Thermal and mechanical properties of poly(L-lactic acid) poly(ethylene-co-vinyl acetate) blends

Poly(L-lactic acid)(PLLA) was blended with poly(ethylene-co-vinyl acetate)(EVA) and the miscibility of the blend was investigated by DSC, polarizing optical microscopy and rheometry. The blend of PLLA with EVA70, that contained 70 wt% of vinyl acetate, was immiscible because the T-g and the spherulitic growth rate of the blend were nearly constant regardless of the change in the blend composition. On the other hand, the T-g, equilibrium melting temperature, the spherulitic growth rate during the isothermal crystallization of the PLLA-EVA85 blend were decreased with the increase in the EVA content. Moreover, the Flory-Huggins interaction parameter of the blend was found to be negative, which clearly means the PLLA-EVA85 blend was miscible. The tensile strength and modulus of the PLLA-EVA85 blend were dropped rapidly, followed by a more gradual decrease with the increase in the EVA85 content. Strain-at-break, however, was increased rather slowly up to 70 wt% of EVA85 and then increased quite rapidly around 90 wt% of EVA85. (C) 1999 Elsevier Science Ltd. All rights reserved.