Preparation of patterned flat-sheet membranes using a modified phase inversion process and advanced casting knife construction techniques

High fluxes and low fouling are practically highly desired in all membrane processes. One generic way to realize this is by introducing surface patterns on the membrane to increase the active area and the surface roughness. A new method to prepare flat-sheet patterned membranes using a patterned knife combined with a modified phase inversion process is now presented. After casting the polymer solution, the patterned knife shapes the top surface into the desired pattern. Non-solvent is sprayed immediately after the passage of the knife to rapidly solidify the polymer and preserve the pattern. To construct the patterned knife, different materials and techniques were evaluated: (1) an aluminium knife shaped by electrical discharge micromachining, (2) a gypsum knife shaped by powder-based 3D-printing, and (3) an acrylate resin, shaped by photopolymerization 3D-printing (stereolithography). As such, replacing the conventional non-solvent contact in the phase inversion via immersion by spraying already increased membrane permeance, but a significant further increase of permeance resulted from the increased surface area realized through the patterning. A minimum viscosity of the casting solution of around 7.5–10 Pa.s was required to realize well-pronounced patterns on the membrane, as screened for polyacrylonitrile and cellulose acetate, both dissolved in dimethyl sulfoxide and using water as non-solvent.