Residual Lignin in Alkaline Pulps

Abstract

The final delignification stage starting at the point of 92–94% delignification proceeds slowly and usually accompanies the degradation and dissolution of polysaccharides. Therefore, the cook has to be interrupted in order to maintain a high pulp quality and yield, and further delignification is carried out by bleaching, generally under oxidative conditions using various bleaching agents. The lignin remaining in the pulp fibers at this stage is called residual lignin. The quantity and properties of this lignin determine pulp brightness and strength as well as the consumption of bleaching agents. The chemical and physical characteristics of residual lignin are therefore extremely important to an understanding of the fundamental parameters affecting pulping and bleaching.