Influence of Non-isothermal Melt Crystallization on the Thermal Behavior and Morphology of Poly-L-lactide

The influence of non-isothermal melt crystallization on thermal behavior and morphology of poly-L-lactide (PLLA) was investigated by differential scanning calorimetry (DSC), polarizing micrograph (POM), and scanning electron microscopy (SEM). Crystallization performed at lower cooling rate (2 °C·min−1) was accompanied by a change of the kinetics around 118 °C. The glass transition temperature of PLLA decreased with the increase in cooling rate. The crystallinity at the end of crystallization and the size of PLLA spherulites increased with decrease in cooling rate, and PLLA became almost amorphous when cooled at a rapid rate of 10 °C·min−1. PLLA biodegradable material with a spherulite structure was obtained by using a compression mould and controlling the cooling rates, and spherulites developed rapidly at lower cooling rates. The fracture surfaces of PLLA at low cooling rates were more compact and smoother, but more brittle, than those at high cooling rates.