Extensibility of EVA Based Nanocomposites
Ranjit Prasad, Rahul K. Gupta, Ferenc Cser and Sati N. Bhattacharya*
Rheology and Materials Processing Centre,
School of Civil and Chemical Engineering,
RMIT University, Melbourne, Australia
The structure and deformation
characteristics of ethylene-vinyl acetate (EVA)-layered silicate nanocomposites
were studied using steady shear and extensional rheology. EVAs with VA contents
of 18% and 28% by weight and a commercially modified montmorillonite clay were
melt compounded in a twin-screw extruder. Nanocomposites of 2.5%, 5% and 7.5%
by weight were produced. WAXS measurements have revealed that EVA chains had
intercalated into the silicate layers and expanded the interlayer distance. TEM
showed that the morphologies of the nanocomposites were of mixed
intercalated/exfoliated. The nanocomposites exhibited an increase in steady
shear viscosities compared to the unfilled EVA polymers. At high loading there
was a possibility of yield stress owing to network structures. Elasticity of
the nanocomposites was compared using first normal stress difference-shear
stress plots and the modified Cole-Cole plots, with both methods showing
contradictory results. Melt strengths of both EVAs were enhanced with the addition
of silicate fillers; however, this was at the expense of the materials’
extensibility. Addition of silicate fillers also brought with it flow
instabilities like draw resonance and ductile failure, both of which lead to
limitations in polymer processing.
Keywords: EVA Nanocomposites, Shear Rheology, Elasticity, Melt
Strength, Extensional Viscosity, Draw Resonance
*
Corresponding author Tel: +61-3-9925-2086; Fax:
+61-3-9925-2268
E-Mail address: Satinath.Bhattacharya@rmit.edu.au