Superabsorbent polymer
A superabsorbent polymer (SAP) (also called slush powder) is a water-absorbing hydrophilic homopolymers or copolymers[1] that can absorb and retain extremely large amounts of a liquid relative to its own mass.
[2] Water-absorbing polymers, which are classified as hydrogels when mixed,[3] absorb aqueous solutions through hydrogen bonding with water molecules.
[citation needed] The presence of valence cations in the solution impedes the polymer's ability to bond with the water molecule.
The SAP's total absorbency and swelling capacity are controlled by the type and degree of cross-linkers used to make the gel.
High cross-link density polymers exhibit lower absorbent capacity and swell, and the gel strength is firmer and can maintain particle shape even under modest pressure.
The first commercial use was in 1978 for use in feminine napkins in Japan and disposable bed liners for nursing home patients in the United States.
In the early 1960s, the United States Department of Agriculture (USDA) was conducting work on materials to improve water conservation in soils.
A wide range of grafting combinations were attempted including work with acrylic acid, acrylamide and polyvinyl alcohol (PVA).
Today's research has proved the ability of natural materials, e.g. polysaccharides and proteins, to perform super absorbent properties in pure water and saline solution (0.9%wt.)
[12] Polyacrylate/polyacrylamide copolymers were originally designed for use in conditions with high electrolyte/mineral content and a need for long term stability including numerous wet/dry cycles.
A mixture of acrylic acid, water, cross-linking agents and UV initiator chemicals are blended and placed either on a moving belt or in large tubs.
the most popular method for making the sodium polyacrylate superabsorbent polymers now used in baby diapers and other disposable hygienic articles.
The net result is that the suspension polymerization creates the primary polymer particle in the reactor rather than mechanically in post-reaction stages.
