Synthesis and performance of CMC/PAM-based interpenetrating network hydrogels for targeted urea delivery

This study reports the synthesis and comprehensive characterization of carboxymethyl cellulose (CMC) and CMC/polyacrylamide (CMC/PAM) interpenetrating polymer network (IPN) hydrogels for enhanced water retention and slow nutrient release. The CMC/PAM hydrogel was fabricated via free-radical polymerization and systematically benchmarked against a chemically crosslinked CMC hydrogel to elucidate structure-property-release relationships. FTIR, XRD, TGA, and SEM analyses confirmed successful IPN formation, enhanced structural stability, and a more interconnected porous architecture. Compressive testing revealed significant mechanical reinforcement, with the modulus increasing from 0.10 MPa (CMC) to 0.40 MPa (CMC/PAM). Swelling studies showed that the CMC/PAM hydrogel exhibited higher water absorption capacity (46 g g^-1) than CMC (32 g g^-1), following Fickian diffusion behavior during the initial stage. Urea release profiles displayed biphasic behavior for both systems; however, kinetic modeling using the Higuchi, first-order, and Korsmeyer-Peppas models demonstrated a markedly reduced diffusion constant in the CMC/PAM hydrogel, confirming improved release control due to increased network density and hydrogen bonding interactions. These results demonstrate that IPN formation effectively modulates nutrient transport, supporting the classification of the developed system as a slow-release fertilizer matrix for sustainable agricultural applications.