Nucleating Agents to Enhance Poly(L-lactide) Crystallization and Melting Behavior of Modified Poly(L-lactide)

Melt processing poly(L-lactide) (PLLA) with a nucleating agent has been thought to be one of the most effective route to enhance PLLA s crystallization and heat resistance. In the current work, a newly-developed organic nucleating agent named N, N -bis(2-picolinyl) 1, 4-naphthalenedicarboxylic acid dihydrazide (NCAPH) was synthesized to investigate its effects on PLLA�s crystallization and melting behaviors. It is proved that NCAPH as an organic crystallization nucleating agent could provide large number of crystallization nucleation sites to improve PLLA�s crystallization, as observed from DSC and POM measurements. The result from melt-crystallization processes further showed that the final melting temperature and cooling rate were two important factors for affecting PLLA�s melt-crystallization behaviors in cooling, and the theoretical calculation result of frontier orbital energy indicated there existed probable intermolecular interaction between N-H of NCAPH and C=O of PLLA, which was proposed as nucleation mechanism of NCAPH for promoting PLLA�s crystallization. The melting behaviors of PLLA/NCAPH after non-isothermal crystallization or isothermal crystallization further confirmed the positive effects of NCAPH and NCAPH�s loading for the crystallization of PLLA, meantime, the melting behaviors depended on the heating rate, crystallization temperature, crystallization time, etc.