ethylene/vinyl acetate copolymer/clay nanocomposites
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HIGHLIGHT
Ethylene/Vinyl Acetate Copolymer/Clay Nanocomposites
S. K. SRIVASTAVA, M. PRAMANIK, H. ACHARYADepartment of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
Received 21 June 2005; revised 12 September 2005; accepted 10 October 2005DOI: 10.1002/polb.20702Published online in Wiley InterScience (www.interscience.wiley.com).
Suneel Kumar Srivastava was born in 1954 in Ismilepur (Sitapur), Uttar Pradesh. He
received his M.Sc. degree in Inorganic Chemistry from Lucknow University, Lucknow.
Subsequently, he completed his post graduate diploma in ‘‘High pressure technology and
technical gas reactions’’ and Ph.D. under late Professor B.N. Avasthi in the field of ‘‘Solid
state chemistry’’ from Indian Institute of Technology, Kharagpur in 1979 and 1986,
respectively. He also carried out his post-doctoral work in Germany at the University of
Karlsruhe in 1988–89 and 2002, at University of Siegen in 1994 and 1999 as aDAADFel-
low, and at theUniversity of Nantes, France in 2003. He is currently anAssociate Professor
in the Department of Chemistry, Indian Institute of Technology, Kharagpur. His research
interests are in the field of layered materials specially clay and thermoplastic elastomer,
elastomer, plastic, polymer blends and solid polymer electrolyte based nanocomposites:
structure-property relationships. His research field also includes growth of transition metal
dichalcogenides, ternary and quaternary chalcogenides in micro and nanocrystalline forms.
Correspondence to: S. K. Srivastava (E-mail: sunit@chem.iitkgp.ernet.in)
ABSTRACT: This article high-
lights the history, synthetic routes,
material properties, and scope of
ethylene/vinyl acetate copolymer
(EVA)/clay nanocomposites. These
nanocomposites of EVAs are ac-
hieved with either unmodified or or-
ganomodified layered silicates with
different methods. The structures
of the resulting polymer/inorganic
nanocomposites have been char-
acterized with X-ray diffraction,
scanning electron microscopy, and
transmission electron microscopy.
The addition of a small amount of
clay, typically less than 8 wt %, to
the polymer matrix unusually pro-
motes the material properties, such
as the mechanical, thermal, and
swelling properties, and increases
the flame retardancy of these hy-
brids. VVC 2005 Wiley Periodicals, Inc.
J Polym Sci Part B: Polym Phys 44: 471–
480, 2006
Keywords: ethylene/vinyl ace-
tate copolymer (EVA); montmor-
illonite; nanocomposites; scanning
electron microscopy (SEM); swel-
ling; TEM
Journal of Polymer Science: Part B: Polymer Physics, Vol. 44, 471–480 (2006)VVC 2005 Wiley Periodicals, Inc.
SUNEEL KUMARSRIVASTAVA
471
INTRODUCTION
Polymer/layered silicate nanocomposites, known since
the 1990s, are two-phase materials with unexpectedly
improved properties normally unavailable with conven-
tional composites or pure polymers.1–5 Because of this,
the development of these nanocomposites has really
turned the research of advanced materials to a new direc-
tion with a special interest. First, a polymer/clay nano-
composite6 obtained from nylon-6/montmorillonite
(MMT) was reported by a Toyota group of researchers;
clay loadings on a very small scale resulted in thermally
and mechanically high-performance nylon-6. Second,
such a nanocomposite was synthesized by Giannelis
et al.7 through the melt blending of polymers with clays.
Since then, a lot of research work on the development of
high-performance (i.e., industrially applicable) polymer
nanocomposites has been done, and it has exhibited dra-
matically enhanced properties of many matrix materials
as a result of the nanodispersion of silicate layers. These
investigations have led to an interesting point, that sili-
cate layers can be dispersed in a wide range of polymers
on a nanometer level to achieve highly reinforced poly-
mer composites. The extent of the improvement is
directly related to the aspect ratio and the dispersion of
the clay layers in the polymer matrix.8 Depending on the
degree or nature of the dispersion of the clay layers in
the polymer matrix, either intercalated nanocomposites,
in which there is a regular insertion of the polymer
chains between the clay layers, or delaminated nano-
composites, in which the clay layers are randomly and
homogeneously dispersed in the polymer matrix, can be
obtained.9 Because of the structural feature, the latter
type offers the maximum improvement in mechanical
and other physical properties of the polymer. Some-
times, the intercalated and delaminated configurations
coexist.10 Figure 1 displays the different classes of poly-
mer/clay nanocomposites.
