Selectivity Improvement During Oxygen Delignification by Adsorption of Polymeric Additives, 2002 International Pulp Bleaching Conference Proceedings

Steven Violette and Adriaan van Heiningen

Pulp-strength loss during oxygen delignification is caused by cellulose depolymerization resulting from attack by radicals generated during delignification reactions. The objective of the present research was to investigate the use of radical-scavenging polymeric additives that adsorb on the cellulose surfaces where protection from these radicals is needed. Among the polymers tested were starch, carboxymethylcellulose, galactomannan, xylan, and glucomannan. The highest increases in lignin-cellulose selectivity were observed for guar galactomannan as the adsorbed additive, with significant improvements at charges as low as 0.3% on pulp. At 2.0% guar on pulp, the selectivity improvement was about 30%. The change in cellulose degree of polymerization (DP) is expressed as the number of polymer chain scissions, and the kappa number and cellulose DP changes are corrected for alkali extraction in the absence of oxygen. This method of analysis provides a fundamental understanding of the mechanism of oxygen delignification. Polymer adsorption on pulp was measured by sugar analysis using high performance anionic exchange chromatography (HPAEC). Selectivity measurements were related to the adsorbed amount of polymer additive.