Natural Weathering of Poly (Lactic Acid): Effects of Rice Starch and Epoxidized Natural Rubber

Poly(lactic acid) (PLA) composites consisting of PLA, rice starch (RS), and epoxidized natural rubber (ENR50) are compounded using a twin-screw extruder followed by compression molding. Two types of thermoplastic starch are prepared by mixing RS with glycerol and water. Natural weathering tests are performed on the PLA/RS composites in Penang, Malaysia for 2 months. The average mean temperature and mean relative humidity are 29 degrees C and 70%, respectively. Tensile tests are performed to characterize the mechanical properties of the weathered PLA/RS composites. Morphological studies are performed by using scanning electron microscopy (SEM). The tensile properties of weathered PLA/RS composites decreased slightly, on the other hand, the tensile properties of weathered PLA/SG and PLA/SGW composites decreased drastically. The retention-ability of the PLA composites are relatively low, which may be attributed to the photo-degradation of PLA, chain scission of PLA, oxidation degradation on ENR, moisture absorption of RS, and leaching of RS particles. In addition, discoloration, surface roughness, surface cracking, and embrittlement are observed for all PLA/RS composites. The extent of degradation is increased by the addition of ENR, owing to the fact that ENR is susceptible to oxygen attack, and consequently facilitates degradation. The morphological properties of the weathered PLA/RS composites are transformed to a more brittle behavior, indicating that severe degradation has occurred on the PLA/RS composites.