Synergistic effect of stereocomplex crystals and shear flow on the crystallization rate of poly(l-lactic acid): A rheological study

Abstract

Stereocomplex (SC) is a very interesting crystal modification formed between enantiomeric polymers, such as poly(L-lactic acid) (PLLA) and poly(D-lactic acid). Here, by a rheological approach, we found that SC and shear flow can give rise to a notable synergistic effect on the crystallization rate of PLLA. Moreover, the PLLA containing stereocomplex was found to be more sensitive to shear as the onset crystallization time and half crystallization time are greatly shortened even at a low shear rate, compared with neat PLLA. The synergistic effect on the crystallization rate of PLLA is likely caused by the crosslinking effect of SC crystallites on the relaxation behavior of PLLA and the filler effect of SC crystallites, which, in nature, can enhance the flow-induced crystallization. The results suggest that SC crystallites can be an attractive nucleation agent to promote the crystallization rate of PLLA especially in practical processing and the appearance of the solid crystallites in the melt can speed up the following flow induced crystallization process.