Microscopic lamellar assembly and birefringence patterns in poly(1,6-hexamethylene adipate) packed with or without amorphous poly(vinyl methyl ether)

Lamellae arrangements by melt crystallization at different crystallization temperatures (38-48 C) of poly(1,6-hexamethylene adipate) (PHA) and its blend with 20 wt % poly(vinyl methyl ether) (PVME) under thin film state were studied by using polarized-light optical microscopy, atomic force microscopy, and wide-angle X-ray diffraction. Depending on T_c, three types of spherulitic morphologies (ringless, irregular ring-banded, and petal-like) are observed in the blend, with a sharp and clear optical birefringence reversion being observed in PVME/PHA 20/80 blend within 1 C difference. Mechanisms and lamellar assembly responsible for such birefringence reversion within 1 C difference were probed. Neat PHA only forms positive-birefringence spherulites at all T_c's. More abundant edge-on lamellae effected by the amorphous PVME on PHA crystals led to such birefringence diversity in the PVME/PHA blend, which was assessed to be one of the main factors contributing to the alteration and diversification of the signs of spherulites in PVME/PHA 20/80 blend.