Effects of gamma irradiation on the crystallization, thermal and mechanical properties of poly(l-lactic acid)/ethylene-co-vinyl acetate blends

Abstract

Poly(l-lactic acid)/ethylene vinyl acetate polymer blends (PLLA/EVA) with various blend ratios were prepared through melt blending process. The structural-property behavior of the polymer blends before and after they had been exposed to gamma irradiation was investigated. The hydrolytic degradation was investigated. The interfacial interaction between PLLA and EVA was visualized by Mechanical testing and FTIR. The crystallization behaviors of the blends were investigated by Differential scanning calorimetry (DSC), and the thermal stability was studied by thermogravimetric analysis (TGA). The results show that the hydrolytic degradation rate of PLLA/EVA blend can be widely controlled by exposing the PLLA/EVA to gamma-irradiation and also by EVA content. In alkaline solution, the hydrolytic degradation rate of the blends exposed 100 kGy and whose EVA content is higher than 50 wt% was decelerated while the rate of the unirradiated blends whose EVA content is lower than 20 wt% was accelerated. The tensile strength and modulus of the PLLA–EVA blend were increased by increasing PLLA content in the polymer blends and irradiation dose. FTIR spectra showed that some modifications occurred, after they had been exposed to gamma irradiation. The crystallization behavior was studied with differential scanning calorimetry and the composition-dependent changed of degree of crystallinity (Xc) of the PLLA phase indicated that PLLA and EVA were immiscible over the composition range investigated. However, there is a sharp decrease in the crystallinity with increasing EVA and irradiation dose. The TGA thermograms showed that the irradiated blends were less thermally stable than the unirradiated blends, at higher temperatures, the opposite situation was seen.