Clay minerals are layer-structured materials11–13 and
are formed by the assemblage of tetrahedral and octahe-
dral sheets. These layers are not electrostatically neutral
but rather are negatively charged; this results from the
Monoj Pramanik received his B.Sc.(Hons.) degree in Chemistry from Midnapore
College, Vidyasagar University (V.U.), India in 1996. He received his M.Sc. degree
in Chemistry with specialization in Inorganic Chemistry from V.U. in 1998. Mr. Pra-
manik has received his Ph.D. in Chemistry from the Indian Institute of Technology,
Kharagpur, India in 2005. He has worked on ‘‘Inorganic Layered Materials-Polymer
Nanocomposites’’ with Prof. Suneel Kumar Srivastava, Department of Chemistry,
Indian Institute of Technology, Kharagpur, India. Presently, he is a Postdoctoral
Research Fellow working in ‘‘Coatings’’ in Thames-Rawlins Research Group,
School of Polymers and High Performance Materials, University of Southern Missis-
sippi. He is interested in polymer nanocomposites and coating technology.
Himadri Acharya was born in 1979 at Contai (Midnapore), West Bengal, India.
He received his B.Sc. (2000) and M.Sc. (2002) degree in Chemistry from the
Vidyasagar University, Midnapore, India. Subsequently, he joined the Depart-
ment of Chemistry, Indian Institute of Technology, Kharagpur, for Ph.D. with
Professor Suneel K. Srivastava. His research focuses on nanocomposites sys-
tems with layered inorganic nanomaterials.
Figure 1. Different configurations of polymer/clay nano-
composites.
MONOJ PRAMANIK
HIMADRI ACHARYA
472 J. POLYM. SCI. PART B: POLYM. PHYS.: VOL. 44 (2006)
isomorphous substitution of Al3þ in the octahedral sheet
by Mg2þ and Fe2þ and the substitution of Si4þ in the tet-
rahedral sheet by Al3þ. The negative charge is balanced
by interlayer cations (usually Mg2þ, Naþ, Ca2þ, etc.).Both natural clays and synthetic layered silicates are
being used in the development of polymer/clay nano-
composites and hybrid materials.14,15 Clay minerals used
for the synthesis of polymer nanocomposites are mostly
organomodified. A very limited number of unmodified
clays have been used to develop polymer nanocompo-
sites16,17 because the polymers are to be hydrophilic and
sufficiently polar.18 The organomodification of clay
could change the hydrophilic nature to a hydrophobic
one to create an appropriate environment for the interac-
tion with the polymer and additionally expand the gal-
lery height;19 this may lead to complete exfoliation of
silicate layers during the processing of polymer nano-
composite. That means organomodification makes clays
compatible with a polymer for the synthesis of nano-
composites. In most cases, to render clays compatible
with other polymers, interlayer cations are exchanged
with cationic–organic surfactants, such as alkylammo-
niums.10,19
Poly(ethylene-co-vinyl acetate) polymers have a
large commercial impact because of their broad spec-
trum of practical applications in different fields: electri-
cal insulation, cable jacketing and repair, component
encapsulation and waterproofing, corrosion protection,
packaging of components, and shoes.20 Different vinyl
acetate contents indeed make ethylene/vinyl acetate
copolymers (EVAs) available as rubbers, thermoplastic
elastomers, and plastics, which in turn provide this broad
spectrum of uses. Because of the high extent of commer-
cial importance, recently researchers have made an
intense focus on EVA composites filled with nanolevel-
dispersed layered silicates. EVA/clay nanocomposites
were first developed contemporarily by Mulhaupt
et al.21 and Srivastava et al.22 After this, many research
groups9,18,23–25 synthesized EVA/clay nanocomposites.
