PLLA/ABS Blends Compatibilized by Reactive Comb Polymers: Double Tg Depression and Significantly Improved Toughness

A reactive comb (RC) polymer, which was composed of one poly(methyl methacrylate) (PMMA) backbone, two PMMA side chains and a few epoxy groups that distributed randomly along the backbone, was applied as a compatibilizer in an immiscible poly(l-lactic acid)/acrylonitrile-butadiene-styrene) system (PLLA/ABS). The morphological structures, the rheological, mechanical and thermal properties of the obtained PLLA/ABS blends were investigated systematically. For the first time in the reactive compatibilized system, we found that the glass transition temperature (Tg) of both PLLA and ABS phase depressed to lower temperature and the toughness of the compatibilized PLLA/ABS blend was significantly improved. The effect of blending composition showed that both the depression of Tg and the improvement of toughness were most significant at the weight ratio of 50/50, at which the area of PLLA/ABS interface was the largest. It is considered that the in-situ formed PLLA grafted RC polymers at the PLLA/ABS interface drastically improved the interfacial adhesion between the two phases. Thus the internal pressure, derived from the differentiation of the thermal contraction between the PLLA and ABS phase during cooling from the melt, significantly enhanced the mobility of the molecular chains of the both components on a microscopic scale, which was manifested by a double Tg depression phenomenon on a macroscopic scale. This investigation revealed that both the interfacial adhesion and asymmetric thermal shrinkage are important for the toughening of a rigid/rigid polymer blend.