The Crystallization Behavior of Poly(D-Lactic Acid)/Poly(L-Lactic Acid) Asymmetric Blends: Effect of Morphology of Stereocomplex Crystals on the Formation of Homochiral Crystals

The blends of poly(D-lactic acid) and poly(L-lactic acid) (PDLA/PLLA) produce the stereocomplex crystals (SC) with a melting temperature of similar to 250 degrees C, which exhibits higher crystallization rate and mechanical strength than PDLA or PLLA. The SC was also reported as an effective nucleator for PLA homochiral crystals (HC). In the PDLA/PLLA blends, the SC would develop at first in most of cases. However, the morphology of SC in the asymmetric blends were rarely reported, and the effect of the SC morphology on the subsequently crystallization of HC was not clear yet. In this study, the PDLA/PLLA blends with dissimilar weight ratios were prepared by three methods, i.e., electrostatic spinning, solution casting, and melted-cooling, and the SC with different morphologies were achieved. Then, the crystallization behavior of HC under the existence of SC was studied. Results indicated that the SC morphology exerted diverse effects on the formation of HC. The SC with fibrous and banded morphology produced by electrostatic spinning presented great limitation for the formation of HC. The SC with spherical morphology developed in the solution casting films enhanced the formation of HC. The SC with network structure produced in the melted-cooling specimens accelerated the crystallization rate of HC significantly. This investigation indicated that not only the content of SC, but also the morphology of SC would influence the crystallization behavior of HC, which would make a deep understanding for the crystallization behavior of PDLA/PLLA specimens.