Influence of screw speed on the mechanical and rheological properties of poly(ethylene-co -vinyl acetate)-organomodified montmorillonite nanocomposites

Abstract

Poly(ethylene-co-vinyl acetate) (EVA) and organophilic montmorillonite clay nanocomposites were manufactured in a co-rotating twin-screw extruder using screw speeds ranging between 200 and 800 rpm. The morphology and thermal-mechanical and rheological properties were studied to establish processing–morphology–property relationships. Particularly for samples produced under higher screw speed ranges, X-ray diffraction and transmission electron microscopy revealed a tendency of increased exfoliated clay. Although the mechanical properties improved by the presence of clay, they were not altered by the screw speed. The rheological behavior in the solid and melt states were evaluated and showed that the storage modulus of neat EVA subjected to higher screw speed undergoes more pronounced decrease in the storage modulus than the nanocomposites, suggesting that the clay minimizes the effect of the screw speed. This minimization effect could be explained in the light of the assessment of relaxation times that showed stronger physical interactions with the nanocomposites in the molten state. POLYM. COMPOS., 36:854–860, 2015. © 2014 Society of Plastics Engineers