SYNTHESIS AND STRUCTURE OF EVA/CLAY NANOCOMPOSITES
EVAs have been processed into their nanocomposites
with clay minerals by either melt blending or solution
blending by different research groups. In the melt-blend-
ing process, the polymer chains lose their conforma-
tional entropy because of their intercalation between the
clay layers, and this loss of conformational entropy is
probably compensated by enthalpic interactions between
the clay and the polymer, which in turn drive the pro-
cess.26,27 However, in the case of solution blending,
polymer intercalation from a solution is associated with
the entropy gained by the desorption of solvent mole-
cules, which is compensated by the decrease in the confor-
mational entropy of the intercalated polymer chains.26
Two different EVAs containing 12 and 19% vinyl
acetate, abbreviated as EVA-12 and EVA-19, respec-
tively, were processed into their nanocomposites with
synthetic clay fluorohectorite (FH) organomodified by
octadecyl ammonium ion (ODA) and aminododecanoic
acid.21 These materials were melt-blended at 120 8C in a
DACA twin-screw minicompounder to obtain nanocom-
posites. Octadecyl ammonium ion intercalated FH (FH-
ODA) formed a delaminated nanostructure, whereas
ammoniumdodecanoic acid intercalated FH formed a
microcomposite. This means that the octadecyl ammo-
nium ion is more compatible than ammoniumdodeca-
noic acid when intercalated in FH during the synthesis
of EVA-19/FH nanocomposites.
Alexandre et al.9 prepared EVA/clay nanocomposites
from different EVAs with organomodified MMT. EVAs
containing 4.2, 7.1, and 10.8 mol % vinyl acetate were
separately melt-blended (at 130 or 160 8C) with MMT
organomodified by a series of alkylammonium ion and
amine containing carboxylic acids. In this case, di(hy-
drogenated tallow) dimethyl ammonium and dimethyl-
2-ethylhexyl (hydrogenated tallow) intercalated (MMT)
layers exfoliated in the polymer matrix to form nano-
composites, but ammonium ion containing carboxylic
acid moiety intercalated MMT formed microcomposites.
Other EVA/clay nanocomposites23–25 were synthe-
sized by a melt-blending method. Tang et al.24 melt-
blended EVA with organophilic MMTs such as hexa-
decyl and octadecyl ammonium ions at about 145 8C to
obtain EVA/clay nanocomposites. In these EVA/clay
composites, individual silicate layers were exfoliated in
the polymer matrix in a nanometer range along with
some large, intercalated tactoids. Zhang et al.25 also syn-
thesized EVA/clay nanocomposites through a melt-
blending method, taking different EVAs ranging from
thermoplastic elastomers to rubbers with octadecyltri-
methyl ammonium, dioctadecyldimethyl ammonium,
and tricetadecymethyl ammonium ion exchanged MMT.
Interestingly, EVA chains intercalated into the organo-
modified MMT sheets, but in the case of sodium mont-
morillonite (Na-MMT), there was no such intercalation.
However, Li and Ha23 selected maleic anhydride grafted
EVA containing 18 mol % vinyl acetate to process its
nanocomposites with organomodified Cloisite through
melt blending at 175 8C. The dispersion of Cloisite in
the maleic anhydride grafted EVA was much better than
the simple EVA matrix, probably because of the polarity
of maleic anhydride.
EVA/clay nanocomposites22,28–30 were also devel-
oped by the solution blending of EVAs (EVA-12, EVA-
28, and EVA-45 containing 12, 28, and 45% vinyl ace-
HIGHLIGHT 473
tate, respectively) with organomodified MMTs such as
dodecyl ammonium ion intercalated MMT (12Me-
MMT). To observe the dispersion of the clay layers and
morphology, X-ray diffraction (XRD) patterns of an
EVA-12/12Me-MMT composite system and a transmis-
sion electron microscopy (TEM) photograph of an EVA-
12/12Me-MMT composite are displayed in Figures 2
and 3, respectively.30 Na-MMT and 12Me-MMT show
basal reflection peaks at 2h values of 7.4 and 5.68,respectively, corresponding to their respective interlayer
spacings of 1.194 and 1.578 nm. This increase in the
interlayer spacing by 0.384 nm can be attributed to the
intercalation of dodecyl ammonium ions. EVA-12
exhibits no peak in the angle range (2h ¼ 3–108) of
study up to the filler loading of 6 wt %. The disappear-
ance of this peak indicates the delamination or exfolia-
tion31 of aluminosilicate layers of MMT. Upon further
filler loading up to 8 wt %, the EVA-12/12Me-MMT
composite shows a peak in the angle range of 2h ¼ 5–
68, probably because of the aggregation of silicate layers
of clay.8,32 A TEM photograph of this composite shows
that the aluminosilicate layers of MMT are randomly
and homogeneously dispersed on a nanometer scale in
the EVA-12 matrix, supporting directly the formation of
nanocomposites. A similar observation was made for
EVA-19/FH–ODA nanocomposites.21
MATERIAL PROPERTIES
Mechanical Properties
In most of the EVA/clay nanocomposites reported so far
by different research groups, the mechanical properties
in terms of the tensile strength (TS), elongation at
break (EB), elongation modulus, and Young’s modulus
as a function of the clay content have been stud-
ied;9,18,22,24,28–30 these nanocomposites have exhibited
improved mechanical properties. As a typical example,
the tensile properties of EVA-12/montmorillnite nano-
composites30 are described in Figures 4 and 5. TS and
EB of the composites increase significantly with the
introduction of the organoclay into the EVA-12 copoly-
mer matrix. However, this enhancement is maximum
when the clay concentration is only 2 wt %. Upon a fur-
ther increase in the clay concentration up to 4 wt % in
the polymer matrix, TS remains almost constant. This
improvement in TS and EB of the nanohybrids indicates
that the EVA-12 matrix is strengthened by the incorpo-
Figure 2. X-ray diffractograms of (a) Naþ-MMT, (b) 12Me-
MMT, (c) EVA-12, (d) EVA-12 and 2 wt % 12Me-MMT, (e)
EVA-12 and 4 wt % 12Me-MMT, (f) EVA-12 and 6 wt %
12Me-MMT, and (g) EVA-12 and 8 wt % 12Me-MMT.
