Mechanisms of multiple types of lamellae and spherulites in poly(l -lactic acid) interacting with poly(4-vinyl phenol)

Abstract

Multiple types of crystalline morphology are present in low-molecular-weight poly(l-lactic acid) (LMw-PLLA) upon blending with poly(vinyl phenol) (PVPh) with 70/30 composition. In such a mixture, three different types of spherulite co-exist at the same crystallization temperature (Tc = 120 °C), code-named as Type-1, Type-2, and Type-3, as distinguished from their shape, birefringence, and optical signs. The PLLA molecular weights, the presence of amorphous PVPh, and Tc, etc., are factors for the formation of three uniquely different types of spherulite in PLLA. On increasing Tc from 120 to 130 °C, only hexagonal crystals (Type-1), can be observed. Spherical-shape lamellar plates at T c = 120 °C undergo transformation to stretched-lamellae plates, Tc = 130 °C, due to the increasing growth rate with increasing Tc. Low-molecular-weight poly(l-lactic acid)/poly(4-vinyl phenol) (LMw-PLLA/PVPh) (70/30) blend exhibits three different types of crystalline morphology at the same Tc. These three types of morphology can be distinguished by their shape, optical sign, and birefringence. A combination of several factors, such as PLLA molecular weights, the presence of amorphous PVPh, and the crystallization temperature, is necessary for the formation of three uniquely different types of spherulites in PLLA. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.