Starch-Based Hydrogel Development and Its Impact on Seed Coating Performance

Bio-based superabsorbents have emerged as promising polymeric materials due to their excellent water retention capabilities and multifunctionality, particularly as active agent carriers and soil conditioners. However, the extensive use of conventional petroleum-derived superabsorbents poses significant environmental sustainability concerns. In this study, biodegradable superabsorbent hydrogels with a high bio-based content (90%) were synthesized from natural polymers—starch (St) and carboxymethyl cellulose (CMC)—using glutaraldehyde (GA) as a crosslinking agent. Hydrogels were prepared with varying St-to-CMC ratios and different GA concentrations to investigate their structural, swelling, and degradation behaviors. The resulting hydrogels demonstrated a remarkable water uptake ability of 17.5 g/g, attributed to their porous morphology, as revealed by scanning electron microscopy (SEM), and the presence of polar functional groups and crosslinked networks (acetal and hemiacetal linkages), as confirmed by Fourier transform infrared (FTIR) spectroscopy. SEM analysis also showed that increasing the GA concentration led to denser, more compact structures with smaller pore sizes. Swelling studies indicated that hydrogels with higher starch content achieved greater water uptake. Biodegradability assessments demonstrated the environmental friendliness of the materials, with mass loss reaching up to 90% in soil burial experiments. These findings suggest that St-CMC hydrogels crosslinked with GA have strong potential for agricultural applications as water-retaining soil conditioners or controlled-release platforms.