Reproduced from M. Pramanik et al., Macromol Res 2003, 11,
260, with permission from Polymer Society of Korea.
Figure 3. TEM photograph of a nanocomposite containing
2 wt % 12Me-MMT in an EVA-12 matrix. Reproduced from
M. Pramanik et al., Macromol Mat Eng 2004, 289, 56, with
permission from Wiley-VCH Verlag.
474 J. POLYM. SCI. PART B: POLYM. PHYS.: VOL. 44 (2006)
ration of 12Me-MMT dispersed homogeneously and
randomly in the EVA-12 matrix. The delamination of
the aluminosilicate layers of 12Me-MMT to the nanole-
vel in the polymer matrix offers the whole surface of the
silicate layers for strong interaction with the polymer
chains. This strong interfacial interaction between the
polymer chains and nanolevel-dispersed layers of 12Me-
MMT forms the shear zones when the hybrids are under
stress and strain. The formation of such shear zones is
distinctly supported by scanning electron microscopy
(SEM) images30 [shown in Fig. 6(a,b)] of fracture surfa-
ces of the composites containing 0 and 2 wt % organo-
clay: the fracture surface of the composite containing
0 wt % organoclay exhibits some cracks, whereas no
crack but rather some shear zones on the fracture surface
of the nanocomposite containing 2 wt % organoclay can
be observed, as shown in Figure 6(b). Because of this
strong interaction and development of shear zones, TS
of the nanocomposites is increased. With an increase in
the organoclay loading from 4 to 8 wt % in the EVA-12
matrix, it can be clearly observed that both TS and EB
decrease, and this decrease in TS and EB is probably
due to the aggregation of aluminosilicate layers of clay.
This means, the degree of delamination of aluminosili-
cate layers starts to decrease beyond the 4 wt % filler
loading in the EVA-12 matrix. The aggregation of orga-
noclay particles in the polymer matrix is evidenced by
XRD of the composite with 8 wt % organoclay. Figure 5
depicts the relationship between the modulus at different
elongations and the organoclay content in the EVA-12
matrix. The modulus at 100, 200, and 300% elongations
of the nanocomposites also increases linearly with the
organoclay content in the polymer matrix because of the
strong interaction of aluminosilicate layers with the pol-
ymer chains. Similar improvements in the tensile proper-
ties were observed in EVA/clay nanocomposites,22,28
but this was at a comparatively higher filler loading for
higher vinyl acetate content EVAs such as EVA-28 and
EVA-45. EVA/clay nanocomposites prepared by a melt-
intercalation method9 show that the Young’s modulus of
the nanocomposites increases, but at the same time, both
TS and EB of the nanocomposites slightly fall. It is very
difficult to compare the extent of the improvement of the
mechanical properties of different EVA/clay nanocom-
posites reported so far because EVAs of different vinyl
acetate contents have been processed into their nano-
composites with different clays and different modifying
agents by different methods.
