Deep eutectic solvent assisted ball milling pretreatment restructures spent mushroom substrate polysaccharides for enhanced biodegradable superabsorbent hydrogel swelling

A porous, high-strength PAA-g-DSMS hydrogel mulch was engineered from spent mushroom substrate via DES-ball milling and microwave grafting. • The hydrogel demonstrated high water absorption, strong water retention, and excellent film-forming performance. • As liquid mulch, it achieved 92.0% Chinese cabbage seed germination and superior soil moisture–temperature regulation over commercial products.. • Soil burial and composting confirmed biodegradability, low ecotoxicity, and increased abundance of beneficial soil fungi. Renewable polysaccharides from agricultural residues represent attractive alternatives for functional materials that address drought stress and plastic mulch pollution. In this study, the cellulose and hemicellulose polysaccharides present in spent mushroom substrate (SMS) were enriched with choline chloride/lactic acid deep eutectic solvents (DES) combined with ball milling. This synergistic pretreatment effectively increases the relative contents of cellulose and hemicellulose by promoting lignin depolymerization via acid catalysis and disrupting the lignin-carbohydrate complex structure, thereby improving the accessibility of reactive hydroxyl groups on polysaccharides. The resulting lignocellulosic material (DSMS) was grafted and copolymerised with acrylic acid under microwave irradiation to form a porous and high mechanical strength hydrogel (PAA-g-DSMS). PAA-g-DSMS exhibited high water absorption capacity, strong water retention and good film-forming performance. When used as liquid mulch, PAA-g-DSMS significantly improved soil moisture retention and temperature buffering capacity and made the seed germination rate of Chinese cabbage reach 92.0%, which was superior to commercial superabsorbent polymers and commercial liquid film. Soil burial and composting experiments further prove that it has biodegradability and low ecological toxicity and can also increase the abundance of beneficial soil fungi. This study highlights the critical role of renewable polysaccharides from agricultural waste in biodegradable mulching film, offering a sustainable solution for water saving agriculture and soil health management. Through DES-assisted ball milling and subsequent microwave-assisted graft copolymerization with acrylic acid, cellulose/hemicellulose (polysaccharides) extracted from mushroom residue is converted into a hydrogel that enhances soil moisture and temperature retention for improved crop growth. Download: Download high-res image (105KB) Download: Download full-size image