Investigation of melt extensional deformation of ethylene-vinyl acetate nanocomposites using...
Transcript of Investigation of melt extensional deformation of ethylene-vinyl acetate nanocomposites using...
Investigation of Melt Extensional Deformation ofEthylene-Vinyl Acetate Nanocomposites UsingSmall-Angle Light Scattering
R. Prasad, Rahul K. Gupta, F. Cser, S.N. BhattacharyaRheology and Materials Processing Centre, School of Civil, Environmental and Chemical Engineering,RMIT University, Melbourne, Australia
Ethylene-vinyl acetate copolymers with vinyl acetate(VA) contents of 9 wt% (EVA9) and 18 wt% (EVA18),and commercially modified montmorillonite clay weremelt blended in a twin-screw extruder to producenanocomposites with various silicate loadings (2.5, 5,and 7.5 wt%). EVA9 was melt compounded with Cloisi-te115A (C15A) and EVA18 was melt compounded withCloisite130B (C30B). Wide-angle X-ray scattering andtransmission electron microscopy have indicated thatEVA9 nanocomposites were predominantly intercalatedin morphology while EVA18 nanocomposites pos-sessed mixed intercalated/exfoliated structures. Lightscattering was conducted in conjunction with melt-drawing experiments to analyze structural evolution ofthe drawn filaments following its exit from the die of asingle-screw extruder. The scattering patterns wereprocessed using Guinier’s approximation. The parame-ter used to characterize deformation was the radius ofgyration of optical inhomogeneities in the direction ofextension and orthogonal to it. The ratio of these radiiof gyration gives the deformation ratio. It was foundthat increasing silicate content decreased the deforma-tion ratio for all the filled EVA18 nanocomposites. EVA9with 2.5 and 5 wt% fillers showed an increase in defor-mation compared with unfilled EVA9, but the 7.5 wt%-filled material showed a decrease. These observationswere attributed to the relatively strong polymer-fillerinteractions. POLYM. ENG. SCI., 49:984–992, 2009. ª 2009Society of Plastics Engineers
INTRODUCTION
The primary mode of polymer melt deformation for
many decades was simple shear; however, in the last 2 to
3 decades, the importance of extensional deformation has
been well recognized [1, 2]. Raible et al. [3] contends that
there are two important reasons for the need to understand
extensional flows of molten polymers and these are (a)
Solidification of polymer melts in industrial operations
frequently involves stretching flows that cause ‘‘frozen-
in’’ strains and stresses, resulting in significant effect on
the properties of the final products; (b) Extensional flows
have for a long time puzzled rheologists when it comes to
the rheological behavior of polymer melts that are very
dependent on the deformations, and show ‘‘shear thin-
ning’’ in shear flows and ‘‘strain hardening’’ in exten-
sional flows.
Very often, in the study of extensional flows, research-
ers use invasive rheological techniques. These techniques
are used to analyze quantitatively, the responses (e.g.
extensional viscosity) of the materials subjected to exten-
sional deformations. The commonly used methods [2, 4]
are: (a) Constant stress measurements that involve sam-
ple-end separation [5] or constant gauge length (improvi-
sation of Meissner-type equipment) [6]; (b) Constant
strain rate measurements that involve sample-end separa-
tion [7]; (c) Continuous drawing experiments (e.g. draw-
ing of an extruded filament) [6].
Another method that has gained some attention in the
analysis of extensional flows is the use of noninvasive
scattering techniques. Giza et al. [8] used wide-angle x-
ray scattering (WAXS) to study the effect of clay on the
crystallization behavior of polyamide 6-clay nanocompo-
sites at high-speed melt spinning. Spruiell and White [9]
used X-ray techniques to carry out experimental investiga-
tions of structure development of melt-spun polyethylene
and polypropylene fibers. White and Cakmak [10] have
provided a critical review of x-ray scattering techniques
(wide and small) used in the study of orientation and
crystallization during melt spinning of polymeric fibers.
