Biopolymer-based hydrogel formulations for improved 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 like starch (St) and carboxymethyl cellulose (CMC) by using glutaraldehyde (GA) as a crosslinking agent. There are numerous studies on starch (St) and CMC-based films produced by extrusion, as well as on starch-based hydrogels modified with synthetic polymers; however, only a few studies focus on hydrogels derived from natural polymers such as starch and CMC. 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. Swelling studies indicated that hydrogels with higher starch content achieved greater water uptake. The biodegradability study showed 67% degradation in soil after 45 days, which is remarkable. Sugar beet seeds germinated and grew well in the soil, reaching the highest seedling length of 6 ± 0.8 cm. The seedling growth of coated and uncoated seeds was assessed, and the coated seeds showed a significantly higher emergence length (6 cm ± 0.3 cm) compared to the uncoated seeds (3 cm ± 0.3). 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.