Superabsorbent polymer

Superabsorbent polymers (SAP) are free radical, cross-linked polymers able to absorb water at a multiple of several times their own mass, forming a gel. Classified as a hydrogels, these polymers absorb aqueous solutions through hydrogen bonding with water. SAPs ability to absorb water is a factor of the ionic concentration of an aqueous solution. In deionized and distilled water, SAP may absorb 500 times its weight, but when put into a 0.9% saline solution, the absorbency drops to maybe 50 times weight. The presence valent cations in solution will impede the polymers ability to bond with the water molecule.

Superabsorbent polymers are most commonly made from the polymerization acrylic acid blended with sodium hydroxide in the presents of an intiator to form a sodium salt polymer of polyacrylic acid. This polymer is the most common type of SAP made. Other materials can be used to make a superabsorbent polymer form compounds such as, polyacrylamide copolymer, ethylene maleic anhydride copolymer, cross-linked carboxy-methyl-cellulose, polyvynyl alcohol copolymers, cross-linked polyethylene oxide, and starch grafted copolymer to name a few.

Superabsorbent polymers are made using one of two primary methods; suspension polymerization or solution polymerization. Solution based polymerization is the most common process used today to made SAP. This process is efficient and generally has a lower cost base. However, the suspension process offers a higher degree of control and product engineering during polymerization. This is because the primary polymer particle is formed in the reaction rather than outside it as with the solution process.

The total absorbency and swelling capacity are controlled by the type and degree of cross-linking to the polymer. Low density cross-linked SAPs have higher absorbent capacities and swell to a larger degree. These products also have a softer and more cohesive type gel formation. High cross-link density polymers exhibit lower absorbent capacity and swell. The gel strength is firmer and can maintain particle shape even under modest pressure.

The largest use of superabsorbent polymers is in personal disposable hygiene products, such as baby diapers, adult protective underwear and feminine napkins. (SAPs are not used in tampon as some have reported) They are also used for blocking water ingress in underground cable, horticultural water retention agents, control of spill and waste fluid (aqueous), artificial snow for motion picture and stage production. The first commercial use was in 1978 for use in feminine napkins in Japan.

Copolymer Chemistry

Polyacrylate/polyacrylamide copolymers originally designed for use in conditions with high electrolyte/mineral content and a need for long term stability including numerous wet/dry cycles. Uses include agricultural and horticultural. With the added strength of the acrylamide monomer, used as medical spill control, wire & cable waterblocking

Solution Polymers

Offers the absorbency of a granular polymer supplied in solution form. Solutions and can be diluted with water prior to application. Can coat most substrates or used to saturated. After drying at a specific temperature for a specific time, the result is a coated substrate with superabsorbent functionality. For example, this chemistry can be applied directly onto wires & cables, though it is especially optimized for use on components such as rolled goods or sheeted substrates.

Uses

• Wire & Cable Waterblocking
• Filtration Applications
• Spill Control
• Hot & Cold Therapy Packs
• Composites & Laminates
• Medical waste solidification
• Mortuary pads
• Motionless waterbeds
• Candles
• Fragrance carrier
• Wound dressings
• Fire protection
• Surgical pads
• Water retention for supplying water to plants

See also

• Sodium polyacrylate.
• The use of SAP in diapers.

External links

• video of super absorbent polymer in action creating "Instant Snow".