Isolation of Lignin from Pulp

Isolation of residual lignin from a chemical pulp, especially from a bleachable grade, has been a difficult task since the residual lignin content in pulp is relatively low and is probably linked chemically to the carbohydrates. A method for the quantitative isolation of residual lignin in chemical pulp for subsequent structural studies was developed in the early 1980s (Yamasaki et al. 1981a,b). The procedure is based on selective hydrolysis and dissolution of the carbohydrates in pulp by commercially available cellulolytic enzymes leaving lignin as an insoluble residue. The method was adapted from the enzymatic method first reported by Pew 1957, Pew and Weyna (1962) and later adapted by Chang et al. (1975) for the isolation of lignin from wood. The main difference between the two procedures is that chemical pulp, unlike wood, is digestible by cellulolytic enzymes without ball-milling. Consequently, this method provides an ideal method for the isolation of the residual lignin in chemical pulps without structural modification.