Lignin

From DictionGloss

Lignin is a substance related to cellulose that provides rigidity and together with cellulose forms the woody cell walls of plants and the cementing material between them.

Lignin is the major noncarbohydrate, polypenolic structural constituent of wood and other native plant material that encrusts the cell walls and cements the cells together. It is a highly polymeric substance, with a complex, cross-linked, highly aromatic structure of molecular weight about 10,000 derived principally from coniferyl alcohol (C₁₀H₁₂O₃) by extensive condensation polymerization. Higher heating value (oven dry basis): HHV=9111 BTU/LB (5062 CAL/G, 21178 J/G).

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In conservation, lignin refers to unpurified wood pulp commonly found in modern newsprint and other poor quality papers. It usually turns yellow over time and especially with exposure to sun light.