Transforming lignin into renewable fuels, chemicals, and materials: A review

Lignin, Lignin is a valuable carbon-rich feedstock and a by-product of the lignocellulosic biorefinery and paper industry. Despite being widely available, it is an under-utilized material. Lignin is the second most prevalent biopolymer with a polyaromatic structure present in the cell wall of vascular plants. However, its complex molecular structure and selective solubility in some solvents make its commercial feasibility largely unexplored. In recent decades, lignin has gained attention as a renewable raw biomaterial for synthesizing industrially important value-added materials such as adhesives, resins, foams, lubricants, composites, and high-value chemicals. Despite this, a significant portion of lignin produced in the pulp and paper mill ends up as boiler fuel for power and heat production. The production of lignin from different methods and sources is often compared and questioned due to handling and environmental issues resulting from excessive production. This review paper discusses the structure of lignin, its types, extraction methods, modification via thermal and chemical approaches, applications, prospects, and challenges.