Novel itaconic acid-based superabsorbent polymer with improved gel strength and salt resistance using 2-acrylamido-2-methyl-1-propanesulfonic acid

The synthesis of novel superabsorbent polymers (SAPs) based on itaconic acid (IA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) is described for application in personal hygiene products such as disposable diapers. The AMPS is introduced to improve the low absorption performance of the existing IA-based SAPs. The salt-resistant properties of AMPS are shown to improve the absorption performance of SAP with respect to aqueous salt solutions. Further, the high ionization constant of the sulfonic acid group of AMPS contributes to the increase of the centrifugation retention capacity (CRC) of the SAP. Meanwhile, the amide group of AMPS improves the gel strength of the SAP by forming hydrogen bonds between the polymer chains. This increase in gel strength is demonstrated by the enhanced absorbency under load (AUL) and rheological analysis. The degree of neutralization affect the absorption properties of SAP, and the SAP exhibits maximum CRC and AUL of 57.3 and 14.4 g/g at 60% neutralization, respectively. As a crosslinking agent content increased, AUL increased but CRC significantly decreased. Additionally, soil pH evaluation confirms that SAP do not cause soil acidification.