Chemical structure of lignin polymer

Lignin is the second most abundant natural polymer in the world after cellulose, which is known as a cheap, non-toxic and biodegradable material, a suitable alternative to oil-based polymers. Researchers have made great efforts to identify the chemical structure of lignin. However, there are still many problems in replacing monomers obtained from crude oil used in the manufacture and synthesis of polymeric materials, such as polyurethanes, with lignin. One of the major problems in identifying this natural polymer is the lack of specific and standard protocols.