Synthesis and swelling property of superabsorbent starch grafted with acrylic acid/2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid

In order to develop starch-based superabsorbent polymers (SAPs) with high water absorbency, both acrylic acid (AA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) were graft copolymerized onto cassava starch, and St-g-AA-AMPS SAP was successfully synthesized. The effect of AA/AMPS molar ratio on the structure and swelling property of SAP was investigated.Introduction of AMPS units improved the storage modulus and crosslinking density of St-g-AA-AMPS SAP, and was beneficial in forming a perfect network structure. With increasing AMPS content, the equilibrium swelling ratio and swelling rate constant (k) of the SAP first increased and then decreased, and the maximum swelling ratio reached 1200.0 and 90.0 g/g in distilled water and brine respectively, resulting from the high ionization constant and hydrophilic ability of AMPS, and improved tolerance to brine. By introducing AMPS units, the re-swelling capability of SAP was improved, and more hydrogen bonds could form between molecules of water and SAP, leading to an increase in non-freezing bound water and freezing bound water, and the water retention of SAP was enhanced.Introduction of AMPS units improved the water absorption capacity, swelling rate, and water retention ability of St-g-AA-AMPS SAP, presenting wide application potential in agriculture and horticulture of desert regions. © 2017 Society of Chemical Industry.