Asymmetric semipermeable membrane for the treatment of biological fluids

A process for the preparation of an asymmetric, semipermeable membrane comprising a support layer and at least one dense, mesoporous or microporous surface layer defining a separating layer, comprising the steps of:

• preparing a solution containing at least one hydrophobic polymer;
• at least one water-insoluble copolymer, the copolymer comprising acrylonitrile and at least one sulphonic monomer, the polymer and copolymer present in respective proportions such that the dimensional variation of the membrane thus produced does not exceed +3% when it changes from the dry state to the wet state at 40.degree. C.;
• at least one organic solvent for the hydrophobic polymer and the copolymer having a boiling temperature higher than the processing temperature of the solution;
• and at least one nonsolvent for the hydrophobic polymer miscible with the organic solvent;
• wherein the hydrophobic polymer, copolymer, organic solvent and nonsolvent are present in said solution in respective amounts such that the thus obtained solution is thermodynamically unstable and cloudy, but macroscopically homogeneous, does not give rise to demixing at the processing temperature of the solution, and where a lowering of the temperature of the solution would spontaneously cause gelification of the solution;
• extruding the thus obtained solution,
• coagulating the thus extruded solution for a period of time sufficient to produce a solidified membrane product;
• and
• washing the thus obtained membrane.

A process for the preparation of an asymmetric, semipermeable membrane comprising a support layer and at least one dense, mesoporous or microporous surface layer defining a separating layer comprising the steps of:

• preparing a first solution comprising at least one hydrophobic polymer, and at least one organic solvent for the hydrophobic polymer the solvent having a boiling temperature higher than the processing temperature of the first solution;
• preparing a second solution comprising at least one water-insoluble copolymer based on acrylonitrile and at least one sulphonic monomer at least one organic solvent for the copolymer and for the hydrophobic polymer having a boiling temperature highest than the processing temperature of the solution, wherein at least one of the first and the second solutions further comprises at least one nonsolvent for the hydrophobic polymer miscible with both the organic solvent for the hydrophobic polymer and the organic solvent for the copolymer, and wherein the organic solvent in the first solution is a solvent for the copolymer;
• mixing the first solution and the second solution wherein the copolymer and the hydrophobic polymer are present in the thus mixed solution in respective proportions that the dimensional variation of the membrane ultimately produced does not exceed +3% when the membrane changes from the dry state to the wet state at 40.degree. C.;
• and wherein the hydrophobic polymer, the copolymer, the solvent and the nonsolvent are present in the thus mixed solution in respective amounts such that the solution is thermodynamically unstable and cloudy, but macroscopically homogeneous, does not give rise to demixing at the processing temperature of the solution. and where a lowering of the solution temperature would spontaneously cause gelification of the solution;
• extruding the thus obtained solution;
• coagulating the thus extruded solution for a period of time sufficient to produce a solidified membrane product;
• and
• washing the thus obtained membrane.