Engineering green and high-flux poly(vinylidene fluoride) membranes for membrane distillation via a facile co-casting process

A high-flux and stable poly(vinylidene fluoride) (PVDF) membrane that is also produced in a green method is particularly promising for membrane distillation (MD). In this work, a facile co-casting method was employed to fabricate porous PVDF membranes by using green solvent (PolarClean) and green casting fluids, including Acetyl tributyl citrate (ATBC) and polyethylene glycol 400 (PEG 400). During the co-casting process, ATBC or PEG was functioned as isolation layer to avoid rapid solvent/non-solvent exchange rate that could result in a dense membrane surface. The resulting top PVDF membrane surfaces were both highly porous during the phase inversion process after being cast by ATBC or PEG. In addition, the bottom surfaces were highly porous when using non-woven fabrics (NWFs) as casting supports whatever the PVDF concentrations were. It is worth mentioning that when the PVDF concentrations were below 20 wt%, the NWFs combined with PVDF membrane well that also provided a super-high mechanical strength for PVDF membranes. When the PVDF concentrations were above 25 wt%, the NWFs were detached from the PVDF membrane. Therefore, two kinds of PVDF membranes (with and without NWFs) could be produced. The optimized PVDF membranes with contact angle of above 120° showed above 99.99% and 99.9% rejection for saline water and ginseng extract during the MD process with a highest flux of ∼37 kgm⁻²h⁻¹. This work provides a green and high-flux PVDF membrane for saline water and food extract in chemical industries.