A comparison of crystallization behavior for melt and cold crystallized poly (l-Lactide) using rapid scanning rate calorimetry

A unique rapid scanning rate differential scanning calorimeter is used to examine the differences in melt and cold crystallized poly (l-Lactide) (PLLA), a biodegradable semi-crystalline polymer. After isothermal melt and cold crystallization at various temperatures, both melt and cold crystallized PLLA are characterized by similar melting temperatures (Tm) and exhibit multiple melting behavior on heating at 500 °C/min. However, cold crystallization results in a higher degree of crystallinity (wc) compared to melt crystallization. While the overall amorphous fraction is higher for melt crystallization, the mobile amorphous fraction (wa) is found to be higher for cold crystallization. The rigid amorphous fraction (wraf) in PLLA is determined to be higher for melt crystallization than for cold crystallization at almost all temperatures. The higher values of wraf also appear to result in higher values of the glass transition temperature (Tg) for melt crystallized samples due to a reduction in mobility of amorphous phase. These dramatic differences depending on whether the material is brought to the crystallization temperature from the melt or the glassy state, could have profound implications for processing and optimizing the properties of PLLA.