Benjamin Glauß

Spinnability and Characteristics of Polyvinylidene Fluoride (PVDF)-based Bicomponent Fibers with a Carbon Nanotube (CNT) Modified Polypropylene Core for Piezoelectric Applications

This research explains the melt spinning of bicomponent fibers, consisting of a conductive polypropylene (PP) core and a piezoelectric sheath (polyvinylidene fluoride). Previously analyzed piezoelectric capabilities of polyvinylidene fluoride (PVDF) are to be exploited in sensor filaments. The PP compound contains a 10 wt % carbon nanotubes (CNTs) and 2 wt % sodium stearate (NaSt). The sodium stearate is added to lower the viscosity of the melt. The compound constitutes the fiber core that is conductive due to a percolation CNT network. The PVDF sheath’s piezoelectric effect is based on the formation of an all-trans conformation β phase, caused by draw-winding of the fibers. The core and sheath materials, as well as the bicomponent fibers, are characterized through different analytical methods. These include wide-angle X-ray diffraction (WAXD) to analyze crucial parameters for the development of a crystalline β phase. The distribution of CNTs in the polymer matrix, which affects the conductivity of the core, was investigated by transmission electron microscopy (TEM). Thermal characterization is carried out by conventional differential scanning calorimetry (DSC). Optical microscopy is used to determine the fibers’ diameter regularity (core and sheath). The materials’ viscosity is determined by rheometry. Eventually, an LCR tester is used to determine the core’s specific resistance.

Poling Effects in Melt-Spun PVDF Bicomponent Fibres

This research shows the successful functionalisation of bicomponent fibres, consisting of a conductive polypropylene (PP) core, doped with carbon nanotubes (CNT) and a piezoelectric sheath (polyvinylidene fluoride, PVDF) by draw winding and poling. These steps lead to the usability of the PVDF’s piezoelectric capabilities. The PP/CNT constitutes the fibre core that is conductive due to a percolation CNT network. The PVDF sheath’s piezoelectric effect is based on the formation of β phase crystals (all-trans conformation), caused by draw-winding of the fibres. This β phase eventually has to be poled for the uniform alignment of polymer chains. The material’s behaviour in high electric field is analysed recording the poling voltage during the poling process. The outcome is hysteresis curves for different β phase contents, which verify a successful material poling.