Defects in polylactide spherulites: Ring line cracks and micropores

Polylactide (PLA) is a representative material in biodegradable polymers, but its application is limited due to the brittleness and poor toughness. In order to investigate the basic brittleness mechanism of PLA, the morphology and formation of spherulite defects in PLA, including ring line cracks with width around 0.3 nm and micropores with diameters of 0.8–1.2 μm, were studied by polarizing microscope and atomic force microscope. The effects of cooling rate, sample thickness, PLA molecular weight, isothermal crystallization temperature and spherulite growth maturity on PLA spherulite defects were discussed. Both ring line cracks and micropores are caused by internal stress caused during PLA melt cooling process, and their morphology would be changed by internal stress distribution with various factors mentioned above. The inhibition of crystal defects will potentially improve the mechanical properties of PLA, thus these results will provide useful references for the toughening modification of PLA.