General term for a collection of polysaccharides found in wood, having a chemical structure similar to that of cellulose (hence the name "'hemi cellulose"). In papermaking, the only necessary ingredient from the wood or plant source is cellulose, and hemicelluloses and lignin—a material that binds the cellulose fibers together—are contaminants and reduce paper quality and permanence, and must be removed from paper pulp before papermaking begins. (See Pulping.)
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