Solef 6010

PVDF HF membranes were prepared by the dry/wet spinning technique described elsewhere [25 (link),26 (link),27 (link)]. The polymeric dope was prepared by dissolving poly(vinylidene fluoride) Solef® 6010 (kindly provided by Solvay Advanced Polymers, Bollate, Italy) 25 wt.% in dimethyl formamide (DMF) (Carlo Erba Reagenti, Italy). Poly-vinyl pyrrolidone Luviskol K-17 (PVP K-17, Mw = 12 kg/mol) was purchased from BASF and used as pore forming additive, in concentration of 35 wt.%. PVP was desiccated at 50 °C under vacuum overnight before use. Different fibers types were produced by varying the bore fluid composition and flow rate. All the other spinning parameters were kept constant. The detailed conditions of fiber spinning are resumed in Table 1.
The produced PVDF hollow fibers were kept in frequently refreshed water bath for one day, to remove residual solvent and ensure complete coagulation. Afterwards, they were treated with sodium hypochlorite 4000 ppm, buffered to pH 7, in order to leach out PVP from membrane pores and increase permeability. Fibers were soaked in a glycerol/water solution (30 wt.%), in order to avoid collapse of their porous structure, before the final drying.

Polyvinylidenefluoride (PVDF) was Solef^®6010 supplied by Solvay Specialty Polymers (Milan, Italy). It is a white powder with a density of 1.78 gr/m³ and a melting temperature point between 165 and 177 °C. PVDF was chosen because it is an inert material suitable for use in contact with food products. Dimethylformammide (DMF), supplied by Sigma Aldrich (Milan, Italy), was used as a solvent for the solution. Polyvinilpyrrolidone (PVP, Luviskol K17, MW = 12 kg/mol) was supplied by BASF (Ludwigshafen, Germany). Glycerol was supplied by Carlo Erba Reagents (Milan, Italy).

Solef 6010 (SOLVAY, Brussels, Belgium) was used as the PVDF resin [18 (link),24 ]. AEROSIL-R972 (NIPPON AEROSIL, Tokyo, Japan) was the hydrophobic silica, and functioned as a pore-forming agent. The PVDF polymer was diluted using Di (2-ethylhexyl) phthalate (DOP) and dibutyl phthalate (DBP). Following fabrication, CH₂Cl₂, EtOH and NaOH were used to wash the membrane. The membrane porosity was determined using 1-Butanol., NaCl was used as a model electrolyte in the feed solution. Sodium dodecyl sulfate (SDS) was used as a model surface-active solute. All of these chemicals were purchased from FUJIFILM Wako Pure Chemical Corporation, Osaka, Japan. The fluoropolymer FS-392B (Fluoro Technology Co. Ltd., Aichi, Japan), was used as the hydrophobic agent [25 ,26 ].

PVDF powders Solef 6010, Solef 1015, and Solef 6020 were kindly donated by Solvay Specialty Polymers (Bollate, Italy). N-methyl-2-pyrrolidone (NMP, 99%) was provided by Panreac (Inca, Spain). Non-woven Hollytex 34 GR was provided by STEM Company (Teijin Aramid, Arnhem, The Netherlands). Distilled water was used as a non-solvent in the coagulation bath.