Direct ink writing of dehydrofluorinated Poly(Vinylidene Difluoride) for microfiltration membrane fabrication

Here, a hybrid process for the fabrication of dehydrofluorinated PVDF (dPVDF) microfiltration (MF) membranes is presented. dPVDF was fabricated through the bulk modification of PVDF using ethylenediamine. To produce inks for direct ink writing (DIW), the dPVDF was dissolved in N,N-dimethyacetamide along with a pore-forming agent, poly(vinyl pyrrolidone) (PVP) (5–30 wt%, relative to dPVDF concentration). Membranes were produced by direct ink writing of the inks into continuous films – followed by non-solvent induced phase separation (NIPS). Attenuated total reflectance – Fourier transform infrared (ATR-FTIR) and Raman spectroscopies confirmed alkene moieties within the dPVDF polymer, resulting from the dehydrofluorination process. The crystallization temperature and melting temperature for both pristine PVDF and dPVDF were similar, indicating no substantial inter-molecular cross-linking within the dPVDF polymer. The fabricated dPVDF membranes were more hydrophobic (water contact angle, WCA ≈ 115°) than the similarly fabricated PVDF membranes (WCA ≈ 99°), yet had greater equilibrium water content (EWC) and porosity (ε), which correlated to the morphology of the fabricated membranes. The dPVDF membranes with 30 wt% PVP not only demonstrated stability in a caustic environment (1 M NaOH for 90 min), but also had a pure water flux of ~4300 L m−2 h−1, within the range of commercially available PVDF membranes (~6300–8100 L m−2 h−1). Thus, with commercially relevant fluxes, increased caustic resistance, and pendant alkene groups for post-modification these DIW dehydrofluorinated membranes offer an exciting new potential for a broad range of applications.