Impact of Low Molecular Weight, Biodegradable, Atactic Amorphous Poly(R, S-Hydroxybutyrate) on Eco-Friendly Poly(Lactic Acid)

Abstract

Poly(lactic acid) (PLA) is attractive, biodegradable, and biocompatible brittle polyester produced from annually renewable natural resources for food packaging and other industrial applications. In this study, blending of PLA with a low molecular weight biodegradable atactic poly(R,S-3-hydroxybutyrate) (R,S-PHB) with different weight ratios was prepared. The influence of the R,S-PHB on PLA's thermal stability and nonisothermal melt crystallization behavior was demonstrated. The TG results showed a considerable drop in the thermal stability of the PLA/R,S-PHB blends compared with neat PLA, but the onset of thermal decomposition is still far from the processing temperature of PLA, indicating that the blended PLA can be safe to process. MDSC technique indicated that PLA is miscible with R,S-PHB up to 30% as evidenced by a single composition-dependent glass transition temperature (obey Fox equation). The DSC and XRD results indicated that the addition of R,S-PHB increased the crystallinity of PLA. Polarized optical microscopy revealed that the spherulitic morphology for the PLA changed from dendrites to banded spherulites for PLA/R,S-PHB. Crystallization kinetics of the nonisothermal crystallization were studied using the DSC technique and analyzed using the Modified Avrami model, which successfully described the nonisothermal crystallization behavior of neat and blended PLA. The nonisothermal crystallization activation energy was calculated based on the Friedman equation, and the results revealed that the blends exhibited lower values than neat PLA.