and
development of nanocomposites. This technique not only determines the final
products properties but also controls the fluid and heat transfer characteristics
during the processing. Thus it is very important to examine the dynamic viscosity
as well as moduli based on the filler loading as well as the experimental factors
like temperature, frequency, and strain rate [153]. Fillers in viscoelastic polymers
can reduce melt elasticity and hence influence phenomena such as die swell [154].
At high filler loading yield stress is observed in composite systems, which is
associated with particle interactions within the matrix. At this point, viscosity of
the material enhances highly, showing a solid like behaviour. The difficulties
addressed for rheological measurement of composites include the significantly
smaller dimensions of suspended particles than the characteristic dimensions of the
measuring equipment and the wall effect (formation of a melt layer at the wall
surface) caused by a nonhomogeneous distribution of the dispersed phase. This
layer of relatively low viscosity existing at the melt boundary gives rise to
lubrication effects or apparent wall slippage [155]. Additionally, inertial and
gravitational effects should be negligible.
The variation in storage modulus (G
) with frequency for different NR and SBR
blend nanocomposites is shown in Fig. 15. Higher complex viscosity and storage
modulus is observed for SBR when compared to NR, particularly at low frequency
region. But the clay platelets have more influence in increasing these parameters
for NR than that of SBR, suggesting greater ability of NR for intercalation process.
Fig. 14 Storage modulus and loss factor of NBR/CB and NBR/EG/CB composites [148]
88 D. Ponnamma et al.
On considering the polarity of the phases, the filler is expected to be present in
both NR and SBR non polar constituents. The more intercalation effect of nano-
clay on NR than SBR is also evidenced from the melt viscoelastic behavior of NR/
SBR/clay composite (Fig. 15).
One of the important experimental parameters in determining the reinforcing
action of elastomer properties is Payne Effect. It is known that the dynamic
performance of tyres such as resistance to friction depend on the nonlinear vis-
coelastic behavior of tyre material, which is a vulcanized rubber composite. This
kind of studies is very important as far as the fuel consumption and safety is
considered and a lot of studies are focusing on the Payne effect. The effect is
defined as the variation of storage modulus with strain amplitude and is related to
the filler/rubber molecular interactions. Obviously the filled matrix shows higher
storage (G
) and loss modulus (G
) values than neat rubber in the rubbery region
depending on the filler dimensions.
Figure 16 illustrates respectively the loss and storage (G
and G
modulus, at small and large strain amplitudes. The Payne effect is generally
demonstrated through the analysis of the low strain dynamic mechanical properties
which describe the viscoelastic response of the rubbery material to periodic
deformation. Filled elastomers display a unique dynamic viscoelastic behavior
characterised by an amplitude dependence of the dynamic and loss moduli. The
difference between the two limits (G
) has been shown to depend on several
parameters. It increases with increasing concentration of filler and with the specific
surface area of the particles while it decreases with increasing temperatures and
with improved dispersion. The contributions of the filler to the mechanical
behavior are strongly strain dependent. Considering the influence of rubber
occlusion by the filler particles, hydrodynamic effects account very well for the
rheology of filled rubber at moderate strain levels [157160]. At higher strains,
debonding of the polymer chains from the filler, orientation of the latter phase, and
microscopic crack deviation have been involved to explain the various physical
Fig. 15 Melt shear storage
modulus (G
) as a function of
frequency for unfilled NR,
SBR, simple blend of NR/
SBR, and filled counterparts
Rubber Nanocomposites: Latest Trends and Concepts 89
The magneto-rheological properties of nitrile rubber reinforced irregular,
micrometer iron particles are examined within the frequency range 100–1250 Hz
applying an external magnetic field. This material has good application in vibra-
tion isolators [161]. The shear modulus of this composite depends strongly on both
frequency and magnetic field, while the loss factor is almost independent of those
factors. In this technique, the instrumental set up increases the magnetic induction
on one side while reducing the magnetic cross transfer via another part. The
magnetic field independent loss factor and the frequency independent relative
shear modulus magnitude of the material have important implications such as
statistical elastic and quasi—statistical shear modulus modelling and frequency
split. Of these, one factor considers magnetic field dependent, elastic and static
properties while the other factor the frequency dependent, viscoelastic rubber
properties within the audible frequency range.
The storage modulus (G
) as a function of frequency for a blend/CNT nano-
composite is shown in Fig. 17 with filler loading from 1 to 20 wt%. As expected,
the influence of the nanofillers is more pronounced in the low-frequency region
where G
increases at a fixed frequency, and the slope decreases and tends rapidly
Fig. 16 Schematic
representation of the strain
dependence of the dynamic
moduli for filled vulcanizates
Fig. 17 Storage modulus
) as a function of
frequency at T 120 °C for
different blend/CNT
composites [162]
90 D. Ponnamma et al.
to zero when the filler content increases. This phenomenon appears from 1 wt% of
CNT and could be explained by the existence of a percolated network. Above this
percolation threshold, G
was independent of the frequency, which is characteristic
of a viscoelastic solid. Many studies report this phenomenon [163165].