Although a number of these scattering techniques
involved X-ray scattering, experimental investigations of
extensional deformations using light scattering techniques
too have been conducted. Li and Larson [11] for instance,
used light scattering to compare deformations of DNA
and polystyrene solutions subjected to shear flow with
that obtained from Brownian dynamic simulations. They
believed that the agreement between the simulation and
experimentation that was obtained for the set of shear
flows could also apply to extensional deformations. Lee
and Muller [12] used light scattering to determine the
Correspondence to: Rahul Gupta; e-mail: [email protected]
DOI 10.1002/pen.21325
Published online in Wiley InterScience (www.interscience.wiley.com).
VVC 2009 Society of Plastics Engineers
POLYMER ENGINEERING AND SCIENCE—-2009
orientation and deformation of polymer chains (high and
low molecular weight polystyrenes dissolved in dioctyl
phthalate) during extensional flow. As expected, there was
strong orientation of the polymer chains in the flow direc-
tion, but lesser amount of chain deformations as was pre-
dicted from elastic dumbbell models. With light scattering,
Menasveta and Hoagland [13] measured the deformation
of dilute polystyrene chains under uniaxial extensional
flows and they too found lower levels of chain deforma-
tions that seemed agreeable with the findings of Lee and
Muller [12]. Chen and Warr [14] examined the light scat-
tering of worm-like micelles in an extensional flow field.
They found that chain alignment in the flow field decreased
after reaching a critical extensional rate. They explained
this decrease to be due to micelle scission at high velocity
gradients.
Most of extensional deformation investigations using
light scattering were conducted on unfilled systems, with
the aim of analyzing orientations and crystallization of
the microstructure during cold drawing or melt spinning
processes. To the authors’ knowledge, there are only two
reported studies on light scattering analysis of polymer
nanocomposites that were subjected to extensional defor-
mation. Yalcin and Cakmak [15] reported on the micro-
structure developed in injection-molded nylon-6 nanocom-
posites. Light scattering was conducted on these samples
on cooling. The other study was conducted in our labora-
tory by the authors [16]. This was a brief study based on
light scattering and rheology of drawn molten EVA (9
wt% vinyl acetate) nanocomposites filled with 2.5 and
5 wt% layered silicates.
In this article, we provide a detailed discussion on light
scattering of EVA (9 and 18 wt% vinyl acetate) nanocom-
posites. Here, an attempt will be made to quantify the ori-
entation and deformation of the system based on the
radius of gyration (Rg) of the scattering domains in the
direction of flow and orthogonal to it. For this purpose,
an online laser light scattering unit has been developed to
study the morphological change and orientation of layered
silicates in an extensional deformation field of polymer
nanocomposites. This technique has been incorporated
into a melt extensional set-up to obtain a ‘‘pictorial’’ view
of the deformation process. Guinier’s approximation was
used to determine Rg.
BACKGROUND ON GUINIER’S APPROXIMATION
The principle of light scattering is similar to that of
other scattering techniques and has been covered at length
in the monographs of van de Hulst [17], Kerker [18], and
Munk and Aminabhavi [19]. Guinier [20] introduced the
concept of ‘‘particle scattering’’ where he demonstrated
that a single colloidal particle could produce diffused X-
ray small-angle scattering, with a maximum at zero angles
[21]. The idea of particle scattering was based on the con-
cept that the angular dependence of scattering is the same
for all particles. The intensity of the scattering at a
macromolecular object of identical particles experiencing
negligible inter-particular interactions (dilute systems) is
simply the sum of all scattering intensities originating from
a single particle. An interesting and often useful feature of
a system that can be derived from the intensities of scat-
tered light, as a function of scattering angle or scalar scat-
tering vector (q) is its radius of gyration (Rg). This can be
achieved using the well-established Guinier analysis
(Guinier approximation) [22]. Considering the fluctuation
in optical densities that causes light scattering, the Rg of
the inhomogeneity or the scattering center can be achieved
without the knowledge of their refractive index [23]. The
Guinier analysis is expressed as shown by Eq. 1.