Thermal Properties
The thermal stability of any polymer and its nanocompo-
site is an important property for designing the material
for a particular use in a specific field. In particular, in the
case of nanocomposites, the dispersion of clay particles
in a polymer matrix plays a significant role in changing
the thermal behavior. It has been well established by dif-
ferent research groups that EVAs exhibit two-step
decompositions.21,33 Figure 7 elucidates the effect of
aluminosilicate layers on the thermodegradation of
EVA-12.30 A two-step weight loss of EVA-1233 and its
hybrids can be observed because of two-step decomposi-
tions. The first step corresponds to the deacetylation
reaction, whereas the second one is associated with the
formation of transvinylenes accompanied by the main-
chain scission. The mechanism of this two-step decom-
position has been presented elsewhere.21,33 The thermal
stability of EVA-12 increases with the introduction of
12Me-MMT. The thermal stability of an EVA-12/clay
hybrid with 2 wt % 12Me-MMT is greater. Upon a fur-
Figure 4. TS and EB versus the clay content of EVA-12/
12Me-MMT nanocomposites. Reproduced from M. Pramanik
et al., Macromol Res 2003, 11, 260, with permission from
Polymer Society of Korea.
Figure 5. Variation of the modulus at different elongations
versus the 12Me-MMT content of EVA-12/12Me-MMT
nanocomposites. Reproduced from M. Pramanik et al., Mac-
romol Res 2003, 11, 260, with permission from Polymer
Society of Korea.
HIGHLIGHT 475
ther increase in the 12Me-MMT loading, the hybrids
show a decreasing trend toward their initial thermal
decomposition temperature. Thermogravimetric analysis
(TGA) of EVA-12 and its hybrids shows that the weight
loss in the first step is least when the filler loading is
only 2 wt %. The second-step weight loss decreases with
an increase in the filler content. Figure 7 also explicitly
shows that the overall weight loss of the hybrids is inver-
sely related to the filler loading; that is, the char forma-
tion and the filler loading show a one-to-one correspond-
ence because of the high heat resistance exerted by the
clay. These findings lead to the fact that the EVA-12
matrix is thermally enhanced for lower filler contents
(2 wt % 12Me-MMT) because of homogeneous exfolia-
tion and random dispersion of 12Me-MMT on a nano-
meter level. These nanometer-level-dispersed silicate
layers interact strongly with the polymer chains, and
simultaneously, the barrier effect of silicate layers inhib-
its the mobility of small molecules produced as a result
of thermal degradation. These two effects of silicate
layers together contribute toward the enhancement of
the thermal stability of the nanocomposites. It may be
added here that the higher filler loading destabilizes the
EVA-12 matrix because of the aggregation of silicate
layers (as evidenced through XRD of a hybrid contain-
ing 8 wt % 12Me-MMT), which ultimately provides a
lesser extent of surface area, which, in turn, offers rela-
tively weak interaction with the polymer chains. EVA/
clay nanocomposites22,30 containing more vinyl acetate
Figure 7. TGA of (a) EVA-12, (b) EVA-12 and 2 wt %
12Me-MMT, (c) EVA-12 and 4 wt % 12Me-MMT, (d) EVA-12
and 6 wt % 12Me-MMT, and (e) EVA-12 and 8 wt % 12Me-
MMT. Reproduced from M. Pramanik et al., Macromol Res
2003, 11, 260, with permission from Polymer Society of Korea.
Figure 6. SEM images of fracture surfaces of (a) EVA-12 and
(b) an EVA-12/clay nanocomposite containing 2 wt % 12Me-
MMT. Reproduced from M. Pramanik et al., Macromol Res
2003, 11, 260, with permission from Polymer Society of Korea.
476 J. POLYM. SCI. PART B: POLYM. PHYS.: VOL. 44 (2006)
keep this thermal stability improvement up to 6–8 wt %
filler loadings, probably because of the degree of disper-
sion of clay in the polymer matrices. A similar improve-
ment in the thermal stability has been observed for
EVA/18Me-MMT nanocomposites24 slightly at higher
filler loadings. According to ref. 24, the first step of the
decomposition of EVA/MMT nanocomposites is not
strongly influenced by the catalytic effect offered by the
modifier of the clay. Zanetti et al.21 studied the thermal
degradation of EVA-19/modified FH and MMT nano-
composites in air and in nitrogen. They observed that
both the EVA-19/modified FH and MMT nanocompo-
sites did not show the catalysis of deacetylation in air as
found in nitrogen. This means that exfoliated silicate
layers tend to shield EVA polymers from the action of
oxygen.
