Knoevenagel condensation for malonate-grafted dialdehyde cellulose: Tuning mechanical and swelling properties of poly(acrylic acid-co-itaconic acid) bio-SAPs.

The development of high-performance bio-based superabsorbent polymers (BioSAPs) remains a major challenge in the transition toward sustainable materials. In this study, dialdehyde cellulose (DAC), obtained by periodate oxidation of cellulose extracted from banana fiber residues, was functionalized through a β-alanine-catalyzed Knoevenagel condensation with diethyl malonate. Unlike conventional Schiff-base modifications, this approach generates stable carbon‑carbon linkages that are resistant to hydrolysis under typical swelling conditions. Functionalization was supported by FTIR, XRD, and conductometric titration, which showed an increase in carboxylate content from 1.29 ± 0.19 to 3.32 ± 0.21 mmol g-1 with increasing malonate content. The resulting DACMal derivatives were incorporated into poly (acrylic acid-co-itaconic acid) networks via free-radical polymerization. SEM revealed a highly porous interconnected structure, while rheological measurements showed enhanced storage modulus and mechanical stability with increasing DACMal functionalization. The BioSAPs exhibited an exceptional equilibrium swelling capacity of 1556 ± 58 g g-1 in distilled water and 124 ± 11 g g-1 in 0.9 wt% NaCl at an optimal DACMal0.25 eq loading of 5 wt%. In addition, the modified BioSAPs retained 89% of their initial absorption capacity after four swelling-drying cycles, compared with 67% for unmodified DAC-based systems. These results demonstrate the potential of Knoevenagel-modified cellulose for durable and high-performance BioSAPs.