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

Abstract

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 (stereo-lithography). As such, replacing the conventional nonsolvent 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.

Harvesting microalgae using vibrating, negatively charged, patterned polysulfone membranes

“…When sPSf concentration reached 25w%, the viscosity of the casting solution increased, leading to a higher fidelity (i.e. the values of H and B in the final membrane are closer to those of the casting knife) [22]. Similar phenomena were also found in previous studies [28].…”

“…Flat membranes prepared through phase inversion by spraying have been reported to show higher fluxes than when prepared via conventional phase inversion through direct non-solvent immersion. Still, the patterned membranes showed higher membrane fluxes, according to a previous study [22]. The surface and cross-sectional morphologies of the membranes are shown in Fig.…”

Harvesting microalgal biomass using negatively charged polysulfone patterned membranes: Influence of pattern shapes and mechanism of fouling mitigation

“…In addition to the hydrophilicity and surface charge modifications, surface patterning is considered an emerging method to alleviate fouling due to the unique hydrodynamic flow behavior near the membrane surface and the extended active area (Ilyas et al, 2020;Jung and Ahn, 2019;Marbelia et al, 2020;Zhao et al, 2020b).…”

“…3-D printing and etching) and chemical modification (Heinz et al, 2018), which are always limited by equipment/mold cost, complex parameter control, compressed porosity and/or low pattern fidelity (Ma et al, 2015;Marbelia et al, 2020). A recently reported one-step method, phase inversion (Hołda and Vankelecom, 2015) by spraying using corrugated casting knives, may solve these problems (Marbelia et al, 2020). The polymer solution is cast using a modified patterned knife, and non-solvent is simultaneously sprayed on the cast film to rapidly solidify the surface pattern.…”

Development of a New Polymer Membrane: Polyvinylidene fluoride/Polyetherimide Blend Membrane

“…However, the most important determinant parameter is the time between casting and immersion in the coagulation bath because PEI can only migrate in the solution phase. This time can be modified, shortened or extended as needed, on flat sheet membrane casting process [27], [28].…”