Swelling Characteristics
The knowledge of the swelling of a polymer and its
nanocomposites is an important aspect for predicting the
extent of suitability for their applications in a particular
environment. An EVA-28/MMT nanocomposite is given
as a typical example of EVA/clay nanocomposites34 to
observe the effect of the nanodispersion of clay in the
EVA matrix. The swelling indices of nanocomposites
obtained from EVA-28 and 12Me-MMT are displayed
in Figure 8. The insertion of nanometric layers of alumi-
nosilicate in the EVA matrix reduces the swelling indi-
ces of this copolymer, and it varies inversely with the
filler loading. This is due to the inhibiting capability of
clay layers to swell in a solvent. The swelling of a poly-
mer is associated with a general physical phenomenon
called diffusion, by which liquid molecules are first
adsorbed onto the polymer surface and then are trans-
ported from one region to the other. The crosslinks
between polymer chains usually resist the solvent mole-
cules to penetrate the polymer matrix.35 To observe the
effect of aluminosilicate layers on the penetration of
liquid molecules, the crosslink density (defined as the
number of moles of crosslinks per unit of volume) of
nanocomposites can be calculated by the Flory–Rehner
equation.36 Figure 9 presents the effect of aluminosili-
cate layers on the volume fraction and crosslink density
of EVA during swelling.34 Both the volume fraction and
crosslink density of the EVA-28 copolymer in swollen
EVA-28/12Me-MMT nanocomposites are greater than
those of its pure form; that is, the solvent uptake of EVA
polymers tends to decrease when the polymer matrix is
filled with a nanolevel dispersion of clay layers, which
causes a strong interaction with polymer chains because
nanolevel-dispersed clay particles make the whole sur-
face area available for the interaction with the polymer
chains. Indeed, this strong interfacial interaction
between the polymer chains and silicate layers inhibits
the penetration of xylene molecules from the surface to
the bulk region of the nanocomposites, leading to a
reduction of the xylene uptake. In addition, Figure 9
shows that the volume fraction and crosslink density of
the EVA matrix in the swollen mass is increased with
the filler content, and this, in turn, forces a reduction in
the interaction between the polymer chains and solvent
molecules. This is attributed to the fact that the presence
of more nanolevel-dispersed clay particles substantially
imparts polymer–clay interactions. Interestingly, the
crosslink density of the EVA-28/clay system increases
rapidly up to filler loadings of about 4–6 wt %, but upon
further 12Me-MMT loading, the rate of increase in the
crosslink density is quite slow. This is because, beyond
4–6 wt % clay, aluminosilicate layers probably start to
aggregate in the EVA matrix.28,30 Because of this aggre-
gation of silicate layers, the interaction between the poly-
mer chains and silicate layers tends to decrease, and this,
in turn, causes a slow increase in the volume fraction
of the EVA matrix in the swollen gel as well as a slow
increase in the crosslink density. Normally, the swel-
ling of a polymer in a solvent is favored by an increase
in entropy and by a decrease in Gibb’s free energy.
This implies that a high degree of swelling is associ-
ated with the more positive entropy and more negative
Gibb’s free energy of swelling polymers. The free
energy change (DGw) and entropy change (DSw) of
EVA/clay nanocomposites34 for swelling are displayed
in Figure 10. Figure 10 clearly depicts that DGw of
swelling increases with the 12Me-MMT insertions in
the EVA matrix. This means that clay particles dis-
persed on a nanolevel play a negative role in the swel-
ling of EVAs. Such a finding can be attributed to the
Figure 8. Effect of the 12Me-MMT content on the swelling
index of EVA-28/12Me-MMT nanocomposites.
HIGHLIGHT 477
fact that these nanolevel-dispersed clay particles prob-
ably create an environment like a bound polymer with
a polymer matrix, which forces the EVA matrix to
unswell in xylene. The entropy of swelling of these
nanocomposites decreases with the 12Me-MMT con-
tent, as shown in Figure 10, and this indicates the ten-
dency of unswelling in xylene. This means that the
nanolevel-dispersed clay particles hinder the EVA ma-
trix from swelling in xylene as a high degree of swel-
ling is favored by an increase in entropy. Very similar
swelling characteristics have been observed in nano-
composites of EVA-12 and EVA-45 with clay.34
Figure 10. Effect of the 12Me-MMT content on DGw and DSw of the swelling of EVA-28/
12Me-MMT nanocomposites.
Figure 9. Effect of the 12Me-MMT content on the volume fraction and crosslink density of
the swelling of EVA for EVA-28/12Me-MMT nanocomposites.
