Humic acid-crosslinked sodium carboxymethyl cellulose/starch superabsorbent polymers: Swelling kinetics, cytotoxicity, and hygiene applications.

Superabsorbent hydrogels are inorganic or organic hydrophilic polymer networks that have the capacity to absorb and hold large amounts of water in 3D (three-dimensional) networks, up to 500-1500 g/g. Because of their high hydrophilicity, non-toxicity, biocompatibility, biodegradability, and natural origin, polysaccharides have attracted a lot of interest as the building blocks for the synthesis of superabsorbent polymers. These qualities make them viable candidates for a variety of uses. In this study, a novel, environmentally friendly semi-interpenetrating anionic hydrogel based on carboxymethyl cellulose (CMC), humic acid, and starch was developed as a superabsorbent polymer (SAP). The synthesis conditions were tuned to get the maximum swelling ratio of the SAP. SAP4 has an equilibrium water absorption capacity of 332.11 ± 1.79 g g-1 in distilled water, which is higher than that of other SAPs; in 0.9 wt% NaCl, the capacity is 55.44 ± 0.36 g g-1. A strong correlation was observed between the water absorption behavior and the swelling kinetics, which were well described by the Schott pseudo-second-order and Fickian diffusion models. SAP1, SAP3, and SAP4 showed Fickian diffusion in distilled water, while SAP2 exhibited slightly non-Fickian behavior. In 0.9 wt% NaCl solution, all SAPs followed Fickian diffusion. The close agreement between Q∞ and Qeq and high R2 values confirmed the reliability of Schott's model. After three swelling cycles, SAP2, SAP3, and SAP4 retained 90.28 ± 0.89%, 91.57 ± 1.54%, and 92.86 ± 0.79% of their initial water absorption capacities, respectively. Moreover, the cytotoxicity results indicated that the SAP hydrogel exhibited acceptable cell viability under the tested conditions. These findings suggest that the developed SAPs could serve as effective and sustainable materials for future hygiene applications.