2. Sources of Lignin

Lignin is a complex aromatic polymer that serves a crucial structural function in plant cell walls, imparting stiffness and durability to diverse biomass forms. Lignin, the second most prevalent biopolymer, has attracted considerable attention owing to its sustainability and prospective applications. This chapter examines several lignin sources, such as the pulp and paper industry, sugarcane bagasse, and agricultural residue. The composition and structure of lignin differ based on the plant source, leading to unique varieties (hydroxyphenyl, guaiacyl, and syringyl) derived from certain monolignols. The pulp and paper industry is the greatest lignin producer, creating around 50–70 million tons yearly as a by-product of the pulping process. The standard techniques for lignin extraction predominantly encompass kraft, sulfite, soda, and organosolv procedures. Each of these methods utilizes distinct chemical treatments to isolate lignin from lignocellulosic biomass, and they are extensively employed in industrial applications. Lignin possesses significant potential in several applications, including composite materials, coatings, adhesives, biofuels, and biochemicals.