3.2.3 Electrical Properties
Conducting nanoparticles are added to various elastomer matrices to impart con-
ductivity and this paves the way to flexible electronics. Fillers like CNTs, graphene
and other graphitic fillers have the ability to reduce the volume resistivity to a great
extent; the values for various nanocomposites are represented in Table 4.
The variation of volume resistivity with the nanotube content is given in
Fig. 18. The percolation threshold for the three elastomer matrices, NR, SBR and
EPDM is found to be 0.5 phr (volume fraction = 0.002), which is much lower than
the already reported values [161, 167] for these elastomers as well as composites
containing conventional microscale conducting fillers [168]. This property of
CNTs to form a conducting network at low level of filler loading is due to their
intrinsically high conductivity and high aspect ratio. The improvement in electrical
conductivity obtained here indicates better dispersion of CNTs because of the
processing method (sonication) evidenced from the microscopic technique.
When the carbon black and PAni fillers dispersed in a given polymer matrix are
considered, the carbon black containing systems offer no solubility effects, and
structuring of carbon black particles occurs during the melt processing step. But in
the doped PAni polymer systems the shorter chains may partially dissolve in the melt
and upon cooling partially precipitate out to form fine, discretely dispersed, doped
PAni particles resulting in a conducting network. This phenomenon explains the
conductivity increase with PAni-DBSA loading (Fig. 19). EPDM/PAni-DBSA-R
crosslinked by electron beam irradiation produces highly conductive materials.
Additional electron beam irradiation also enhances the conductivity.
Figure 20a shows the variation of log DC electrical conductivity of the com-
posites against loading. Conductivity of pure XNBR in the order of 10
with CNT loading and becomes 10
orders of magnitude. At low filler concen-
tration the conductivity remains very close to that of the pure, electrically
Table 4 Electrical conductivity of elastomer/conductive fillers nanocomposites
Elastomer Concentration of filler Electrical conductivity
NR [108] 3:40 phr
3.2 9 10
EPDM [108] 3:40 phr
2.1 9 10
XNBR [134] 3.9 phr MWCNT 0.07 (S/cm)
NBR [150] PAni 48 wt% 2 9 10
SBR [166] Graphene 5 % 4.56 9 10
Rubber Nanocomposites: Latest Trends and Concepts 91
insulating polymer matrix, since the fillers occur only individually or in small
clusters throughout the matrix [170]. Percolation threshold and drastic increase in
electric conductivity is a result of continuous network of CNT in the polymer
matrix. The conducting CNTs are either making physical contact between them or
are separated by small gaps [171].
The same effect of decrease in volume resistivity of silicone rubber with the
increase of filler content is represented in Fig. 21. The percolation threshold for
graphene is about 2 wt% with volume resistivity of 10
X cm whereas for MWNTs
it is about 5 wt% with volume resistivity of 4.21 9 10
X cm. The two dimen-
sional planar structure of graphene facilitates its better dispersion in the matrix
compared to MWNTs. NTs tend to aggregate in silicone rubber, giving rise to a
larger percolation value.
Fig. 18 Dependence of
volume resistivity on CNT
loading for NR, SBR, and
EPDM composites [169]
Fig. 19 Conductivity for
crosslinked with resin (square
shaped) and electron beam
using (circle shaped) 75 kGy
and (triangle shape) 150 kGy
92 D. Ponnamma et al.
When both graphene and carbon nanotubes are filled in silicone rubber com-
posites, carbon nanotube get well dispersed in presence of graphene and good
conductive network is formed. Carbon nanotubes act as conductive bridges
between graphene layers and the matrix. The synergistic effect of carbon black,
carbon nanotube and graphene in forming the conductive network is schematically
represented in the Fig. 22a, where as Fig. 22b shows the same effect between only
CNTs and graphene flakes.
The large surface area of graphene and high aspect ratio of carbon nanotubes
contribute towards the synergistic effect. These one dimensional and two dimen-
sional fillers together form a ‘conductive bridge’ in the silicone rubber (Fig. 22).
MWNTs are difficult to disperse in SR alone, whereas it is much easier with the aid
of graphene. The strong interaction between graphene and SR as well as between
graphene and MWNTs account for the good dispersion of NTs. Graphene behaves
as a compatibilizer in this case. Both physical isolation and hydrogen bonding
between graphene and MWNTs during the dispersion lead to the better dispersion
of NTs.
