Highly Enhanced Nucleating Effect of Melt-Recrystallized Stereocomplex Crystallites on Poly(L-lactic acid) Crystallization

In the general processing temperature range of poly(L-lactic acid) (PLLA) articles (210-240 degrees C), PLLA/poly(D-lactic acid) (PDLA) stereocomplex (SC) crystallites melted just above the endset temperature of SC melting (228-238 degrees C) and recrystallized during cooling were found to act as the most effective nucleating agents for enhancing the crystallization of PLLA compared to partially melted SC crystallites (211-227 degrees C) or those melted far above the endset temperature of SC melting (240 and 250 degrees C) and recrystallized during cooling. The high nucleating effect of the SC crystallites melted in the temperature range of 228-238 degrees C was found to be caused by their smaller sizes or the larger number of SC crystallites per unit mass. The incorporation of such SC crystallites facilitates the processing of PLLA articles having high crystallinity and, therefore, high heat-resistance in a shorter period to reduce the production cost.