These absorbent polymeric foam materials comprise a hydrophilic, flexible, nonionic polymeric foam structure of interconnected open-cells that provides a specific surface area per foam volume. The foam structure has incorporated therein a toxicologically acceptable, hygroscopic, hydrated salt. The chemistry is primarily 2-Ethylhexyl acrylate and divinyl benzene with calcium chloride in the dense layer to maintain collapsed state.
This relatively thin, collapsed polymeric foam materials is obtained by polymerizing a specific type of water-in-oil emulsion, commonly known as High Internal Phase Emulsions or "HIPE". The oil phase of these HIPE emulsions comprises of a monomer component having: (a) a monofunctional glassy monomer; (b) a monofunctional rubbery comonomer; (c) a polyfunctional crosslinking agent component. The oil phase further comprises of emulsifier component that is soluble and will provide a stable emulsion for polymerization. The water or "internal" phase of these HIPE emulsions comprises an aqueous solution containing a water-soluble electrolyte. The weight ratio of the water phase to the oil phase in these HIPE emulsions is not know but should be around 50:1.The polymerized foam is subsequently dewatered to provide the collapsed foam material.
An important aspect of the process is to carry out the emulsion formation and polymerization steps in a manner such that coalescence of the relatively small water droplets formed in the HIPE emulsion is reduced. This leads to a number average cell size in the resulting polymeric foam material of about 50 microns or less. It is a key mechanism behind consistent formation of this material. This reduction in coalescence can be consistently achieved or by the use of certain emulsifier systems either by the use of lower temperatures during polymerization (curing). Stay tuned for next part.