Process for making foams useful as absorbent members for catamenial pads

A process for the preparation of an absorbent polymeric foam material capable of absorbing blood and blood-based fluids, which comprises the steps of:

• A) forming a water-in-oil emulsion under from:
• 1) an oil phase comprising:
• a) from about 85 to about 98% by weight of a monomer component capable of forming a copolymer having a Tg of about 50.degree. C. or lower, the monomer component comprising:
• i) from about 45 to about 70% by weight of at least one substantially water-insoluble monofunctional monomer capable of forming an atactic amorphous polymer having a Tg of about 35.degree. C. or lower;
• ii) from about 10 to about 40% by weight of at least one substantially water-insoluble monofunctional comonomer capable of imparting toughness about equivalent to that provided by styrene;
• iii) from about 5 to about 25% by weight of a first substantially water-insoluble, polyfunctional crosslinking agent selected from the group consisting of divinylbenzenes, trivinylbenzenes, divinyltoluenes, divinylxylenes, divinylnaphthalcnes divinylalkylbenzenes, divinylphenanthrenes, divinylbiphenyls, divinyidiphenylmethanes, divinylbenzyls, divinylphenylethers, divinyidiphenylsulfides, divinylfurans, divinylsulfide, divinylsulfone, and mixtures thereof;
• and
• iv) from 0 to about 15% by weight of a second substantially water-insoluble, polyfunctional crosslinking agent selected from the group consisting of polyfunctional acrylates, methacrylates, acrylamides, methacrylamides, and mixtures thereof;
• and
• b) from about 2 to about 15% by weight of an emulsifier component which is soluble in the oil phase and which is suitable for forming a stable water-in-oil emulsion, the emulsion component comprising:
• (i) a primary emulsifier having at least about 40% by weight emulsifying components selected from diglycerol monoesters of linear unsaturated C.sub.16 -C.sub.22 fatty acids, diglycerol monoesters of branched C.sub.16 -C.sub.24 fatty acids, diglycerol monoaliphatic ethers of branched C.sub.16 -C.sub.24 alcohols, diglycerol monoaliphatic ethers of linear unsaturated C.sub.16 -C.sub.22 alcohols, diglycerol monoaliphatic ethers of linear saturated C.sub.12 -C.sub.14 alcohols, sorbitan monoesters of linear unsaturated C.sub.16 -C.sub.22 fatty acids, sorbitan monoesters of branched C.sub.16 -C.sub.24 fatty acids, sorbitan monoesters of linear saturated C.sub.10 -C.sub.14 fatty acids, and mixtures thereof, or (ii) a combination of a primary emulsifier having at least about 20% by weight of said emulsifying components and a secondary emulsifier in a weight ratio of primary to secondary emulsifier of from about 50:1 to about 1:4, said secondary emulsifier being selected from the group consisting of long chain C.sub.12 -C.sub.22 dialiphatic, short chain C.sub.1 -C.sub.4 dialiphatic quaternary ammonium salts, long chain C.sub.12 -C.sub.22 dialkoyl(alkenoyl)-2-hydroxyethyl, short chain C.sub.1 -C.sub.4 dialiphatic quaternary ammonium salts, long chain C.sub.12 -C.sub.22 dialiphatic imidazolinium quaternary ammonium salts, short chain C.sub.1 -C.sub.4 dialiphatic, long chain C.sub.12 -C.sub.22 monoaliphatic benzyl quaternary ammonium salts, and mixtures thereof;
• and
• 2) a water phase comprising an aqueous solution containing from about 0.2 to about 20% by weight of a water-soluble electrolyte;
• 3) a volume to weight ratio of water phase to oil phase in the range of from about 20:1 to about 125:1;
• and
• B) polymerizing the monomer component in the oil phase of the water-in-oil emulsion to form a polymeric foam material that is capable of acquiring and distributing blood based fluids;
• C) washing the polymeric foam material to lower the level of residual electrolytes to less than about 2%;
• D) treating the washed foam with an effective amount of a hydrophilizing surfactant;
• E) dewatering the washed foam to a moisture content of about 40% or less.