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 α form crystal of PLLA was highly oriented in the drawing direction in a sample cold-crystallized at Tc = 120 °C, whereas the tilt-orientation of the [200]/ [110] axes of PLLA was induced in the sample crystallized at Tc = 120 °C after preheating at Tp = 164.5–168.5 °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 μm 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 α form crystal of PLLA along the [201]/[111] axes of the β form crystal of PVDF that is induced by lattice matching of d100(PLLA) ≈ 5d201(PVDF). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1376–1389, 2008