Abstract
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 been studied by X-ray diffraction, infrared spectroscopy, dynamic mechanical measurements, and tensile tests. It was found that the ductility and the crystal structure of the resultant drawn products were significantly influenced by both the initial morphologies and the drawing techniques. Solid-state coextrusion of GEL (10 wt%) films slightly below the melting point produced oriented films with only the crystalline form; those have a high chain orientation with fc=0.993, and a higher crystallinity of 55%. The chain orientation and crystallinity of such samples were significantly higher than those of the β form samples 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, respectively, were obtained by two-stage drawing of GEL films. 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 α-crystal form to the hard β-form during deformation.
