MORPHOLOGY AND VISCOELASTIC BEHAVIOR OF POLYLACTIDE/ETHYLENE-VINYL ACETATE COPOLYMER BLENDS

Polylactide/ethylene vinyl acetate copolymer blends (PLA/EVA) with various blend ratios were prepared by melt mixing. The phase morphology and viscoelastic properties of the blends were then studied using scanning electron microscope (SEM), selective etching and rheometer, respectively. The results show that the PLA/EVA blends are typical thermodynamically immiscible blends with interfacial tension values of about 2.2 mN/m between the two polymers. Hence the blend systems present sea-island and co-continuous morphology at various blend ratios. The phase inversion content of EVA component is about 50 wt% similar to 60 wt%, which is in agreement with the results predicted by the viscous model. In contrast to that of the blend with co-continuous morphology, the linear viscoelastic response of the blend with sea-island morphology can be better described by the emulsion model. The relatively wide region of phase inversion of the PLA/EVA blend systems is mainly attributed to the rather high elasticity ratio between the two polymers and also to the yielding behavior of EVA.