Water sorption isotherms and textural properties of bio-degradable starch-based super-absorbent polymers

Abstract

A series of biodegradable superabsorbent polymers (SAP) based on starch grafted withacrylic acid (AA) and crosslinked with N,N'-methylenebisacrylamide (MBIS) were obtained. Theparameters that define SAPs properties, such as starch type, amount of initiator, acrylic acid andcrosslinker concentrations, and degree of neutralization were varied according to an experimentaldesign. The swelling rate, the degree of swelling, the water sorption isotherms and the textureprofile of the new materials were determined. A new method was used to measure the swelling rate.The water sorption results were correlated using various isothermal models as the BET (Brunauer-Emmett-Teller) and GAB (Guggenheim-Andersson-DeBoer) models.Hydrogels obtained from regular cornstarch presented better absorption capacities than thosefrom waxy cornstarch. Maximum swelling was observed for 70% neutralization of carboxylic acidgroups. More rigid SAPs presented lower swelling rates, but not necessarily lower swelling degrees.