What is Lignin?

Lignin is a complex, high molecular weight polymer that is critical in helping trees grow tall. It literally is the "glue" that holds everything together.

From Wikipedia:

Lignin is a chemical compound that is an integral part of the cell walls of some cells, e.g., tracheids, xylary fibres and sclereids of plants.

Lignin polymers are mostly made of phenylpropanoid units linked to each other through different kinds of bonds. Lignin polymers are probably network structures with a molecular weights on the order of 10,000 amu.

Lignin is the most abundant organic material on earth after cellulose. It is believed that lignin gives wood its stiffness and improves water transport. Lignin is thought to act as a kind of glue in the plant cell walls and give plants very effective protection against parasite attack. Lignin makes up about one-quarter to one-third of the mass of dry wood. In the chemical pulping process, lignin is removed from wood pulp before it is turned into paper, and the extracted lignin is used as a binder in particleboard, adhesive for linoleum, and raw material for processing into chemicals (such as DMSO and vanillin). The type of lignin (such as lignosulfonates and kraft lignins) used in industry depends upon the method that was used to extract it.