Upcycling cornstalk waste into bio-superabsorbent polymers via graft polymerization of ultrasonically fractionated crude cellulose for agricultural applications

A cornstalk–derived superabsorbent polymer was prepared by grafting acrylic acid and bio-based itaconic acid, with the synthesis conditions systematically optimized using response surface methodology. Response surface analysis revealed significant linear and quadratic effects of the formulation variables, with a significant interaction between crosslinker concentration and itaconic acid content. Moderate formulation levels provided a favourable balance between network formation and swelling performance, whereas excessive crosslinking and high itaconic acid content decreased water uptake. The cellulose-based superabsorbent polymer exhibited a maximum absorption capacity of 520 g/g in deionized water and a reduced uptake in saline media, reflecting the effect of ionic strength on swelling. Swelling progressively decreased over successive wet–dry cycles, while the material retained substantial swelling capacity after four cycles. Complementary SEM, TGA, solid-state NMR, and XRD analyses were performed to establish structure–property relationships and confirm material integrity.