IðqÞ ¼ Ið0Þexp �q2R2
g
3
!(1)
where q is the scattering wave vector and is as given by
Eq. 2; I(q) is the intensity of scattered radiation; I(0) is theintensity of the incident beam. Munk and Aminabhavi
[19], Guinier and Fournet [22], Higgins and Stein [24],
Sorensen [25] have provided detailed derivation of the
Guinier approximation.
q ¼ 4psinyl
(2)
Pencer and Hallett [26] advocated the use of Guinier
approximation in static small-angle light scattering
(SALS) experiments as opposed to using other means like
discrete Laplace inversions or scattering factors. Using
the Guinier approximation as mentioned earlier does not
require knowledge of shape and associated scattering fac-
tors of the particle. The determination of Rg from Guini-
er’s law proceeds by plotting I(q) versus q to obtain a
Gaussian distribution and a plot of ln [I(q)] versus q2 pro-duces a linear plot with intercept ln [(I0)] and slope of
Rg2/3. The latter plot is also known as the Guinier plot.
For monodisperse, spherical systems, the law is obeyed
over large angular ranges, but where there is departure
from monodispersity or sphericity, the limiting slope as
q ? 0 is still valid and related to the Rg [27, 28].
EXPERIMENTAL MATERIALS AND TECHNIQUES
Materials
The materials that were used in the production of the
polymer nanocomposites were ethylene-vinyl acetate co-
polymer (EVA) and organically modified montmorillonite
clay.
The EVAs used in this project differed in their vinyl
acetate (VA) concentrations, giving rise to dissimilar
properties. The concentrations used were 9 and 18 wt%
VA-based EVA. From this point, these differing EVAs
shall be referred to as EVA9 and EVA18, respectively.
DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2009 985
EVA9 was obtained from Atofina (Australia), while
EVA18 was obtained from DuPont (Australia). Their mo-
lecular weights are as given in Table 1. The presence of
the bulky polar pendent, VA, provides the ethylene back-
bone an opportunity to manipulate the end properties of
the copolymer by varying and optimizing the VA content
[29]. The low VA content copolymers (e.g. 9 wt%) are
essentially a modified low-density polyethylene (LDPE).
It has a reduced regular structure compared to the higher
VA content EVA copolymers.
Two similar types of organically modified montmoril-
lonite (OMMT) clay were used in this project. They were
Cloisites115A and 30B. They shall be referred to as
C15A and C30B for brevity. Both these OMMTs were
obtained from Southern Clay Products [30]. Their differ-
ence lies in the way the natural MMTs were treated to
render them organophilic and hence their compatibility
with the different polymers. C15A was produced by cat-
ion exchange reaction whereby pristine, hydrophilic Naþ-
MMT was modified using dimethyl dihydrogenated tallow
quaternary ammonium chloride (quaternary ammonium
salt). This particular modified clay is considered suitable
for the more hydrophobic polymer such as EVA9. This is
due to the presence of long aliphatic chains that protrude
out of the interlayer walls, thus rendering the originally
hydrophilic MMT, organophilic.
C30B, on the other hand, was a natural MMT (NAþ-
MMT) modified with a ternary ammonium salt known as
methyl, tallow, bis-2-hydroxyethyl quaternary ammonium.
This group of modified MMTs is suitable for the less
hydrophobic polymers like EVA18. Unlike quaternary
ammonium salts, ternary salts possess only a single tallow
group and a lower modifier concentration. The modifier
concentration [30] was 0.9 meq/g-clay for C30B and 1.25
meq/g-clay for C15A.
Nanocomposite Preparation and StructuralCharacterization
The EVA pellets were initially premixed with the
respective OMMTs before introducing into a Brabender
twin-screw extruder. The extruder was operated at 1008Cand at 70 rpm EVA9 and EVA18 nanocomposites with
clay loadings of 2.5, 5, and 7.5 wt% were produced.
Wide-angle X-ray scattering (WAXS) and transmission
electron microscopy (TEM) revealed that EVA9 nano-
composites were intercalated in nature, whereas EVA18
nanocomposites had mixed intercalated/exfoliated mor-
phologies. Details of WAXS and TEM experimentations
and their findings have been reported elsewhere [16, 31].
Also, detailed rheological analyses can be found in our
previous publications [16, 31, 32].
Light Scattering Technique
An optical diffraction unit was designed and built for
use as an on-line monitoring device for investigating ori-
entation and microstructural changes of drawn nanocom-
posite melts [16, 33]. The basic concept of the device is
shown in Fig. 1 below. A solid-state laser with an output
power of 1 mW was used as a monochromatic light
source. The laser beam was focused on the sample to be
tested by a small plastic lens and the noncoherent radia-
tion (reflected light) was filtered out using two pin holes
arranged 50 mm from each other. The scattered beam was
captured on a translucent film. The scattering patterns
were recorded by a digital camera positioned 350 mm
from the screen. The primary beam was excluded by a
beam stop which consisted of a small piece of black
paper adhered to the screen.
