Transforming Wheat Straw into Superabsorbent Polymers for Sustainable Agricultural Management

The massive accumulation of agricultural waste, such as wheat straw, and its disposal by burning pose significant environmental challenges. This study explores a sustainable solution by converting wheat straw into composite superabsorbent polymers (SAPs)-superabsorbents contain both synthetic and biodegradable fragments-for improved agricultural water and nutrient management. Wheat straw (WS) was sequentially processed via acid and alkaline hydrolysis to yield fractions with different lignin contents, which were then carboxymethylated (CMWS-Ac and CMWS-Al) to enhance hydrophilicity. These derivatives were incorporated at 20 and 33 wt. %. into SAPs synthesized by copolymerization with acrylamide and acrylic acid. The CMWS-Al-based SAPs exhibited superior properties, including higher equilibrium swelling ratios (up to 566 g/g in water), excellent mechanical strength, and robust gel structure, as confirmed by rheological studies. Furthermore, SAPs demonstrated a significant capacity to retain urea in sand columns, with SAP-CMWS-Al-33 achieving 56% urea retention, highlighting their potential for mitigating fertilizer leaching. The results establish a correlation between the extent of straw processing, the physicochemical properties and lignin content of the derivatives, and the performance of the final SAPs. These wheat straw-based SAPs present a promising, sustainable technology for enhancing soil moisture retention, improving fertilizer use efficiency, and valorizing agricultural waste.