(13b) Hydrolytic and Thermal Degradation Behavior of Poly(lactic acid)/Zeolite Composites

Poly(lactic acid), PLA, is one of the most important and growing commercial biobased polymers as an alternative to traditional polymers. Thermal and hydrolytic degradation play extremely crucial roles during processing, storage, and after the end-of-life of PLA. This paper presents a study on thermal and hydrolytic degradation behavior of biobased composites based on PLA and natural or synthetic zeolite particles that were produced by a micro-extruder and injection molding system. The hydrolytic degradation behavior was investigated in various aqueous media (distilled water, buffered phosphate solution, and 0.01 N sodium hydroxide solution) at 23, 60, and 90 °C up to several weeks. Characterization involved monitoring weight loss, observing morphological changes using a scanning electron microscope (SEM) and a confocal microscope, and analyzing molecular weight data using gel permeation chromatography (GPC). Changes in crystallinity of PLA and PLA/natural or synthetic zeolite composites were also studied using differential scanning calorimetry (DSC). Thermal degradation behavior of PLA and PLA/natural and synthetic zeolite composites was also investigated using thermogravimetric analysis (TGA). The activation energies for thermal degradation (Ea) were estimated at different weight loss values of 2.5 ? 90 % using Flynn-Wall-Ozawa and Kissinger Methods. Introducing synthetic zeolites into the PLA matrix increases its hydrolytical and thermal degradation compared to introduction of natural zeolites.