Extraction of Lignin and Modifications

Lignin is considered the second most abundant renewable material after cellulose. It is a natural amorphous macromolecule that confers rigidity, impermeability, and resistance to the structure of plants. Due to its efficiency as a biopolymer, lignin has received much attention over the years. In its structure, lignin can present several functional groups that make it a promising material in the use of synthesis to produce new compounds, such as the presence of aliphatic, phenolic, carboxylate, and sulfonate hydroxyl groups. Such complex and heterogeneous chemical composition poses a principal challenge for its utilization. In addition, the amount of lignin varies significantly with biomass origin, processing, and isolation method. Thus, the demand for new strategies is being developed to improve the conversion and availability of this lignin, as an option to use a low-cost material that has a high capacity to expand the recovery of renewable waste. This chapter aims to present different methods of lignin isolation, especially in agro-industrial residues, as the main chemical modifications for applications of new materials with high added value.