Superabsorbent Polymers

Abstract

IntroductionSuperabsorbent polymers are very high molecular mass, cross-linked Polyelectrolytes (qv) that can absorb or imbibe more than ten times their mass of water or aqueous solutions. In order to absorb this large quantity of aqueous fluid, the polymers must be only slightly cross-linked so that the polymer chains can adopt widely spaced configurations. And in order to remain largely insoluble, while at the same time being highly expanded, the polymer chains must have very high molecular mass so that the small number of cross-links connect together all the chains. Cross-linked polyelectrolytes absorb more aqueous liquid than do neutral polymers as a result of the added osmotic, swelling pressure of the counterions that balance the high electric charge of the ionized functional groups spaced along the polymer chains (see POLYELECTROLYTES).Although any high molecular mass, cross-linked polyelectrolyte can function as a superabsorbent polymer, the commercially available superabsorbent polymers are alkali metal salts of poly(acrylic acid) cross-linked with multifunctional cross-linkers (see ACRYLIC (AND METHACRYLIC) ACID POLYMERS). Most often the cross-links are formed from comonomers that are incorporated into the polymer during the free-radical-initiated addition polymerization. Common cross-linkers are di-and tri-acrylates or methacrylates. The polymer chains can also be crosslinked after the main polymer chains have been formed. In this case, the crosslinker is multifunctional with groups that can react with the carboxylic acid or carboxylate groups present along the polymer chains. Examples of this type of cross-linker are polyols, polyepoxides, polyamines, and the like. Most commonly, the polymers are made by means of free-radical-initiated polymerization of an aqueous solution of the monomers, followed by drying the hydrogel that is formed and grinding the dry polymer to a granular powder.The principal use of superabsorbent polymers is as a liquid absorbent in disposable hygiene products, which include baby diapers, feminine hygiene products, and adult incontinence products. Smaller volume uses include liquid absorbent pads for packaged meats and water-blocking tapes and coatings for electrical and telecommunication cables.

Water Absorbing Plantation Clay for Vertical Greenery System

“…The hydrophilic functional chains in superabsorbent polymer can hold a large amount of water and swell. The cross-linked chains in superabsorbent polymers tends to maintain their physical dimensional structure [15]. The postivie effect of superabsorbent polymer application as soil additives for the retention of water in soil are consistent with [8][9][10]16] However, further increment of cement content after 1.5 wt% led to decreasing water absorbing properties.…”

Radiation synthesis of hydrogels to enhance sandy soils water retention and increase plant performance

“…The use of PAAm/PAAcK hydrogel at a rate of 6 g/m 3 increases the time to wilting of corn by 50% in reference to the wilting time of control. Meanwhile, the time to wilting for corn plants planted in sandy soil treated with PAAm/PAAcK hydrogel at a rate of 15 g/m 3 increases by almost 65% referred to the wilting time of control. The magnitude of the plant wilting response may be due to the fact that, as the gel rate increases, the amount of absorbed water increases, soil water retention improves, and the available water for plant increases, resulting in delaying the wilting of the corn plant.…”

“…They can absorb large amounts of water many times their own weights, resulting in drastically increased volumes. Some of them are currently commercialized and used in various fields such as industry, 1-2 medicine, 3 and other advanced technologies, 4 -7 where water absorbency and water retention are important.…”

Proposed Cross-Linking Model for Carboxymethyl Cellulose /Starch Superabsorbent Polymer Blend

“…In addition to modifying the swelling and mechanical properties, the cross-linker affects the amount of soluble polymer found during the polymerization. Efficiency of crosslinking will also depend on steric hindrance and reduced mobility at the site of pendant double bonds, the tendency of a given crosslinker to undergo intermolecular addition reactions, and the solubility of the cross-linker in the monomer mixture [8].…”