Hydrogels superabsorbent polymer

Superabsorbents. Water-sweUable polymers are used extensively in consumer articles and for industrial appUcations. Most of these polymers are cross-linked acryUc copolymers of metal salts of acryUc acid and acrylamide or other monomers such as 2-acrylamido-2-methylpropanesulfonic acid. These hydrogel forming systems can have high gel strength as measured by the shear modulus (134). Sometimes inorganic water-insoluble powder is blended with the polymer to increase gel strength (135). Patents describe processes for making cross-linked polyurethane foams which contain superabsorbent polymers (136,137). 

Another variation on the luminol CL sensor for N02 was introduced by Collins and Ross-Pehrsson [12] where a solid-phase reagent was positioned below a PMT, across which the air under test is pumped. Of the hydrogel or polymeric sorbents investigated, a Waterlock superabsorbing polymer (hydrogel)... 

Hydrogels, 13 729-759. See also Microgels Superabsorbent polymers (SAPs) AMPS polymer, 23 721 applications for, 13 747-753 biodegradable, 13 739-742 bioerodible, 9 63 conducting, 7 524 cross-linked poly (ethylene oxide),... 

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. 

The water-absorption rate of superabsorbent polymers is affected by 1) the specific surface area of the polymers 2) the capillary action and 3) the formation of fish-eyes in the polymer hydrogels. 

Nonaka, T. Yamada, K. Watanabe, T. Kurihara, S. Preparation of superabsorbent polymer hydrogels from trialkyl-4-vinylbenzyl phosphonoium chloride-acrylamide-methylenebis-acrylamide copolymer and their properties. J. Appl. Polym. Sci. 2000, 78, 1883-1884. 

Elastic Modulus. The elastic shear modulus of swollen superabsorbent polymer is commonly measured by means of oscillatory rheometry, using any of a variety of commercially available instruments (31). The sample to be analyzed is screened to the desired particle size cut such that the swollen particle size is smaller than the gap between the measuring plates. The sample is swollen in the desired liquid, usually 0.9 wt% NaCl solution or synthetic urine. Excess liquid is removed from the swollen hydrogel by blotting to minimize interparticle slippage. The hydrogel typically is placed onto the lower circular plate. An upper conical plate is positioned at the proper sample gap, which is packed with the gel. An oscillating torque is applied at a known frequency to the upper plate and the... 

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)... 

Superabsorbent polymers have also found limited utility as additives to soil to improve the water-holding ability. The hydogel absorbs the water and controls its release back into the soil as conditions become drier. Poly(ammonium acrylate) and poly(acrylamide) hydrogels have been studied for spray application to the soil and plants. The gels are prepared for spraying by adding water to provide a readily deformable polymer that will pass... 

In comparison with the absorption sheet using only a natural pulp sheet, the water absorption and preservation ability improves by the factor of several hundred % simply by exchanging only a small amount (approximately 10% by weight) of a superabsorbent polymer. In terms of eooling ability, the water-absorbed hydrogel is approximately equivalent to the same amount of water whereas the frozen hydrogel is about the same as a similar amount of ice. 

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. 

Superabsorbent polymers or superabsorbent polymer gels are mostly crosslinked polymers that have a high coneentration of anions such as carboxylic acid. These ionie groups are hydrated and a large amount of water is absorbed. The polymer then swells, forming a hydrogel. 

Manipulation of the temperature or pH, or addition of multi-valent metal ions to dilute polymer solutions are common techniques for creating hydrogels, but these fall outside of conventional superabsorbent technology. Gels of gelatin, certain natural gums, and sodium silicate are not the same as superabsorbent polymer gels. The key difference Is spontaneity. The former require assistance to gel while the latter form gel merely upon exposure to water. 

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