Abstract
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.