Studies on the Oxidative Degradation of Lignin (VIII)

Abstract

For better understanding on the physical properties of lignosulfonate and its peracetic acid-degradation product as a dispersing agent, the dispersing effect of both lignin preparations to ZnO was investigated. The water-soluble part of dioxane lignin degraded with peracetic acid was also used as a lignin dispersant.These three lignin preparations were fractionated to the smaller fractions, respectively, which ware different in the molecular weight and the content of the dissociating groups, such as sulfonyl and carboxyl groups. The dispersing effect of the fractions thus obtained was compared by measuring the sedimentation volume and the viscosity of a ZnO slurry. The adsorption amount of each fraction on a ZnO particle was also determined.From the results, it was indicated that the molecular weight of some fractions of each lignin preparation which have a best dispersing effect for ZnO slurry, is in the range from 8×103 to 2×104. But, the higher or lower polymer diminished the effect. The amount of lignin absorped on ZnO particle increased with increasing the molecular weight. It was also found that the main fraction of lignosulfonate has better dispersing effect for ZnO than it of the other two lignin preparations.Although a dissociating group, such as sulfonyl or carboxyl group is necessary for making a lignin dispersant, the dispersing ability of a lignin preparation did not correlate so much with the content. So this relationship seems to be a secondary effect for dispersing ZnO.