Compatible blends of thermoplastic starch and hydrolyzed ethylene-vinyl acetate copolymers.

Ethylene-vinyl acetate copolymer (EVA) with 19% of vinyl acetate and its derivatives modified by hydrolysis of 50 and 100% of the initial vinyl acetate groups were used to produce blends with thermoplastic starch (TPS) plasticized with 30 wt% glycerol. The blends were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, water absorption, stress-strain mechanical tests, dynamic mechanical analysis and thermogravimetric analysis. In contrast to the blends with unmodified EVA, those made with hydrolyzed EVA were compatible, as demonstrated by the brittle fracture surface analysis and the results of thermal and mechanical tests. The mechanical characteristics and water absorption of the TPS were improved even with a small addition (2.5 wt%) of hydrolyzed EVA. The glass transition temperature rose with the degree of hydrolysis of EVA by 40 and 50°, for the EVA with 50 and 100% hydrolysis, respectively. The addition of hydrolyzed EVA proved to be an interesting approach to improving TPS properties, even when very small quantities were used, such as 2.5 wt%.