Structure and Properties of Lignin

Abstract

Lignin is a phenolic natural polymer, second only to cellulose. It can be extracted from lignocellulosic biomass through various chemical, physical, mechanical, and enzymatic treatments. The chemical structure and properties of the extracted lignin are mainly depended on the extraction method, vegetal species, location, season, etc. Based on the separation method, several types of lignin, also called technical lignin, could be obtained, including alkali lignin/kraft lignin, lignosulfonate, organosolv lignin, milled wood lignin (MWL), klason lignin, and hydrolytic lignin. The separation conditions can influence the cross-linked structure and molecular weight distributions of the technical lignin products. By far, lignin is mainly regarded waste or by-product streams from paper pulping mills and cellulosic ethanol plants with a limited application for heat and power generation. However, the abundant availability and unique structure of lignin make it a potential feedstock for the synthesis of biochemicals and biopolymers such as surfactants/dispersants, carbon fibers, phenolic resins, epoxy resins, and polyurethane resins, etc.