To avoid the interfering effects of the environment, the
screen was covered by black paper forming a tube
between the screen and the video camera. All recordings
were done in a dimmed laboratory light condition, which
was the source of some background intensities. The cam-
era recorded the scattering pattern as a function of time
with 25 patterns recorded per second. Data processing
TABLE 1. Molecular weights of EVA9 and EVA18.
Polymer Molecular weight
EVA9 67,320
EVA19 72,600
FIG. 1. Schematic of the laser light scattering (LLS) equipment. As the extrudate descends and pulled by
the twin rollers of the Gottfert Rheotens melt strength tester.
986 POLYMER ENGINEERING AND SCIENCE—-2009 DOI 10.1002/pen
was carried out on individual pictures obtained from the
digital video recordings.
The radius of gyration, Rg, of the scattered particle in
two dimensions was of particular interest and was
obtained by applying Guinier’s approximation as
described earlier. The scattering technique was used to
analyze structural evolution of the drawn molten material
following its exit from the die of a Haake single screw
extruder (Fig. 2). Scattering patterns were obtained at
fixed positions from the die exit at the nip roller accelera-
tion of 12 mm/s2. A computer program was designed by
Cser et al. [33] to analyze the large number of data
obtained. This program calculates a best fit of a Gaussian
function centered at the position of the primary beam to
the measured points. The temperature at the die was set at
1108C for EVA18 and EVA28 nanocomposites, but was
set at 1308C for EVA9 nanocomposites this was con-
firmed using a thermocouple. A higher temperature was
chosen for EVA9 due to the effect of solidification near
the rollers. Note that the melting temperature of EVA9 is
998C, while that of EVA18 is 888C. During the initial
slow velocity, the drawn filament would be expected to
cool at a faster rate. The solidification of EVA9 was
observed during the initial slow drawing velocities. This
effect was not observed for EVA18. At high draw rates,
the extent of ambient cooling of the filament is minimized
and the stretching can be considered nearly isothermal
[31]. A detailed account of the processing been given in
Prasad et al. [16, 31].
Data processing of light scattering runs had to be per-
formed carefully and this was due to the amount of scat-
ter (noise) produced by the data. The noise could be due
to background intensities and/or the amount of optical
inhomogeneities present in the drawn filament. The meas-
ured intensity profile was fitted with a Gaussian curve that
would facilitate further processing. The error involved in
this was within 615%. Radius of gyration of scatters was
evaluated in the direction of draw as well as orthogonal
to it using Guinier approximation as outline in this manu-
script. Although the radii of gyration (both directions)
seem scattered, they do follow a linear fit to within
615% to 620% error. The data presented in the manu-
script will be based on the linear fit and only qualitative
discussions were made.
RESULTS AND DISCUSSION
Light scattering was used as a technique for investigat-
ing the deformation of molten drawn fibers of EVA9 and
EVA18 nanocomposites. The data processing yielded
about a hundred data points for each sample tested. A
typical two-dimensional scattering image obtained is as
shown in Fig. 3. The horizontally oriented pattern is asso-
ciated with oriented scattering particle or inhomogeneity.
Note that scattering is a consequence of an inhomogene-
ous optical density of the material [34, 35]. Norris and
Stein [36] explained that these scattering patterns have
the highest intensity perpendicular to that of the greatest
dimension of the scattering particle. It is due to this
inverse relationship that the highest length scale (horizon-
tal) in the scattering images, as shown in Fig. 3, corre-
sponds to the direction orthogonal to the stretch axis or
machine direction. It is essential to mention at this point
that the intention of using SALS and Guinier’s law in this
work was to enable the investigation of the deformation
process and no attempt was made to relate the analysis to
the composition of the optical inhomogeneities.
The particle scattering component was processed using
the Guinier concept, that is, Gaussian curves were fitted
to the central part of the scattering pattern according to
the two directions with respect to stretch [16]. The verti-
cal axis of Fig. 3 corresponds to the direction of stretch.
