Kynar720

Two commercially available poly (vinylidene fluoride) (PVDF) grades were applied, namely Solef1006 (Solvay, Lyon, France, PVDF1) with a melt flow index of 40 g/10 min (230 °C, 2.16 kg) and Kynar720 (Arkema, Colombes Cedex, France, PVDF2) with a melt flow index of 5–29 g/10 min (230 °C, 5.0 kg). Rheological measurements were performed on pure PVDF materials whereby higher levels of viscosity (see Figure 1) and elasticity (see Figures S1 and S3) were found for PVDF2 compared to PVDF1.
As electrically conductive fillers, mixtures of branched multi-walled carbon nanotubes (b-MWCNTs) and carbon black (CB) were chosen. The b-MWCNT “CNS flakes” (Applied NanoStructured Solutions LLC, Baltimore, MD, USA) have a diameter of 14 ± 4 nm and length of ≈70 µm (aspect ratio ≈5000) [38 (link)] and are coated with 3 wt % poly (ethylene) glycol. The CB is a highly structured type of the grade Ketjenblack^® EC600JD (Akzonobel, Cologne, Germany) with a surface area of 1200 m²/g and a primary particle size d₅₀ of 34 nm (according to the supplier). Scanning electron microscopy images of both fillers are shown in Kunz et al. [26 (link)].

The materials used in this study were PVDF (Kynar 720, Arkema, Colombes, France) and PAR (Vectra A950, Celanese, Irving, TX, USA). The PVDF/PAR island-in-a-sea fibers were prepared by melt conjugate spinning at 270 °C as shown as Figure 1. The conjugate spinning conditions are displayed in Table 1. PVDF and PAR were used as a sea component and the island component, respectively, in a weight ratio of 5:5. In this spinning system, two connected extruders for two polymers and a conjugate spinning nozzle with many sub-holes were used. The conjugated spun fibers were wound at a speed of 650 m/min. The diameter of the conjugated fiber and the PAR component in the fiber were 39 and 4.2 $\mathsf{\mu }\mathrm{m}$ , respectively.