Low‐Molecular‐Weight Lignin Derived from Cotton Stalks via γ‐Valerolactone Pretreatment for High‐Performance Hydrogel Fabrication

Lignin, an underutilized aromatic biopolymer from agricultural waste, is promising for functional hydrogels. However, the complex composition, molecular heterogeneity, and low active site accessibility of lignin severely restrict its practical applications. Traditional lignin extraction methods result in over 80% cleavage of β‐O‐4 bonds and a significant loss of phenolic hydroxyl groups. In this study, four different molecular weight lignins (F1‐F4) were obtained from cotton stalks via γ‐valerolactone pretreatment. The molecular weights of F1‐F4 were 5203, 2926, 1956, and 938g/mol, with total phenolic hydroxyl contents of 0.03, 0.09, 0.27, and 0.54 mmol/g, respectively. Compared with hydrogels of the high‐molecular‐weight lignin (F1), the low‐molecular‐weight lignin‐based hydrogel (F4) exhibited 3.32‐fold enhanced elasticity, 4.23‐fold improved conductivity, and 1.52‐fold higher antibacterial activity. Notably, the γ‐valerolactone pretreatment preserved β‐O‐4 bonds more effectively, while increasing the pore size by 1.57‐fold. These results indicated that the low‐molecular‐weight lignin with high phenolic hydroxyl content conferred the hydrogel with significantly enhanced elasticity, conductivity, and antibacterial activity, making it highly promising for applications in drug delivery, wound healing, and wearable biosensors. This work demonstrates a green route to valorize agricultural lignin into high‐performance hydrogel materials.