Electron beam induced modification of membranes by polymers

A method for producing a microporous membrane filter on whose surface an electron beam radiation crosslinked polymer is fixed, said method comprising the steps of:

• a) providing a microporous starting membrane having outer surfaces and pores with inner surfaces extending between the outer surfaces of the membrane and having a microporous starting membrane permeability;
• b) pretreating the microporous starting membrane with a wetting liquid selected from the group consisting of alcohols, ketones and combinations thereof;
• c) directly exchanging the wetting liquid for an impregnating solution consisting of a solvent and 0.01 to 20 weight percent of a polymer dissolved or dispersed therein to provide an impregnated membrane that has the solvent and the polymer in the pores and on the outer surfaces of the membrane, the polymer being an organic substance with an average molecular weight of at least 500 g/mol being selected from the group consisting of perfluorinated hydrocarbons, polyethylene oxide (PEO), polypropylene oxide (PPO), hydroxyethylcellulose, hydroxymethylcellulose, and mixtures thereof;
• d) removing an excess of the impregnating solution from the outer surface of the membrane;
• and
• e) irradiating the impregnated membrane with electron beam radiation using a dose in the range from 1 to 300 kGy to provide a crosslinked reaction product constituting a three-dimensional network formed of the microporous starting membrane and the polymer without any decomposition of the microporous starting membrane;
• wherein the microporous starting membrane permeability is not reduced by more than 10% by fixing the electron beam radiation crosslinked polymer thereto.

A method for producing a microporous membrane filter on whose surface an electron beam radiation crosslinked polymer is fixed, said method comprising the steps of:

• a) providing a microporous starting membrane having outer surfaces and pores with inner surfaces extending between the outer surfaces of the membrane and having a microporous starting membrane permeability,
• b) impregnating the membrane with an impregnating solution consisting essentially of a solvent and 0.01 to 20 weight percent of a polymer dissolved or dispersed therein,
• wherein the impregnating solution is free of monomers and crosslinking agents;
• thereby providing an impregnated membrane that has the solvent and the polymer in the pores and on the outer surfaces of the membrane, the polymer being an organic substance with an average molecular weight of at least 500 g/mol being selected from the group consisting of perfluorinated hydrocarbons, polyethylene oxide (PEO), polypropylene oxide (PPO), hydroxyethylcellulose, hydroxymethylcellulose, and mixtures thereof;
• and
• c) irradiating the impregnated membrane with electron beam radiation using a dose in the range from 1 to 300 kGy to provide a crosslinked reaction product constituting a three-dimensional network formed of the microporous starting membrane and the polymer without any decomposition of the microporous starting membrane;
• d) treating the crosslinked reaction product with an extractant that dissolves unconverted polymer, crosslinked polymer that is not fixed on the membrane and solvent residues from the impregnating step so that the crosslinked reaction product is free of extractable components left over from the impregnating solution;
• wherein the microporous starting membrane permeability is not reduced by more than 10% by fixing the electron beam radiation crosslinked polymer thereto.