Cryogenic Impact-Induced Pulverization Process for Fast, Highly Crystallized, and Nucleating Agent-free PLA with High Heat Resistance

Biodegradable polymers such as poly(lactic acid) (PLA) are expanding into wider fields as substitutes for nonbiodegradable plastics. However, a viable option to improve the crystallization and heat resistance properties of PLA in the industry is the use of nonbiodegradable nucleating agents. Thus, this study presents a preprocessing method for enhancing PLA properties while maintaining biodegradability without using nucleating agents. The PLA preprocessed with cryogenic impact-induced pulverization (CIIP) demonstrates a self-nucleation (SN) behavior. This SN effect was systematically investigated by examining the crystallization during the molding process under various CIIP conditions. As a result, the crystallinity of CIIP-treated PLA increased by 36.2% through densely organized nucleation sites, and the crystallization rate was 80.1% faster at 8.5 min compared to pellet-type PLA (42.8 min). Additionally, the SN effect induced through the CIIP process preserved the stable crystal structure, improving crystallization even with repeated melting. The improved melt-recrystallization behavior by SN agents was evident in injection molding. Consequently, the heat distortion temperature (HDT) increased, improving heat resistance by up to 81.3%. These effects are expected to be practical for improving productivity and quality during the injection molding process. Therefore, this study can expand the scope of biodegradable and sustainable materials by applying PLA with the SN effect realized through the CIIP process to various fields.