478 J. POLYM. SCI. PART B: POLYM. PHYS.: VOL. 44 (2006)
Dynamic Mechanical Properties
The dynamic mechanical properties are the mechanical
properties of materials as they are deformed under peri-
odic forces. The polymeric materials under such condi-
tions are often in a dynamic stress and strain field. The
knowledge of the dynamic mechanical properties of poly-
meric materials is therefore indispensable for the design
of these polymers and their nanocomposites. The signifi-
cant role of silicate layers of clay in the storage modulus
(E0) and damping [loss tangent (tan d)] of EVA-28/claynanocomposites37 is presented in Figures 11 and 12. E0
of the EVA-28/MMT nanocomposites increases with the
filler loading in the EVA-28 matrix. The E0 values of anEVA-28/MMT nanocomposite containing 6 wt % are
2.0 � 109 Pa at about 60 8C below the glass-transition
temperature (Tg), 4.8 � 108 Pa at Tg, and 3.5 � 107 at
25 8C above Tg; which are about 1.33, 2.28, and 2.50
times that of pristine EVA-28. This increase in the mod-
ulus results because the silicate layers interact with
EVA-28 chains, strengthening the dynamic modulus.25
Tg of EVA-28/MMT nanocomposites, accompanied by
b relaxation,38 increases slightly at lower filler contents
and decreases with the filler loading. Additionally, the
peak height of tan d decreases with the clay content in
the polymer matrix because of the increasing interaction
between the silicate layers and polymer chains. In the
case of EVA/clay nanocomposites25 prepared by melt
blending, there is also a significant improvement in E0
for EVA/modified-MMT nanocomposites but not for
EVA/Na-MMT microcomposites.
Other Properties and Scope
Fire-retardant materials must be quite resistant to igni-
tion or flame. EVA/clay nanocomposites are also good
fire retardants. Thus, EVA/clay nanocomposites pre-
pared by Duquesne et al.39 exhibited a 50% reduced
peak heat release rate in comparison with pure EVA. As
EVAs are used as packaging and dielectric materials, the
nanolevel dispersion of these silicate layers in these poly-
mer matrices is expected to cause unusual changes in the
gas-barrier, solvent-barrier, and dielectric properties.
These properties are to be investigated because it is
essential to understand them before the design of these
nanocomposites for applications. In our laboratory, we
are investigating these particular properties of these
nanocomposites.
The Ministry of Human Resource Development (New Delhi,
India) and Council of Scientific Industrial Research are grate-
fully acknowledged for providing the financial support to
carry out this investigation smoothly.
Figure 11. E0 versus the temperature for (a) EVA-28, (b)
EVA-28 and 2 wt % 12Me-MMT, (c) EVA-28 and 4 wt %
12Me-MMT, (d) EVA-28 and 6 wt % 12Me-MMT, and (e)
EVA-28 and 8 wt % 12Me-MMT.
Figure 12. Tan d versus the temperature for (a) EVA-28,
(b) EVA-28 and 2 wt % 12Me-MMT, (c) EVA-28 and 4 wt
% 12Me-MMT, (d) EVA-28 and 6 wt % 12Me-MMT, and
(e) EVA-28 and 8 wt % 12Me-MMT.
HIGHLIGHT 479
REFERENCES AND NOTES
1. Wu, Y.; Zhang, L.; Wang, Y.; Liang, Y.; Yu, D.J Appl Polym Sci 2001, 82, 2842.
2. Alexandre, M.; Beyer, G.; Henrist, C.; Cloots, R.;Rulmont, A.; Jerome, R.; Dubois, P. Chem Mater2001, 13, 3830.
3. Wang, H. W.; Chang, K. C.; Chu, H. C.; Liou,S. J.; Yeh, J. M. J Appl Polym Sci 2004, 92, 2402.
4. Vyazovkin, S.; Dranca, I.; Fan, X.; Advincula, R.Polym Mater Sci Eng 2004, 90, 780.
5. Lepoittevin, B.; Devalckenaere, M.; Pantoustier,N.; Alexandre, M.; Kubies, D.; Calberg, C.; Jerome,R.; Dubois, P. Polymer 2002, 43, 4017.
6. Okada, A.; Kawsumi, M.; Usuki, A.; Kojima, Y.;Kurauchi, T.; Kamigaito, O. Mater Res Soc Proc1990, 171, 45.
7. Vaia, R. A.; Ishii, H.; Giannelis, E. P. Chem Mater1993, 5, 1694.
8. Huang, J. C.; Zhu, Z. K.; Ma, X. B.; Qian, X. F.;Yin, J. J Mater Sci 2001, 36, 871.
9. Alexandre, M.; Beyer, G.; Henrist, C.; Cloots, R.;Rulmont, A.; Jerome, R.; Dubois, P. MacromolRapid Commun 2001, 22, 643.
