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.]


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


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.


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.


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


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.


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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Investigation of melt extensional deformation of ethylene-vinyl acetate nanocomposites using...

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