Fig. 20 Variation of log DC conductivity (a) and AC conductivity at different frequencies
(b) against concentration [118]
Fig. 21 The resistivity of
silicone rubber composites
Rubber Nanocomposites: Latest Trends and Concepts 93
3.2.4 Permeability
Gas barrier properties of nanocomposites is related to the transmission of penetrant
molecules through the composite membranes and are very important in the
packaging industries, gas separation, solvent studies etc. This phenomenon
depends not only on the nature of polymer and diffusant but also varies with the
density and crystallinity of the polymer, filler orientation, crosslinking, plasticiz-
ers, humidity and method of preparation of the composite. The density, crystal-
linity, orientation and crosslinking have a negative effect on permeability, the
higher these values, the lower will be the gas permeability. Thickness of the film
does not affect the permeability much, though different values are obtained from
films of variable thickness. Inorganic fillers decrease permeability based on the
type, shape and amount of filler and its interaction with polymer. Humidity and
presence of plasticizers increases permittivity, being the effect more pronounced
for hydrophilic polymers in the former case. Specific mechanisms by which dif-
fusion occurs in polymeric systems have been reported [173]. Permeation does not
depend on pressure, whereas an increase in temperature leads to decrease in
penetrant solubility.
Nanoparticles having plate like structure have the unique ability to enhance the
barrier properties of polymer films due to the formation of tortuous path [174] and
by reduction of polymer mobilities. These interact with the elastomers, reduces its
free volume and act as impermeable obstacles to gas molecules. It is important to
develop barrier properties of rubber nanocomposites with superior mechanical and
dynamic mechanical properties. The need for packaging and adhesive applications
paves way for the scope of technological developments in this area. Recently a lot
of scientists have done studies on gas transport in various elastomer nanocom-
posites. Kojima et al. [175] synthesized nitrile rubber/clay hybrid with 70 % of the
permeability of neat NBR. Gatos et al. [176] have investigated the effect of the
Fig. 22 a Microstructural developments in nanofiber based nanocomposites in the presence of
CB [172] b Schematic of the synergistic interaction between graphene and carbon nanotubes
94 D. Ponnamma et al.
aspect ratio of silicate platelets on barrier properties of hydrogenated acrylonitrile
butadiene rubber (HNBR)/layered silicate nanocomposites and found good cor-
relation with Nielsen’s model. Similar studies with clay [177179] and graphite
[180] were also reported on acrylonitrile butadiene rubber (NBR). Natural rubber
latex based nanocomposites with an aqueous dispersion of layered clay have also
reported for their high barrier properties [181]. Influence of processing conditions
in regulating the transport properties of polyurethane/clay nanocomposites has
established by Herrera-Alonso et al. [182]. Meneghetti et al. have reported styrene-
butadiene rubber-clay nanocomposites with enhanced mechanical and gas barrier
properties [183]. They found that surfactant chain length and functional groups
determine the extent of dispersion and the modified nanoclays exhibit the best
results. Generally the presence of platelet-like silicate layers greatly reduces the
permeability for most of the elastomers due to their impermeability to diffusing
molecules [184]. This enhances the path length required for the diffusant to travel
through the composite [185]. The permeability values for various nanocomposites
are given in Table 5.
Figure 23a, b illustrate the oxygen transmission rate (OTR) values of cloisite
15A/NR nanocomposites at different loadings of cloisite 15A respectively at 45 °C
and at various temperatures. The enhancement in barrier properties for the com-
posites over NR has been shown by plotting the relative permeabilities of these
nanocomposites at same temperatures. It was observed that both response time and
time to equilibration decreased with increase in temperature, which is explained in
terms of increased membrane mobility and easier adsorption of permeants onto the
As described above, increasing in filler loading can provide longer diffusion
path, thus improving the gas barrier property. Lu and Mai [190] and Bharadwaj
[191] and Nielson models are generally used to explain the permeability effect
based on the filler aspect ratio (diameter/thickness for silicate layer). Since
exfoliated clay layers have much larger aspect ratios than intercalated structures,
they have better gas barrier property. The dependence of relative gas permeability
on the inorganic filler volume fraction of epichlorohydrin with predictions based
on simple Nielsen model for different aspect ratios is showed in Fig. 24. The
Table 5 Gas permeability of rubber nanocomposites
Elastomer Filler Content Processing Permeant Relative reduction
NR [186] TRG 1.7 (vol%) Solution
Air 60
IIR [136] Clay 8 (vol%) Solution Oxygen 20
rubber (ECO) [187]
Clay 40 % Melt Nitrogen 70
SR [188] FGS 0.43 (vol%) Nitrogen 7.3
1.31 (vol%) Nitrogen 49
EPDM [187] Clay 40 % Melt Nitrogen 30
SBR [187] Clay 40 % Melt Nitrogen 50
Rubber Nanocomposites: Latest Trends and Concepts 95
experimental values are in good correlation with the theoretical predictions at
lower filler loadings for fillers having aspect ratio 50 and at higher loading for the
fillers with aspect ratio 75.
