Classification of superabsorbent polymers

SAPs can be classified into four groups on the basis of the presence or absence of electrical charge located in the cross-linked chains. 

Amphoteric electrolyte containing both acidic and basic groups. 

Zwitterionic containing both anionic and cationic groups in each structural repeating unit, such as polybetaines. 

SAPs are also classified based on the type of monomeric unit used in their chemical structure. Most conventional SAPs fall into one of the following categories. 

SAPs can also be divided into synthetic and natural types, with the latter being further divided into two main groups those based on polysaccharides and those based on polypeptides. Natural SAPs are usually prepared by the addition of some synthetic parts to the original substrates, for example, graft copolymerization of vinyl monomers on polysaccharides. Because of their low price and high performance, synthetic SAPs are widely used in many healthcare and hygiene products, and the term superabsorbent polymers usually implies the most conventional type of SAP, that is, an anionic copolymeric network based on partially neutralized AA or acrylamide. 

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