Melt spinning of beta-phase poly(vinylidene fluoride) yarns with and without a conductive core

Journal article, 2011

When poly(vinylidene fluoride) (PVDF) is to be used as a piezoelectric material, the processing must include the formation of polar beta-phase crystallites, as well as the application of electrically conducting charge collectors, that is, electrodes. In this article, results from the melt spinning of PVDF yarns and a novel bicomponent PVDF-yarn with a conductive carbon black/polypropylene (CB/PP) core are presented. Melt spinning has been done under conditions typical for industrial large-scale fiber production. The effects on the resulting crystalline structure of varying the spinning velocity, draw rate, and draw temperature are discussed. The results show that, for maximum alpha-to-beta phase transformation, cold drawing should take place at a temperature between 70 and 90 degrees C, and both the draw ratio and the draw rate should be as high as possible. It was observed that the cold drawing necessary to form beta-phase crystallinity simultaneously leads to a decrease in the core conductivity of the bicomponent yarns. In this work, the melt spinning of bicomponent fibers with high-beta-phase PVDF in the sheath and a CB/PP core was successfully accomplished. The core material remained electrically conductive, paving the way for the use of a CB-polymer compound as inner electrode in the melt spinning of piezoelectric bicomponent fibers.