3.2.5 Morphology
Morphological analysis has very significance as far as the nanocomposite prop-
erties are considered. Morphology is an essential tool for the characterisation of
the filler dispersion inside the polymer matrix and also the nature and type of
interfaces. Figure 25 illustrates the transmission electron micrographs of the cal-
cium carbonate reinforced composites of nitrile rubber. Lower filler loading
Fig. 23 OTR values of a clay/NR nanocomposites at different loadings of cloisite 15A at 45 °C
and b of 6 phr clay filled NR nanocomposites at different temperatures [189]
Fig. 24 Relationship
between relative gas
permeability (Pc/Pp) of
ECOCNs (epichlorohydrin)
and inorganic volume
fraction. The dotted curves
are numerical predictions for
disk-shaped inclusions with
aspect ratios 20, 50, 75, 100
according to Nielson model
96 D. Ponnamma et al.
essentially gives the idea of filler dispersion whereas at higher loadings the
nanoparticles tend to have an agglomerating tendency which is inappropriate
during the composite manufacture.
Morphology is really helpful for the characterization of carbon nanotube
reinforced composites since the nanotubes have very strong tendency to form
bundles due to their polar nature. Apart from the level of dispersion, the nature of
interfacial interaction and the type of bonding in composites can also be found out
from the micrographs. This is clear from Fig. 26, where three different kinds of
nanocomposites are studied. Figure 26a–c shows typical TEM images of produced
MWNT1s in rubber matrix containing 5, 9, and 16 wt% filler. MWNT2-filled
rubber nanocomposites (Fig. 26d–f) depict the tortuous configurations of MWNTs
after milling and their homogeneous dispersion in the composites. To further
investigate the 3D morphology, the configurations of the MWNT2-filled rubber
composite have also been investigated using 3D images with detailed information,
as shown in Fig. 26g–i.
Fig. 25 TEM micrographs of NBR–nanocalcium carbonate composites a 0 phr, b 2 phr, c 5 phr,
and d 10 phr [192]
Rubber Nanocomposites: Latest Trends and Concepts 97
The modification of nanotubes and hence the enhanced filler dispersion is also
evidenced by using TEM [187]. The high resolution transmission electron
microscopy image of natural rubber composite of expanded graphite and carbon
black is also reported [186]. The synergistic effect of two fillers in terms of good
filler–filler and filler-polymer interactions can be well explained by analyzing the
TEM image. The dispersion of reduced graphene oxide (RG-O) into natural rubber
(NR) was also observed from morphology and is correlated with the dramatic
enhancement in the mechanical, electrical, and thermal properties of composites
[185]. Co-coagulating a stable RG-O suspension with NR latex afforded a web like
morphology consisting of platelet networks between the latex particles, while two-
roll mill processing broke down this structure, yielding a homogeneous and
improved dispersion. The physical properties of composites with both morphol-
ogies were compared and found that the network morphology was highly bene-
ficial for thermal and electrical conductivity properties and greatly increased
Fig. 26 TEM images of the produced composites containing 5, 9, and 16 wt% of fillers. a–c
MWNT1s/rubber, df MWNT2s/rubber, gi corresponding 3D images of MWNT2s/rubber. The
thickness of each sample is 130 nm [192]
98 D. Ponnamma et al.
stiffness but was detrimental to elongation. In addition to the microscopic tech-
niques such as TEM, SEM and AFM, other techniques like XRD, Raman etc. are
also used to characterise the nature of filler and composite morphology. Figure 27
illustrates the X-ray diffractogram of various composites of clay and graphitic
fillers. The intensity and shift in the 2h values gives clear picture about the filler
exfoliation [193]. In the CNT and graphene case Raman spectroscopy plays an
essential role for the structural information.
The importance of bio fillers in fabricating nanocomposites is increasing to a
wider extent nowadays. Bio nanocomposites are composite materials comprising
one or more phase(s) derived from a biological origin and the size is of nano range.
Polysaccharides such as starch and cellulose have been used as reinforcing agents in
many polymer matrix like natural rubber. The various advantages like renewability,
non-toxicity and biocompatibility, of the bionanocomposites prepared from
nanofillers like cellulose fibers, chitin whiskers, and starch nanocrystals are made
use in a wide range of applications, like medicines, coatings, food products and
packaging. Both solution blending and dry mixing methods have been employed for
the development of bionanocomposites and they offer potential eco-friendly sub-
stitutes for the conventional filler carbon black [88]. It is found that the cellulose
nanowhiskers prepared from bio sources are good reinforcement for natural rubber
system [194]. Figure 28 explains the random orientation of nanowhiskers in the NR
matrix and their homogeneous distribution. SEM also points out the dispersion of
fillers without microscale aggregation, especially at 5 wt% CNW concentration.
Morphology is again used in finding out the nature of distribution of starch
nanocrystals in rubber medium by Bouthegourd et al. [195]. The AFM images
shown in Fig. 29 illustrates the uniform distribution of the nanocrystals at low
filler content (\15 %), while a tendency for agglomeration is observed for content
greater than 15 % w/w. The nanocrystals were prepared from potato base medium
Fig. 27 XRD profiles of a graphene, silicone rubber and silicone rubber/graphene composite
[124] and b EG, modified EG and EG/MEG filled NR based nanocomposites in presence and
absence of CB [186]
Rubber Nanocomposites: Latest Trends and Concepts 99
by following the method of hydrolysis. The electrical resistance value determined
from the dielectric studies also supports the uniform distribution of crystals
throughout the matrix. The increase of the electrical resistance at 15 wt% indicates
that nanoparticles act as a barrier to the electrical charge movements.
