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The super absorbent polymer (SAP) also called powder snow, it is polymer that can absorb and retain extremely large amounts of a liquid relative to its own mass. The water absorbent polymers, which are classified as hydrogels when crosslinked absorb aqueous solutions through hydrogen bridge bonds with water molecules. The ability of a super absorbent polymer to absorb water is a factor of the ionic concentration of the aqueous solution. In deionized, distilled water, a super absorbent polymer may absorb 500 times its weight (30 to 60 times its own volume) and can be up to 99.9% of liquid, but when placed in a saline solution 0.9%, low absorption capacity for maybe 50 times its weight. The presence of cations in the solution prevents the ability of the polymer to the link with the water molecule.
The total absorbency and swelling capacity are controlled by the type and amount of cross linking agents used to make the gel. Crosslinking the super absorbent polymer low density generally have a greater absorbent capacity and swell to a greater degree. These types of super absorbent polymers also have a softer gel formation and sticky. The polymers with high densities of crosslinking exhibit lower absorbent capacity and swell, but the gel strength is stronger and can maintain the shape of the particles, even under moderate pressure.
The increased use of super absorbent polymer is found in disposable hygiene products such as baby diapers, adult protective underwear and sanitary napkins. The super absorbent polymer using tampons in 1980 due to concerns about an association with toxic shock syndrome (potentially fatal disease caused by a bacterial toxin) was suspended. The super absorbent polymer is also used to block the penetration of water into power lines or underground communications, horticultural water retention agents, spill control and waste aqueous fluid, and artificial snow production. The first commercial use was in 1978 for use in Japan feminine napkins and disposable bags bed for patients of nursing homes.
Until the 1980s, the water absorbing materials were cellulose or fiber based products. The options were tissue paper, cotton, sponge and fluff pulp. The water absorbing capacity of such materials is only up to 11 times its weight, but most is lost under moderate pressure.
In early 1960, the United States Department of Agriculture (USDA) was conducting work on materials to improve water conservation in soils. They developed a based on acrylonitrile graft molecules in the backbone of starch molecules (ie, starch-grafted) resin. The hydrolyzed product of the hydrolysis of this starch-acrylonitrile copolymer gave a water absorption greater than 400 times its weight. In addition, the gel did not release liquid water in the way that if they did absorbent fiber based.
The polymer became known as 'super slurper' (superabsorbent). The USDA give the technical knowledge to various US companies for further development of the basic technology. A wide range of combinations were tried including working with acrylic acid, acrylamide, and polyvinyl alcohol (PVA).
The acrylate-acrylamide copolymers were originally designed for use under high electrolyte / mineral content and the need for long-term stability including many wet / dry cycles. It is used in agriculture and horticulture. With the further addition of acrylamide monomer is used as a control spill physician and water blocking cables.
The sodium polyacrylate
As mentioned, one of the most commonly used superabsorbent polymers is sodium polyacrylate. It is a polymer formed from monomers —CH2CH(CO2Na)—. It is a white odorless powder. You can increase your volume to a thousand times if you add distilled water. Due to its qualities is used in diapers, sanitary napkins or chemical processes requiring water absorption.
The capacity to absorb large quantities of water because in its molecular structure there sodium carboxylate groups hanging off the main chain of the compound composition. These groups leaving free negative ions carboxyl when in contact with water emit sodium. The negative ions are repelled, stretching the backbone and causing increased volume. For the compound to be stable again and neutral, the ions capture water molecules. This powder by adding water can see how each of the grains is absorbed, and gathering up will form a kind of crystalline gel. Since this compound has high molecular weight, rather than dissolved, it is gelled. This compound also has the unique feature to resemble snow viewed with the naked eye, so it serves to create fake snow.
The different superabsorbent polymers can be used for a variety of applications, including the controlled release of insecticides and herbicides, diapers and incontinence garments, filtration, as additives thickeners and scavengers, fireproof gel, fragrance carrier, toys (that grow in water), packs or packages of therapy of heat and cold, solidification of medical waste, water beds non-moving, spill control, surgical pads, potting soil, waste stabilization and environmental remediation, water retention for supplying water to the plants, water blocking cable, wound dressings, removal of water from aviation fuel, removal of moisture in packaging, artificial snow, etc.