Nonisothermal crystallization of poly(L-lactic acid) promoted by polyols

The inherent weak crystallization capacity has an impact on the processability and serviceability of poly(lactic acid) (PLA) and limits its application. D-mannitol (DM) and xylitol (Xy), acting as a nucleation accelerant, were melt-blended with poly(L-lactic acid) (PLLA) and the nonisothermal crystallization behavior was investigated. At 1% dosage, the crystallization temperatures of polyol-modified PLLAs are 10-15? higher than those of neat PLLA in the cooling rate range of 5-20 degrees C. The theoretical half-time of crystallization (t(1/2)) of the Jeziorny model remains constant over the cooling rate range of 10-20 degrees C min(-1), in contrast to the greatly reduced t(1/2) reported for heterogeneous nucleating agents. Xy is more effective than DM in promoting crystallization. It increases the crystallinity of PLLA to similar to 40% within the 1%-5% dosage; and the activation energy of nonisothermal crystallization calculated by the Friendman method follows the order of magnitude: neat PLLA > PLLA/DM > PLLA/Xy. Polyols promote the crystallization of PLLA by a mechanism different from heterogeneous nucleation, providing an efficient and biosafety approach to improve the performance of PLA.