The radius of gyration, Rg, of the scattering particle was
then calculated according to the Guinier concept (Eq. 1above). To ascertain the validity of Guinier’s approxima-
tion to the EVA nanocomposites, it is imperative that two
conditions be satisfied: (a) There is a linear fit between
ln[I(q)] and q2 at low q, corresponding to small scattering
angles; (b) qRg \ 1.
FIG. 2. Schematic of Gottfert Rheotens melt strength tester.
FIG. 3. Light scattering image of 7.5 wt%-filled EVA9 filament drawn
at 1308C with a nip roller acceleration of 12 mm/s2. [Color figure can be
viewed in the online issue, which is available at www.interscience.wiley.
com.]
DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2009 987
Figures 4 and 5 are Guinier plots for EVA9 and
EVA18 with 7.5 wt% fillers. These figures also show how
the Guinier’s zone (that is within the limit of linearity)
has been determined. However, beyond this limit of line-
arity, where qRg [ 1, Guinier’s approximation does not
apply. We believe that the method has worked in our case
because (1) there is a linear fit at low q and (2) qRg \ 1.
The Rg has been calculated from the slope of the linear
region. Table 2 provides a list of Rg values parallel (Rg||)
and orthogonal (Rg\) to the direction of extension just
below the die exit at the start of extension process.
An average Rg, both in the direction of extension and
orthogonal to it has been plotted as shown in Figs. 6 and
7 for 5 wt%-filled EVA9 and EVA18 nanocomposites,
respectively. A linear least square fit was drawn through
the points to establish an average for all the positions
studied. This fit is equivalent to a master curve of the
deformation experienced by the drawn material [16]. The
Rg was plotted as a function of total extensional strain as
experienced by each material element, which is as defined
in Eq. 3. The ratio in the parentheses is simply the draw
or stretch ratio, where vw is the velocity of the Rheotens
nip rollers and v0 is the extrudate velocity.
e ¼ lnnwn0
� �(3)
It is clear from these figures that the deformation expe-
rienced by the drawn filament at any point is uniaxial
because Rg corresponding to the direction perpendicular
to extensional axis remains almost unchanged with exten-
sional strain. The greatest amount of deformation is expe-
rienced in the direction of extension or draw.
Figures 8 and 9 show deformation ratios (Rg||/Rg\) as a
function of extensional strain, and it describes the extent
of deformation experienced by the drawn material. It is
interesting to note from these figures that there was an
increase in deformation ratio for the unfilled EVA poly-
mers with increasing extensional strains. It may seem
conceptually inconceivable that unfilled EVA melts are
compositionally inhomogeneous to produce SALS patterns
under normal molten conditions. However, this could be
FIG. 4. Guinier’s law plot of EVA9-C15A (7.5 wt%) nanocomposite
fitted to SALS raw data. Data obtained just below the die exit at the start
of extensional process.
FIG. 5. Guinier’s law plot of EVA18-C30B (7.5 wt%) nanocomposite
fitted to SALS raw data. Data obtained just below the die exit at the start
of extensional process.
TABLE 2. Radius of gyration (Rg) obtained for both directions near
the die exit at the start of experiment as calculated from the linear
region of Guinier plot of the raw data.
EVA9 Rg\ (lm) Rg|| (lm) EVA18 Rg\ (lm) Rg|| (lm)
0 wt% 1.19 2.35 0 wt% 0.57 0.65
2.5 wt% 1.20 2.24 2.5 wt% 0.735 0.81
5 wt% 0.99 2.14 5 wt% 0.66 0.70
7.5 wt% 0.33 0.41 7.5 wt% 0.44 0.47
FIG. 6. Radii of gyration of scattering particle orthogonal and in the
direction of extensional deformation for the 5 wt% EVA9 nanocomposite
(Rheotens at 1308C). Linear least square fit for all positions studied.
988 POLYMER ENGINEERING AND SCIENCE—-2009 DOI 10.1002/pen
due to two possible reasons: (a) Convergent flows in the
die result in inhomogeneities within the melt. These flows
are a combination of extension and shear forces; (b) The
SALS patterns were recorded at the start of the extension
process. The stretching of the melt by the nip rollers of
the Rheotens melt strength tester would have imparted
further deformation.
