The inexistence of epitaxial relationship between stereocomplex and α crystal of poly(lactic acid): Direct experimental evidence

In order to obtain a clear understanding to the interplay between the homogeneous crystal (α form) of PLA and its stereocomplex (SC) crystal, the crystalline behavior of PLA homopolymer under the surface drive force of SC and homopolymer fibers has been investigated in the present work. It was found that the nucleating density of the transcrystallization layer along the SC fiber was much lower than that along the homopolymer ones. Such morphologic difference between transcrystallization induced by SC and homopolymer fibers became more pronounced at higher crystallization temperature. The crystallization induction period (ti) of PLLA onto SC fiber was five times longer than that along homopolymer ones at 160 °C. However, if the blend fiber was predominantly containing α crystal, it could exhibit high nucleating capability as well as the homopolymer fibers. The results of TEM selected area electron diffraction (SAED) also revealed that the organization and orientation of α crystal were independent with the presence of SC substrate. Our results clearly indicated that there is no epitaxial relationship between PLA SC and α crystal.