On the Mechanism of Pulp Bleaching. V. Further Investigations on the Residual Lignosulfonic Acid in Unbleached Sulfite Pulp

Abstract

Abstract 1) By beating unbleached sulfite pulp step by step and changing the beating water, four fractions of residual lignosulfonic acids were obtained. Analytically not very distinct differences were observed between these fractions. 2) The residual lignosulfonic acids isolated by beating and by dimethyl sulfoxide were oxidized with nitrobenzene, and the yields of vanillin obtained from these lignin preparations were comparad with that from ordinary lignosulfonic acid separated from waste liquor. Almost no difference was observed. 3) The amounts of residual lignosulfonic acid dissolved by beating and by dimethyl sulfoxide extraction were in good agreement with those calculated from the amount of the residual lignosulfonic acid remaining in the pulp, thus proving the accuracy of the estimation. Approximately 40 and 20% of the total lignin in unbleached sulfite pulp were dissolved by beating and by dimethyl sulfoxide extraction respectively.