Therefore, the presence of either or both reasons could
in fact result in the formation of such inhomogeneities.
Moreover, these inhomogeneities are due to difference in
optical densities within the melt. To further our case that
the SALS patterns were in fact due to the aforementioned
reasons, light scattering experiments were conducted on
annealed unfilled EVA melts. SALS patterns were not
detected for annealed samples, thus confirming that such
patterns were due to the deformations imparted on the
melt due to the reasons above. The result of this experi-
ment has been mentioned in an earlier work [16]. More-
over, as mentioned in our previous work [16], SALS pat-
terns were also observed for other unfilled polymer melts
like LDPE and PP undergoing the Rheotens extensional
deformation.
The light scattering results did produce some interest-
ing observations. From Fig. 8, clearly, EVA9 with 2.5
and 5 wt% filled systems produced high deformation
ratios compared with the unfilled EVA9. This is, however,
not observed for EVA9 with 7.5 wt% loading and all
EVA18 nanocomposites (when compared with unfilled
EVA18). For EVA9 with 2.5 and 5 wt% nanocomposites,
it could be seen that their deformation ratios are much
higher than that of the unfilled polymer as the experiment
proceeded toward rupture of the drawn filament. The ini-
tial deformation ratios of the nanocomposites tested were
nearly identical to that of the unfilled material as at this
stage the drawing process was just starting. The diffrac-
tion patterns obtained here were nearly circular for all
materials studied suggesting that the only form of defor-
mation here originated in the die (Fig. 10a). As the
experiment proceeded, the deformability of the two filled
systems was almost identical to each other, but higher
than that of the unfilled material. The higher extent of
deformability is possibly due to increased orientations of
dispersed particles [16].
The different observations offered by 7.5 wt%-filled
EVA9 and all the EVA18 nanocomposites may be
explained in terms of structural evolution during the de-
formation process. It must be reiterated that scattering
FIG. 7. Radii of gyration of scattering particle orthogonal and in the
direction of extensional deformation for the 5 wt% nanocomposite
EVA18 (Rheotens at 1108C). Linear least square fit for all positions
studied. [Color figure can be viewed in the online issue, which is avail-
able at www.interscience.wiley.com.]
FIG. 8. Deformation ratio as a function of extensional strain for EVA9
nanocomposites at various silicate loadings undergoing extensional de-
formation (Rheotens at 1308C). Linear least square fit for all positions
studied.
FIG. 9. Deformation ratio as a function of extensional strain for
EVA18 nanocomposites at various silicate loadings undergoing exten-
sional deformation (Rheotens at 1108C). Linear least square fit for all
positions studied.
DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2009 989
patterns captured as shown in Fig. 3 was a result of ori-
ented inhomogeneities. Compare these images with that
of EVA9-5 wt% (C15A) as shown in Fig. 10. The main
difference is in their scattering intensities. The high scat-
tering intensities as shown in Fig. 10 relates to the fact
the inhomogeneities in this filled system were able to ori-
entate strongly in the direction of stretch. The higher con-
centration of oriented scattering fillers acts as scattering
centers, giving out strong scattering intensities.
On the other hand, the EVA9 with 7.5 wt% silicate
and all the filled EVA18s did not produce a high level
scattering intensity. This effect possibly corresponds to a
lower degree of orientation. This, of course, does not
mean that there was no orientation, but the extent of ori-
entation in the stretch direction was not as significant
compared to the unfilled EVA9 and EVA18 samples and
EVA9 with 2.5 and 5 wt% layered silicates. Figures 11
and 12 illustrate intensity profiles of EVA9 and EVA18
nanocomposites as a function of q. Both figures show that
unfilled EVA9 and EVA18 produced scattering intensities
that follow a Gaussian profile. Note that the profiles
shown in both figures are Gaussian fits of the original in-
tensity profiles, and it can be concluded that intensity
decreases with the addition of layered silicates.
