JP 10337456 A discloses a polyacrylonitrile-based precision filter membrane having a pore size in the range of from 0.01 to 1 μm. The membrane is produced from a solution comprising 2-50 wt % (preferably 5-35 wt %, more preferably 10-25 wt %) of an acrylonitrile homo- or copolymer of at least 70 wt % acrylonitrile with ≤30 wt. % of one or more vinyl compounds copolymerizable with acrylonitrile in a mixed solvent comprising two or more organic solvents and 1-40 wt % (preferably 1-30 wt %) polyvinylpyrrolidone having a weight average molecular weight in the range of from 1,000 Da to 1,300,000 Da (preferably 2,900 Da to 110,000 Da). The mixed solvent comprises γ-butyrolactone or ethylene carbonate. Hollow fiber membranes are produced by spinning the solution into a coagulation bath having a temperature of from −30° C. to 90° C. (preferably 0° C.-90° C., more preferably 0° C.-80° C.).
Working Example 1 of JP 10337456 A describes the production of a hollow fiber membrane from a spinning solution comprising 16 wt % of a copolymer of 91.5 wt % acrylonitrile, 8.0 wt % methyl acrylate and 0.5 wt % sodium methallyl sulfonate; and 20 wt % PVP having a weight average molecular weight of 9,000 Da (BASF K17); in 48 wt % N-methyl-2-pyrrolidone (NMP) and 16 wt % γ-butyrolactone. The solution is spun at 80° C. through a double-orifice spinneret (0.5 mm-0.7 mm-1.3 mm) into a coagulation bath comprising water at 80° C., using a center fluid consisting of 90 wt % NMP and 10 wt % water. The air gap between nozzle and coagulation bath is 20 mm, the atmosphere in the spinning shaft surrounding the nozzle has a temperature of 60° C. and 100% humidity. Spinning velocity is 10 m/min. Average pore size of the membrane obtained is 0.12 μm. In Comparative Example 1, the procedure is repeated using only NMP as solvent, yielding a hollow fiber membrane having an average pore size of 0.0089 μm.
EP 0 923 984 A1 discloses a polyacrylonitrile-based hollow fiber membrane having a sponge structure. Pore sizes of the membrane continuously decrease from the center of the membrane wall towards both surfaces of the membrane, and the pore size on the outer surface of the membrane is different from that on the inner surface. The membrane is produced from a solution comprising 5 to 35 wt % of an acrylonitrile-based polymer, a solvent mixture of 2 to 99.9 wt % propylene carbonate and at least one other organic solvent capable of dissolving the acrylonitrile-based polymer, and 1 to 40 wt % of a specific additive selected from water, salts, alcohols, ketones, glycols, glycerol, and polyvinylpyrrolidone having a weight average molecular weight of from 1 to 2,800 kDa.
Working Example 1 of EP 0 923 984 A1 details the production of a hollow fiber membrane from a solution of 18.5 wt % of a copolymer of 91.5 wt % acrylonitrile, 8.0 wt % methyl acrylate and 0.5 wt % sodium methallyl sulfonate; and 21 wt % poly-ethylene glycol having a weight average molecular weight of 600 Da (PEG 600); in a mixture of 9.15 wt % propylene carbonate and 51.85 wt % of dimethyl sulfoxide. The membrane had an inner diameter of 760 μm and an outer diameter of 1340 μm, an average pore size on the outer surface of 0.02 μm and an average pore size on the inner surface of 0.08 μm. Its water permeability was 96·10−4 cm3/(cm2·bar·sec).
KR 415342 B1 discloses a method for manufacturing a polyacrylonitrile porous hollow fiber membrane which is used as an ultrafiltration membrane. The process uses a polymer solution comprising 12-25 wt % polyacrylonitrile; 3-15 wt % of a first additive comprising polyvinylpyrrolidone, polyvinyl alcohol or a mixture thereof; 10-40 wt % 1-butoxyethanol as second additive; and a solvent selected from the group consisting of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and mixtures thereof. The examples use DMF solutions comprising 18-22 wt % polyacrylonitrile having a weight average molecular weight of 150 kDa; and 5% PVP having a weight average molecular weight of 10 kDa. The membranes obtained comprise 5 or 7 different zones, two of them having a finger structure with macrovoids.
KR 20010106681 A discloses a method for preparing a polyacrylonitrile porous flat sheet membrane having a sponge structure without macrovoids. The process uses a polymer solution comprising 10 wt % polyacrylonitrile and 5 wt % polyvinylpyrrolidone in dimethylsulfoxide. The solutions are spread onto a glass plate and dipped into a coagulation bath comprising 70 wt % dimethylsulfoxide, 20 wt % water and 10 wt % polyvinylpyrrolidone. Different polyvinylpyrrolidones with weight average molecular weights of 10 kDa, 55 kDa, and 1,300 kDa, respectively, are used in the examples. Membranes showing a sponge structure without macrovoids were only obtained with polyvinylpyrrolidone having a weight average molecular weight of 10 kDa.
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