Robust Surface-Engineered Tape-Cast and Extrusion Methods to Fabricate Electrically-Conductive Poly(vinylidene...

We developed a poly(vinylidene fluoride)/carbon nanotube (PVDF-MWCNT) filament as a feed for printing of electrically-conductive and corrosion-resistant functional material by fused filament fabrication (FFF). Using an environment-friendly procedure to fabricate PVDF-MWCNT filament, we achieved the best reported electrical conductivity of printable PVDF-MWCNT filament of 28.5 S cm^-1 (90 wt% PVDF and 10 wt% CNT). The PVDF-MWCNT filaments are chemically stable in acid, base, and salt solution, with no significant changes in electrical conductivity and mass of the filaments. Our processing method is robust and allow a uniform mixture of PVDF and CNT with a wide range of CNT percentage up to 99.9%. We demonstrated the printing of PVDF-MWCNT filaments to create 3D shapes; printed using a low-cost commercial consumer-grade FFF 3D printer. We found many adjustments of printer parameters are needed to print filament with CNT content >10 wt%, but easier printing for CNT content ≤10 wt%. Since this was due to printer limitation, we believed that PVDF-MWCNT with higher CNT percentage (to a certain limit) and larger electrical conductivity could be printed with a custom-built printer (for example stronger motor). PVDF-MWCNT filament shows higher electrical conductivity (28.5 S cm^-1) than compressed composite (8.8 S cm^-1) of the same 10 wt% of CNT, due to more alignment of CNT in the longitudinal direction of the extruded filament. Printable PVDF-MWCNT-Fe₂O₃ (with a functional additive of Fe₂O₃) showed higher electrical conductivity in the longitudinal direction at the filament core (42 S cm^-1) compared to that in the longitudinal direction at the filament shell (0.43 S cm^-1) for sample with composition of 60 wt% PVDF, 20 wt% CNT, and 20 wt% Fe₂O₃, due to extrusion skin effect with segregation of electrically insulating Fe₂O₃ at the shell surface of PVDF-MWCNT-Fe₂O₃.