All the above discussed properties give a detailed explanation of the
improvement in composite properties while filling the matrix with nano particles.
3.2.6 Applications
A lot of applications have been envisaged for the nanocomposites developed. The
synthesized composite membranes can be sandwiched between two electrodes to
produce membrane electrode assembly (MEA) using hot press method at constant
conditions of temperature, pressure and time. The performance of the fabricated
Fig. 28 SEM images of NR/Cellulose nanowhiskers nanocomposites: a neat NR, b NR-
CNW2.5, c NR-CNW10 [194]
Fig. 29 Effect of starch potato nanocrystal composition on the volume and surface electrical
resistivity of the nanocomposites. In this figure the AFM images for 5, 15 and 20 % of starch are
also displayed. Lines are drawn as a guide for the eyes [195]
100 D. Ponnamma et al.
MEA was tested in a single PEM fuel cell using hydrogen as the fuel gas and
oxygen as oxidant at room temperature [109]. Synthesis and characterization of
nanosilver based antimicrobial natural rubber latex foam can strongly inhibit the
growth of bacteria and fungus [132]. Elastomer nanocomposite with high elec-
tromagnetic dissipation and shielding properties is useful in electromagnetic
interference (EMI) shielding devices. Combining the good electrical properties,
flexibility and fluid resistance, nanocomposites yield very versatile and light
weight materials for a variety of electromagnetic static discharge and EMI
applications [196]. Porous nano composite materials have numerous applications
in areas such as catalysis, chromatography, and separation, where control over
pore structure and pore size strongly influences the efficiency of the material.
POSS is noted for fabricating such composite materials [197]. Two dimensional
fillers impart superior barrier properties to the composite membranes. Several
nanocomposites of graphene and carbon nanotubes are reported as good dielectric
materials. In addition to composites formed from single filler, multiple fillers also
contributes towards better application due to their synergistic effect.
4 Conclusion
A brief account of the recent researches on the synthesis, properties and appli-
cations of rubber nanocomposites has been done. Various nano fillers like layered
silicates, carbon nanotubes, graphene, POSS, PAni, nanosilica, biofillers, graphene
oxide etc. were addressed. It is found that conductive nanofillers like CNT and
graphene have tremendous applications in electric and dielectric fields as they can
impart conductivity to the rubber insulator. The barrier properties of rubbers have
superior applications in tyre industry and fillers with two dimensional plate like
morphology are useful in this case. The incorporation of nano-fillers into tyre
components is driven by potentially higher overall performance, especially
focused on fuel efficiency through reduced weight and energy dissipation. Because
of the enhanced surface area and high aspect ratio all kinds of nano fillers can
result in superior mechanical strength. Though the nanocomposites offer vast
applications, more studies should be focused on it to completely exploit their
properties. Dispersion, modification of fillers, improved interfacial interactions are
some of the problems yet to be addressed. Effort has been made to explain the
important aspects of this area emphasizing the challenges. Further researches and
more enhancement in properties and superior applications are anticipated.
Acknowledgments The authors would like to acknowledge the University Grants Commission
and the Department of Atomic Energy Consortium for giving enough funding to carry out the
research works on Carbon nanotube. Thanks are also due to Nanomission of DST, New Delhi for
their support. We also acknowledge the financial support from the Ministry of Higher Education,
Science and Technology of the Republic of Slovenia through the contract No. 3211-10-000057
(Center of Excellence Polymer Materials and Technologies).
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Rubber Nanocomposites: Latest Trends and Concepts 107
... NBR is used in environments with temperature ranges of ~ -25°C to 120°C, though; the rubber life is shortened when the temperature exceeds 100 °C. On other hand, the elastomeric characteristics of this rubber elasticity are provided by vulcanization and the formation of compounds with several fillers [1][2][3]. The vulcanization process converts rubber into a more durable material, in which one of the additives "Sulfur" is forms cross-links between the rubber molecular chains and results in increasing rigidity. ...
... Since fem at the equilibrium state, the chemical potential of the solvent in the polymer will be equal to the pure solvent. Therefore, equation (1) is equal to equation (2). Also, after rearrangement, the final expression for finding the crosslink density (D) is given according to the standard of the swelling test. ...
