Cryogenic Impact-Induced\nPulverization Process for\nFast, Highly Crystallized, and Nucleating Agent-free PLA with High\nHeat Resistance

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