1. n. 
The component of a tree that is extracted in the paper-manufacturing process and used as an additive in drilling fluids. Specifically, lignin is a highly polymerized, amorphous material that makes up the middle lamella of woody fibers and cements the fibers together. Methoxy groups are abundant on the lignin structure, giving lignin many reactive sites and promoting its water solubility. In paper manufacturing, lignin is dissolved from wood chips. In the sulfite paper process, the liquor byproduct contains wood sugars and lignosulfonate. The wood sugars are removed and the lignosulfonate is used as a clay deflocculant. In the kraft paper process, lignin is solubilized by caustic soda. Kraft lignin must be further reacted to make a functional drilling-fluid additive.