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Abstract. Nanocomposites elastomers are being developed in the field of nanomaterials as it has low weight and high properties compared to the conventional rubbers. Acrylonitrile butadiene rubber (NBR) is used in automobile parts due to its ability to resist oil. In this research, Carbon Black nanoparticles (CBnp) type FEF N550 was used to reinforce this rubber to reduce the swelling ratio. Therefore, physicochemical characteristics were investigated for five different samples of vulcanized CBnp/NBR nanocomposites with 0, 0.2, 0.6, 1.2 and 2.4 phr of CBnp using the solution mixing method. The homogeneity of these nanocomposites was evaluated by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Furthermore, the influence of different contents of CBnp on the tensile strength was analyzed. The results showed that the crosslinking densities in the CBnp/NBR nanocomposites structure have been improved compared with the neat vulcanized NBR and the mechanical properties as well. t’s an essential result which can employ it to prepare washers (rubber rings) resist against oils for several applications. Keywords: Acrylonitrile Butadiene Rubber (NBR); rubber nanocomposites; crosslink density in elastomers.
... In this method, the monomers of the polymer are dispersed in water together with an emulsifying agent and the clays, as can be seen in Fig. 8a). It is beneficial to achieve a good interaction between the rubber matrix and the reinforcement, since there is a joint polymerization between the rubber chains and the clays, leaving a nanocomposite where some of the clay sheets are embedded in the rubber particles, while some polymer chains are adsorbed on the surface of the clay particles [66], due to this, a better dispersion of the reinforcement can be obtained [67]. ...
... Polymerization is promoted with temperature, and the clay swelling process occurs directly in the polymerization medium (water) and in some cases, by the low molecular weight of liquid monomers [67]. One of the drawbacks of this method is that requires a certain time period to form the nanocomposite and depends extensively on the polarity of the monomers, the type and surface of the filler and the initiation temperature of the polymerization reaction [4]. ...
This book presents emerging economical and environmentally friendly polymer composites that are free of the side effects observed in traditional composites. It focuses on eco-friendly composite materials using granulated cork, a by-product of the cork industry; cellulose pulp from the recycling of paper residues; hemp fibers; and a range of other environmentally friendly materials procured from various sources. The book presents the manufacturing methods, properties and characterization techniques of these eco-friendly composites. The respective chapters address classical and recent aspects of eco-friendly polymer composites and their chemistry, along with practical applications in the biomedical, pharmaceutical, automotive and other sectors. Topics addressed include the fundamentals, processing, properties, practicality, drawbacks and advantages of eco-friendly polymer composites. Featuring contributions by experts in the field with a variety of backgrounds and specialties, the book will appeal to researchers and students in the fields of materials science and environmental science. Moreover, it fills the gap between research work in the laboratory and practical applications in related industries
... Одним из перспективных вариантов является введение в структуру полимера таких частиц, как модифицированный кремний, наноалмазы, графеновые пластинки, фуллерены, нанотрубки, глина, бионаполнители и пр. [5][6][7]. ...
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The paper presents results of studying mechanical properties of polymer composites depending on types of filler particles (granular - carbon black, nanodiamonds; layered - graphene plates; fibrous - single-walled nanotubes). These nanofillers differ greatly from each other in their structure and geometry. A significant difference in behavior of nanocomposites was revealed even with little introduction of particles into the elastomer. The highest level of reinforcement of the matrix was obtained when single-wall nanotubes and detonation nanodiamonds were used as fillers. The viscoelastic properties and the Mullins softening effect [1-4] were investigated in experiments performed with material samples subjected to complex uniaxial cyclic deformation. In these experiments, the amplitude of deformations was changed step by step; and at each step a time delay was specified to complete rearrangement processes of the material structure. It was found that a pronounced softening effect after the first cycle of deformation and significant hysteresis losses occur in the material filled with single-walled nanotubes. These characteristics are insignificant for the rest of nanocomposites until elongation increases twofold. In accordance with the obtained results, a new version of the mathematical model to describe properties of the viscoelastic polymer materials was proposed. The constants of the constitutive relations were calculated for each material; the theoretical and experimental load curves were compared. As a result, the introduced model is able to describe the behavior of elastomeric nanocomposites with a high accuracy. Moreover, this model is relatively easy to use, suitable for a wide range of strain rates and stretch ratios and does not require the entire history of deformation as needed for integral models of viscoelasticity.
... According to Ponnamma [50], mechanical performance of elastomer nanocomposites depends on several factors such as the filler dispersion, the degree of interfacial adhesion between the elastomers and the filler, as well as the crosslink density of the composite. For the analysis of mechanical strength properties (tear resistance, cutting resistance and tensile strength) of XNBR composites with the content of both types of nanofillers, structural studies can be helpful. ...
