DRAWING OF POLY(VINYLIDENE FLUORIDE) - EF FECTS OF INITIAL MORPHOLOGYAND TECHNIQUE ON THE STRUCTURE AND PROPERTIES OF DRAWN PRODUCTS

Poly(vinylidene fluoride) films with a variety of initial morphologies have been drawn by solid-state coextrusion and two-stage drawing. The resultant structure and tensile properties of drawn products have bee n studied by X-ray diffraction, infrared spectroscopy, dynamic mechani cal measurements, and tensile tests. It was found that the ductility a nd the crystal structure of the resultant drawn products were signific antly influenced by both the initial morphologies and the drawing tech niques. Solid-state coextrusion of GEL (10 wt%) films slightly below t he melting point produced oriented films with only the beta crystallin e form; those have a high chain orientation with f(c)=0.993, and a hig her crystallinity of 55%. The chain orientation and crystallinity of s uch samples were significantly higher than those of the beta form samp les usually prepared by cold-drawing of a melt-quenched film. Further, the highest achieved tensile modulus and strength at room temperature of 9.0 GPa (dynamic modulus at 35 Hz of 10 GPa) and 0.90 GPa, respect ively, were obtained by two-stage drawing of GEL alms. Such a tensile modulus corresponds to approximately 1.4 times the highest previously reported modulus value of 6.5 GPa. The fairly low ductility of PVDF is ascribed to the crystal transformation from the initial soft alpha-cr ystal form to the hard beta-form during deformation.