Improvement in impact resistance of polylactic acid by masticated and compatibilized natural rubber

Abstract

Mastication is the technique widely used to reduce viscosity of natural rubber and the higher mastication speed leads to lower NR viscosity. The optimum viscosity of NR that could provide high impact strength for the blends depends largely on the blending time and method. This study is focused on the enhancement of impact strength of polylactic acid (PLA) blended with masticated natural rubber (NR) using sorbitan ester (SE), a biodegradable food additive, as a compatibilizer. The effects of NR mastication, compatibilizer and NR contents and the mixture’s viscosity on the morphological, thermal and impact properties of PLA/NR blends were investigated in relation to the changes in the morphology, thermal properties and impact strength of PLA/NR blends. It was found that the optimum viscosity of NR that provided the highest impact strength to the blends was achieved when NR was masticated at 40 rpm for 15 min. The highest impact strength corresponded well not only with the small NR phase size, but also with the highest crystallization rate. For the effect of compatibilizer, it was found that a small amount of SE could more than double the impact strength of the blends, where the optimum compatibilizer content was 0.5 wt%. Interestingly, the high impact strength of the blends in all cases was accompanied by short interparticle distance and slightly higher percent crystallinity.