Abstract
Thin films of poly(vinylidene fluoride) have been prepared by the recently developed technique of solid state coextrusion. The films have been produced at extrusion rates of ⩾1.0 cm/min at ∼50°C below the ambient melting point (∼175°C) with a maximum extrusion draw ratio of 5.3. The films were assessed by mechanical tests, by measurements of infrared dichroism, birefringence, X-ray, density and by thermal analysis. A maximum birefringence of 0.067, the highest ever reported, and a modulus of 4.0 GPa were observed. Absolute crystallinity increased by ∼7% on drawing. Flow line studies showed that the mode for deformation changed with increasing extrusion draw ratio from shear to an extensional flow. Polarized infrared spectra and X-ray diffraction patterns showed that the crystalline α polymorphic phase converts on extrusion completely to the β phase. The α polymorph itself shows two melting peaks whereas the β polymorph exhibits three different melting peaks, indicative of crystals of different perfection.
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