Melt compounding and characterization of poly(lactide) stereocomplex/natural rubber composites

Poly(lactide) (PLA) is an interesting biodegradable polymer but has limited application because of its brittleness and low thermal stability. We found that both drawbacks of PLA were solved by forming stereocomplexes augmented with natural rubber (NR). Equal amounts of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) stereoisomers were blended to form a stereocomplex (St-PLA). Varying amounts of NR (5-30% by weight) were added simultaneously to equal amounts of the stereo isomers by melt blending. FTIR and XRD spectra demonstrated that, despite the added NR, the stereocomplex structures were still generated and complete. Stereocomplex crystallinity decreased with increasing NR content, verified by DSC and XRD, as well as polarizing optical micrographs which showed fewer spherulites at higher NR content. Measured glass transition temperatures (T-g) of St-PLA/NR blends were significantly lower than for neat St-PLA, exhibiting shifts to as low as 46 degrees C at 30%wt NR content, because of rubber dispersed in St-PLA segments expanding the free volume and enhancing chain mobility. Thermal stability of the blends, estimated by TGA, showed desired results, for example, at the 50% weight loss point, the temperature of all St-PLA/NR blends moved to higher temperatures than neat St-PLA. POLYM. ENG. SCI., 2017. (c) 2017 Society of Plastics Engineers