Recent advances in lignin from forest residue for hydrogel application

Forest waste is a crucial by-product of industries such as sawmills and timber processing facilities. Lignin is extracted from these residues; due to its high abundance, sustainability, inexpensiveness, and good functionality, it is a low-cost, eco-friendly, green, readily available biomass material for hydrogel synthesis. Various techniques, including chemical pulping (alkaline pulping, kraft pulping, soda pulping), acidic pulping (acid sulfite pulping, acidic hydrolysis), organosolv fractionation including microwave-assisted extraction, ionic liquid dissolution, physical processes (steam explosion, homogenization, ultrasonication) and biochemical reactions (enzymatic hydrolysis), are all used to extract lignin from forest residues. The extracted lignin is then processed into a hydrogel through physical and chemical interactions. This review highlights some essential lignin extraction processes, lignin-based hydrogel production techniques, advanced technologies that can be used for hydrogel synthesis (freeze-thawing, stereo complex formation, microwave-assisted synthesis, one-pot synthesis, heat-induced synthesis), and its potential significance of lignin-based hydrogel in different fields such as biomedical and pharmaceutical sectors.