10. Acharya, H.; Pramanik, M.; Srivastava, S. K.;Bhowmick, A. K. J Appl Polym Sci 2004, 93, 2429.
11. Lagaly, G. Solid State Ionics 1986, 22, 43.12. Bala, P.; Samantaray, B. K.; Srivastava, S. K.
Mater Res Bull 2000, 23, 61.13. Bala, P.; Samantaray, B. K.; Srivastava, S. K.;
Haeuseler, H. Z Kristallogr 2000, 215, 235.14. Wang, Z. M.; Nakajima, H.; Manias, E.; Chung,
T. C. Macromolecules 2003, 36, 8919.15. Ma, J.; Yu, Z. Z.; Zhang, Q. X.; Xie, X. L.; Mai,
Y. W.; Luck, I. Chem Mater 2004, 16, 757.16. Noh, M. H.; Jang, L. W.; Lee, D. C. J Appl Polym
Sci 1999, 74, 179.17. Wu, Y.; Zhang, L.; Wang, Y.; Liang, Y.; Yu, D.
J Appl Polym Sci 2001, 82, 2842.18. Alexandre, M.; Beyer, G.; Henrist, C.; Cloots, R.;
Rulmont, A.; Jerome, R.; Dubois, P. Chem Mater2001, 13, 3830.
19. Bala, P.; Samantaray, B. K.; Srivastava, S. K.Mater Res Bull 2000, 35, 1717.
20. Bhowmick, A. K.; Stephens, H. L. Handbook of Elas-tomers, 2nd ed.; Marcel Dekker: NewYork, 2001.
21. Zanetti, M.; Camino, G.; Thomann, R.; Mulhaupt,R. Polymer 2001, 42, 4501.
22. Pramanik, M.; Srivastava, S. K.; Samantaray,B. K.; Bhowmick, A. K. J Mater Sci Lett 2001, 20,1377.
23. Li, X.; Ha, C. S. J Appl Polym Sci 2003, 87, 1901.24. Tang, Y.; Hu, Y.; Wang, J.; Zong, R.; Gui, Z.;
Chen, Z.; Zhuang, Y.; Fan, W. J Appl Polym Sci2004, 91, 2416.
25. Zhang, W.; Chen, D.; Zhao, Q.; Fang, Y. Polymer2003, 44, 7953.
26. Kornmann, X. Ph.D. Thesis, Lulea University ofTechnology, 1999.
27. Mannias, E.; Touny, A.; Wu, L.; Strawhecker, K.;Lu, B.; Chung, T. C. Chem Mater 2001, 13, 3516.
28. Pramanik, M.; Srivastava, S. K.; Samantaray,B. K.; Bhowmick, A. K. J Polym Sci Part B:Polym Phys 2002, 40, 2065.
29. Pramanik, M.; Srivastava, S. K.; Samantaray,B. K.; Bhowmick, A. K. J Appl Polym Sci 2003,87, 2216.
30. Pramanik, M.; Srivastava, S. K.; Samantaray,B. K.; Bhowmick, A. K. Macromol Res 2003, 11, 260.
31. Kornmann, X.; Berglund, L. A.; Sterte, J.;Giannelis, E. P. Polym Eng Sci 1998, 36, 1351.
32. Liu, L.; Qi, Z.; Zhu, X. J Appl Polym Sci 1999, 71,1133.
33. Dutta, S.; Bhowmick, A. K.; Mukunda, P. G.;Chaki, T. K. Polym Degrad Stab 1995, 50, 75.
34. Pramanik, M.; Acharya, H.; Srivastava, S. K.Macromol Mater Eng 2004, 289, 562.
35. Amin, M.; Nasr, G. M.; Attia, G.; Gomaa, A. S.Mater Lett 1996, 28, 207.
36. Encyclopedia of Polymer Science and Engineer-ing, 2nd ed.; Wiley: New York, 1990; Vol. 4.
37. Pramanik, M. Ph.D. Thesis, Indian Institute ofTechnology, 2005.
38. Dutta, S. Ph.D. Thesis, Indian Institute of Tech-nology, 1995.
39. Duquesne, S.; Jama, C.; Bras, M. L.; Delobel, R.;Recourt, P.; Gloaguen, J. M. Comp Sci Technol2003, 63, 1141.
480 J. POLYM. SCI. PART B: POLYM. PHYS.: VOL. 44 (2006)
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