Review of lignin extraction and isolation processes: from lignocellulosic biomass to added-value materials

Lignin is one of the three major components of the cell wall of lignocellulosic biomaterials. It is the second-most abundant polymer in nature. It is a complex and heterogeneous polymer found in the cell walls of lignocellulosic biomass. Lignin’s predominant composition, rich in carbon and aromatic structures, enhances its value by enabling the development of high-value chemicals and bio-based materials. As one of the most affluent natural renewable sources of aromatic structures and the world’s second-largest renewable source of carbon, lignin possesses a thermal value comparable to that of carbon. Its aromatic constituents exhibit unique chemical properties and significant bioactive effects, making lignin a crucial material in various advanced applications. Different chemical fractionation methods have been designed to overcome the lignocellulosic biomass’ obstacle to extracting lignin biopolymer. Lignin fractionation is a process that involves separating lignin from other components of biomass feedstocks, such as cellulose and hemicellulose. This process is commonly used in the paper and pulp industry to obtain valuable lignin derivatives that can be used in various applications, including, among others, biofuels, chemicals, and biomaterials. In this review, we provide a comprehensive chemical overview of current processes for extracting technical lignins from wood and lignocellulosic biomass, critically evaluating the advantages and limitations of each method.