Structural changes in residual kraft pulp lignins. Effects of kappa number and degree of oxygen delignification
2003 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 18, no 4, 395-399 p.Article in journal (Refereed) Published
Softwood kraft pulps in the kappa number range of approximately 10-50 were prepared in the laboratory. On subsequent oxygen delignification using single or double oxygen stages, the conditions were chosen such that all pulps reached a similar kappa number. As a consequence, different brightness values were obtained after the oxygen stage. The darker pulps were found to require considerably more hydrogen peroxide to reach full brightness (89% ISO). On selected pulps, the content of phenolic hydroxyl groups and the general structural features of the residual lignin were determined by periodate oxidation and 2D NMR respectively. It was found that the number of phenolic groups increased as a function of cooking time and that oxygen delignification led to a decrease which was related to the severity of the oxygen stage. Furthermore, a continuous decrease in the number some of the major lignin inter-unit linkages was found to occur during the cooking stage. After the oxygen stage, however, an apparent increase in the number of these linkages was observed in some of the pulp lignins. These results are discussed with reference to the known features of residual lignins in kraft pulps and an attempt is made to rationalize the structural changes that occur during pulping and oxygen delignification.
Place, publisher, year, edition, pages
2003. Vol. 18, no 4, 395-399 p.
bleachability, kappa number, kraft pulping, lignin content, NMR analysis, oxygen delignification, phenols, TCF-bleaching, tcf-bleachability, cooking, degradation, brightness, kinetics
IdentifiersURN: urn:nbn:se:kth:diva-23158DOI: 10.1515/hf.2006.026ISI: 000188873000006OAI: oai:DiVA.org:kth-23158DiVA: diva2:341856
QC 201005252010-08-102010-08-10Bibliographically approved