A possible reason for this response in the case of
EVA9 with 7.5 wt% and EVA18 nanocomposites is the
relatively strong polymer-filler interactions. As in the case
of shear and extensional rheology [16, 31, 32], where it
was reported that EVA18 systems showed enhancements
in melt flow properties, the importance of interactions
between polymer-filler and filler-filler could not simply be
underestimated. It is strongly believed that the polymer-
FIG. 10. Morphological evolution of scattering particle undergoing uniaxial extension Rheotens at 1308Cand nip roller acceleration of 12 mm/s2 (EVA9 with 5 wt% silicate loading). [Color figure can be viewed in
the online issue, which is available at www.interscience.wiley.com.]
FIG. 11. Intensity profile as a function of scattering vector, q, for
EVA9 nanocomposites. Data obtained just below the die exit at the start
of extensional process.
FIG. 12. Intensity profile as a function of scattering vector, q, for
EVA18 nanocomposites. Data obtained just below the die exit at the
start of extensional process.
990 POLYMER ENGINEERING AND SCIENCE—-2009 DOI 10.1002/pen
filler interactions restrict the mobility of the EVA18
chains as also their ability to fully align in the direction
of flow. Further, as silicate content was increased, filler-
filler interactions become prominent, both in two-dimen-
sional as well as in three-dimensional. Two-dimensional
interactions take place when the fillers align in the stretch
axis, which is manifested as the orientation as observed in
EVA9 with 2.5 and 5 wt% fillers. But on increasing filler
loading as in the case of EVA9 with 7.5 wt% and EVA18
nanocomposites, the filler-filler interactions become prom-
inent and may also lead to their restricted motion. Laun
[37] explained using glass fiber composites that the num-
ber of adjacent particles governs the free rotation of fill-
ers. Collision with neighboring fillers plays an important
role in the free movement, which will strongly affect
average filler orientations [38]. Moreover with increased
filler loading, the reduction in this free movement is man-
ifested in the reduced alignment of scattering centers
(combination of polymer and filler) and this is reflected in
the reduced deformation ratio as shown in Figs. 8 and 9.
This reduction in free movement and increase in filler-
filler interactions may possibly lead to physical
‘‘jamming’’ of the fillers (Fig. 13) and consequently
increased draw force and reduced drawability as the sili-
cate content was increased [16, 31, 32]. One can also
infer that the restricted mobility of polymer chains and
silicate layers reduces the ability for alignment or orienta-
tion, thus causing lower scattering intensities.
Interestingly, these results showed that the decrease in
intensities of the scattering patterns and extent of deforma-
tion for 7.5 wt%-filled EVA9 and all EVA18 nanocompo-
sites depended very much on the extent of polymer-filler
interactions and not quite on the final morphologies. At the
highest silicate loading for the predominantly intercalated
EVA9, scattering intensities were qualitatively similar to
that of EVA18 nanocomposites at even the lowest loading
(2.5 wt%), which was deemed to possess mixed interca-
lated/exfoliated morphologies. It must therefore be noted
that the extent of interaction between polymer-filler and fil-
ler-filler plays a significant role in shaping the final proper-
ties of the filled system. It can generally be concluded that
exfoliated systems therefore have more significant poly-
mer-filler interactions compared to intercalated ones. For
the intercalated systems to have such high degree of inter-
actions, a higher concentration of filler would be required.
CONCLUSIONS
Polymer nanocomposites were prepared by melt blend-
ing EVA9 and EVA18 with Cloisite115A and Cloisi-
te130B, respectively. EVA9 nanocomposites were found to
be intercalated, whereas EVA18 nanocomposites were
found to possess mixed intercalated/exfoliated morpholo-
gies. Light scattering tests were conducted in conjunction
with melt drawing experiments to analyze structural evolu-
tion of the drawn molten material following its exit from
the die of a single-screw extruder. Guinier’s law was used
to investigate the deformation process and relate the radii of
gyration of optical inhomogeneities to the extensional strain
imparted. It has to be reiterated that the technique was not
used to analyze composition of the inhomogeneities. Gener-
ally, it was shown that the technique could be used to inves-
tigate and understand the effect(s) of the deformation
process on the microstructure of the material in question.
Specifically, it was found that increasing silicate content
decreased the deformation ratio (extent of deformation) for
EVA9-7.5 wt% C15A and for all the filled EVA18 nano-
composites. EVA9 with 2.5 and 5 wt% showed an increase
in deformation ratio compared with unfilled EVA9.
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