Highly drawn poly (vinylidene fluoride) with enhanced mechanical and electrical properties

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Abstract
A study has been made of the enhancement of the mechanical, piezoelectric and pyroelectric properties of polyvinylidene fluoride by orientation beyond the natural draw ratio. It was found that the best results were obtained by tensile drawing of the polymer at high temperatures. In previous studies lower temperature deformation has been a prominent feature, e.g. drawing at 80°C produces samples with a high percentage of Form I (β) crystalline material. Drawing to the limiting extensibility at high temperatures produced increased molecular alignment and considerable enhancement of properties. For example, drawing at 140°C resulted in moduli in excess of 4 GPa, and larger piezoelectric (hydrostatic) and pyroelectric coefficients, (16 pc N−1 and 45 μc m−2 K−1 respectively for 100 μm thick material). The high draw-ratio was accompanied by a stress-induced phase transition from Form II to Form I with greater than 70% of Form I being produced.