Superabsorbent materials, hydrogels

Oligomeric agents were prepared by condensing trimethylolpropane with ethylene and/or propylene oxides and capping with acrylic acid. These materials were subsequently crosslinked using 2,2 -azobisamidinopropane dihydrochloride, which formed superabsorbent swellable hydrogel addition polymers and were useful as components in diapers or in feminine hygiene products. 

Acrylic/methacrylic acid hydrogels exhibit extremely high swelling capacities, e.g., poly (acrylic acid) hydrogels can have water content as high as 99%, and hence are used as a superabsorbing material. The commercially important superabsorbent polymers are cross-linked polymers of partially neutralized acrylic acid or terpolymers of acrylic acid, sodium acrylate, and a cross-linker, or graft terpolymers with starch or poly(vinyl alcohol)... 

The possibility of using superabsorbent hydrogels as water managing materials for the renewal of arid and desert environments has attracted great attention [135]. These materials can reduce irrigation... 

Superporous hydrogels (SPHs) ate materials developed to demonstrate fastswelling and superabsorbent properties (Omidian et al., 2005). These were initially proposed as gastric retention devices however, SPHs may be tailor-made for other applications in pharmaceutical arxl biomedical industries (Omidian et al., 2007). The high swelling pressure of SPHs can potentially be used to trigger an alarm system upon the incursion of water and hence, can be utilized as smart hydrogels or sensors for various apphcations. 

D.C. Roe, Absorbent structures containing specific particle size distributions of superabsorbent hydrogel-forming materials mixed with inorganic powders, US Patent 5419956, assigned to The Procter Gamble Company (Cincinnati, OH), May 30,1995. 

The wraparound tape is made of a substrate sheet, such as a plastic film or nonwoven cloth, on which a superabsorbent polymer is coated. The superabsorbent polymer powder is mixed with an adhesive material, such as an organic polymer binder or a water-soluble resin, and coated onto the sheet. The sheet is then dried, fixed, and cut into strips. When the tape is in contact with water, the superabsorbent polymer particles absorb the water, swell, and become large hydrogel particles to prevent water penetration. 

The physicochemical models utilized to analyze the equilibrium swelling behavior of neutral and ionic, porous and non-porous hydrogels are reviewed. Emphasis is given to the determination of the molecular weight between crosslinks and the equilibrium swelling ratio, especially in relation to utilization of such materials in superabsorbent and controlled release technology. 

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