Oriented crystallization of poly(L-lactic acid) in uniaxially oriented blends with poly(vinylidene fluoride)

This article describes the oriented crystallization of poly(L-lactic acid) (PLLA) in uniaxially oriented blends with poly(vinylidene fluoride) (PVDF). Uniaxially drawn films of PLLA/PVDF blend with fixed ends were heat-treated in two ways to crystallize PLLA in oriented blend films. The crystal orientation of PLLA depended upon the heat-treatment process. The crystal c-axis of the alpha form crystal of PLLA was highly oriented in the drawing direction in a sample cold-crystallized at T-c = 120 degrees C, whereas the tilt-orientation of the [200]/[110] axes of PLLA was induced in the sample crystallized at T-c = 120 degrees C after preheating at T-p = 164.5-168.5 degrees C. Detailed analysis of the wide-angle X-ray diffraction (WAXD) indicated that the [020]/[310] crystal axes were oriented parallel to the drawing direction, which causes the tilt-orientation of the [200]/[110] axes and other crystal axes. Scanning electron microscopy (SEM) suggested that oriented crystallization occurs in the stretched domains of PLLA with diameters of 0.5-2.0 mu m in the uniaxially drawn films of PVDF/PLLA = 90/10 blend. Although the mechanism for the oriented crystallization of PLLA was not clear, a possibility was heteroepitaxy of the [200]/[110] axes of the alpha form crystal of PLLA along the [201]/[111] axes of the beta form crystal of PVDF that is induced by lattice matching of d(100)(PLLA) approximate to 5d(201)(PVDF). (C) 2008 Wiley Periodicals, Inc.