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The objective of the work was to investigate the possibility of simultaneous application of different type of nanofillers: graphene oxide with carboxylic groups and modified bentonite nanoparticles to carboxylated acrylonitrile-butadiene rubber (XNBR) and to determine the effect on the structure, mechanical and barrier properties of the composites. The composites were designed for use in protective clothing and gloves. Rubber compounds were crosslinked by a hybrid set with simultaneous use of sulphur (1.5 phr) and magnesium oxide (2.5 phr). Graphene oxide and bentonite particles were characterized by BET test method. The XNBR composites with nanofillers were studied in terms of structure (WAXS) and types of chemical bonds (FTIR), barrier properties against chemical substances (mineral oil) and swelling properties, as well as mechanical properties (puncture resistance, tear resistance, cut resistance, abrasion resistance, tensile strength). Simultaneous incorporation to XNBR of two types of nanofillers, bentonite in the amount of 1.0-4.0 phr, graphene oxide with carboxylic groups in the amount of 1.0-2.0 phr, affected positively the mechanical parameters. The most significant improvement was noted for the parameter specifying the puncture resistance, almost three-fold improvement from 34 ± 2 N for unfilled XNBR composite to 91 ± 5 N for XNBR composite filled with 2 phr of bentonite (XNBR Bent. 2), or one and a half to 56 ± 5 N for XNBR composite filled with 2 phr of bentonite and 2 phr of graphene oxide (XNBR Bent 2 GO 2). The composites showed equally high resistance to penetration of the selected test chemical –mineral oil. The breakthrough time for XNBR composites without the nanofiller and containing differential amounts of nanofillers was very long and similar to that obtained for the reference sample (480 min).
Awareness of the environmental implications of conventional reinforcing fillers and the urge to reduce the carbon footprint have lead researchers to focus more on natural and sustainable materials. Nanocellulose from multitudinous sources finds use in elastomer engineering because of its distinctive properties, such as renewability, sustainability, abundance, biodegradability, high aspect ratio, excellent mechanical properties, and low cost. Green alternatives for conventional fillers in elastomer reinforcing have gained considerable interest to curb the risk of fillers from nonrenewable sources. The differences in properties of nanocellulose and elastomers render attractiveness in the search for synergistic properties resulting from their combination. This review addresses the isolation techniques for nanocellulose and challenges in its incorporation into the elastomer matrix. Surface modifications for solving incompatibility between filler and matrices are discussed. Processing of nanocomposites, various characterization techniques, mechanical behavior, and potential applications of nanocellulose elastomer composites are also discussed in detail.
Silica is a reinforcing filler which is known for its ability to improve wet/snow grip and rolling resistance in tyres. However, incorporating Silica in high quantities impairs other significant features like physical properties and processing behaviour of the compounds. In this study, the focus was on balancing rolling resistance and grip properties while attempting to nullify the negative effects of Silica, by arriving at an optimum ratio of combination of Carbon Black and Silica. Three different compounds were prepared – COMP_1 had CB:Silica in 2:1 ratio, whereas COMP_2 and COMP_3 had CB:Silica in the ratios 1:1 and 1:2 respectively. The impact of their dosage on various properties were investigated. Taking into consideration abrasion loss and grip properties, 1:1 ratio was deemed to possess the optimized ratio.
Many researchers have been trying to improve rubber composites because they are commonly used in a wide range of applications. Incorporation of nano-fillers in a rubber matrix is the most acceptable way to improve the mechanical and electrical properties of rubber composites. A nanometer-sized filler, such as K0.15Cr0.02Ni0.83O (KCNO), has rarely been used to improve the properties of rubber composites. Epoxidized natural rubber (ENR) was chosen for blending with KCNO nanoparticles based on its polarity and chemical resistance. The aim of this work is to investigate the effects of filler loading (0.5, 1.5, and 5 phr) on the curing characteristics, dynamic mechanical, mechanical, morphological, and dielectric properties of rubber composites. From the results, rubber vulcanizates with 1.5 phr of KCNO as filler exhibit better tensile strength and 500% modulus compared to other ENR specimens containing KCNO. ENR containing 1.5 phr of KCNO also has a higher storage modulus (E′) and glass transition temperature (Tg). The results of a microstructural characterization on a sample containing 1.5 phr of KCNO show that the natural rubber matrix and KCNO are effectively dispersed, indicating that the rubber and KCNO are likely well-matched, therefore curing simultaneously and forming a continuous phase. Furthermore, ENR containing 1.5 phr of KCNO has a greater dielectric constant (12.87 at 5 kHz) than other samples.
The numerous combinations of different rubbers as matrix materials with graphene/graphene derivatives as nanofillers, which are used to fabricate graphene/rubber nanocomposites, are illustrated in this study. The different processing methods for producing graphene/rubber nanocomposites are investigated in depth. Furthermore, based on the results of various experiments performed with the produced graphene/rubber nanocomposites, an attempt is made to establish an outline over the influence of graphene nanofillers inside the rubber matrix. To explain the composite material characteristics, different processes, and the consequence of the incorporation of graphene/graphene derivatives nanofillers, a unique approximation has been accomplished.
