Hydrogel Based on Starch and Poly(Ethylene Terephthalate) Recycling Products for the Slow Release of Urea

ABSTRACT This study focused on developing a novel polymeric hydrogel for agricultural applications, addressing the challenges of nutrient retention and controlled release. The hydrogel was synthesized using starch as a matrix and incorporated dPET, a byproduct of polyethylene terephthalate depolymerization, as a hydrophobic modifier. Urea was included as fertilizer. The dPET, was synthesized via a sustainable microwave‐assisted method, was characterized to confirm its successful synthesis. Hydrogels were prepared with varying dPET content (0%, 20%, 50%, and 65%). The 65% dPET hydrogel exhibited significantly reduced water uptake (from 1061% to 226%) and improved brittleness compared with the control. Thermal analysis revealed a decrease in the stability, with the onset of degradation shifting from 330°C to 135°C. Subsequently, urea (5, 10, and 20 wt.%) was incorporated into the hydrogel formulations. Evaluation using corn and onion crops demonstrated that the hydrogel with 35% starch and 65% dPET achieved a 60% reduction in urea release compared to free urea, while maintaining a slow and controlled release profile. Importantly, none of the hydrogel formulations inhibited crop growth and development. These findings contribute significantly to the development of cost‐effective and eco‐friendly fertilizers for sustainable agriculture.