The present work aims to investigate the effect of hybrid nanofillers in bromobutyl rubber/epoxidized natural rubber (ENR 50) composites for developing highly air‐impermeable nanocomposites. The nanocomposites with hybrid nanofillers were prepared by a simple melt mixing method, and the morphology of the developed nanocomposites was studied using X‐Ray diffraction, transmission electron microscopy, and atomic force microscopy. Improvement in the mechanical, barrier and dynamic properties can be observed for hybrid nanocomposites compared to the composites filled with individual graphene nanoplatelets (GNPs). The strong interfacial attraction between GNP monolayers enhance its aggregation in nanocomposites. While, in the current study the results are showing that the addition of graphene oxide, nanoclay, and nanosilica enhances the dispersion of GNP in the composites. The homogeneous dispersion of GNP nanofillers will develop a tortuous pathway in the composites, which are responsible for their air barrier properties. Bound rubber content and dynamic strain measurements (Payne effect) show a maximum value for binary nanocomposites.
The hemihydrate calcium sulfate whisker (HCSW) was modified by γ‐(methacryloxy)propyl trimethoxy silane (KH570) and trimethylolpropane tris(3‐mercaptopropionate) via wet modification and thiol‐ene click reaction, and then the unmodified and modified HCSW were added into α, ω‐dihydroxy polysiloxane (DPS) matrix to prepare silicon rubber composites. After the dual‐surface modification, the surface of HCSW was transformed to hydrophobic, the hydration of whisker was obviously improved, and the whisker dispersed more evenly in the polymer. The mechanical properties, dynamic mechanical properties, and the medium resistance of the silicone rubber composite were compared. The tensile test shows that the silicone rubber shows better mechanical properties after adding the modified whiskers, among which HCSW‐KH570‐SH has the most significant reinforcement effect. Moreover, DPS/HCSW‐KH570‐SH shows the best medium resistance in toluene, gasoline, and water. The addition of modified whiskers can improve the storage modulus of silicone rubber significantly, while DMA and DSC show that the addition of modified whiskers can reduce the glass transition temperature of silicone rubber. The bound rubber indicates that the interface interaction between HCSW‐KH570‐SH and silicone rubber is the best. A new organic–inorganic hybrid material is synthesized. Surface modification of HCSW is carried out by wet modification and thiol‐ene click reaction, and the double‐surface modified HCSW is used as reinforcing material for DPS materials. The mechanical properties of DPS composites are significantly improved after adding HCSW.
Several new advancements made in the field of tire manufacturing technology and future trends are discussed. Two of the significant factors that have influenced the development new tire manufacturing technologies, include, increasing requirements of automobile manufacturers and growing customer expectations. It is expected that tire manufacturing technology will continue to develop, to accommodate new applications, safety, health and environmental issues, advantages of new materials, such as nano composites, plasma surface modified carbon black, and the development of computer simulation techniques. New polymers and elastomer materials are being developed for tires, to overcome the problems of shortage of natural rubber. New reinforced filler technology is being also being developed, to produce new material for tires. Some of these developments, include the introduction and usage of improved grades of silica and the development of dual fillers and nanotechnology for new tires.
Literature- based survey of investigations related to measurement and evaluation of variation of dynamic properties of carbon black- reinforced rubber with strain. Dynamic test apparatus and its operation techniques are described. Effects of temperature, frequency and of special processing or compounding as well as of vulcanization degree on dynamic shear modulus are discussed. Practical aspects of filler agglomeration effects are outlined, with attention to heat build- up in tires. Normalization of moduli and application of domain model.
Nanocrystalline cellulose was modified by 3-aminopropyl-triethoxysilane (KH550). The modified nanocrys- talline cellulose (MNCC) was further investigated to partially replace silica in natural rubber (NR) composites via coagula- tion. NR/MNCC/silica and NR/nanocrystalline cellulose (NCC)/silica nanocomposites were prepared. Through the com- parison of vulcanization characteristics, processing properties of compounds and mechanical properties, compression fatigue properties, dynamic mechanical performance of NR/MNCC/silica and NR/NCC/silica nanocomposites, MNCC was proved to be more efficient than NCC. MNCC could activate the vulcanization process, suppress Payne effect, increase 300% modulus, tear strength and hardness, and reduce the heat build-up and compression set. Moreover, fine MNCC dis- persion and strong interfacial interaction were achieved in NR/MNCC/silica nanocomposites. The observed reinforcement effects were evaluated based on the results of apparent crosslinking density (Vr), thermo-gravimetric (TG) and scanning electron microscopic (SEM) analyses of NR/MNCC/silica in comparison with NR/NCC/silica nanocomposites.
Silica is widely used in passenger tire treads to improve the balance between wet traction and rolling resistance, compared to the balance achieved when the filler is strictly carbon black. Improvement in wet traction with silica is attributed to the difference in energy loss encountered at high frequencies. The energy loss difference is deduced from the difference in shift factors, determined by time temperature superposition in viscoelastic testing of silica compounds compared to carbon black compounds. Further investigation indicated that some mineral fillers other than silica showed similar behavior. Thus, some mineral fillers could improve tire wet traction without adverse effects on other tire performance traits.