| The nature of the residual extractives in kraft pulps and their impact on oxygen dell unification was investigated with tab prepared kraft pulps followed by oxygen delignification with one softwood species, loblolly pine (Pinus taeda L.) and two hardwood species, trembling aspen (Poplus tremuloides M.) and white birch (Betula papyrifere M.).; The amounts of residual extractives in the kraft pulps and oxygen-delignified pulps and their impact on the usual methods of lignin determinations were investigated. The lignin analyses investigated were kappa number and Klason lignin in conjunction with acid-soluble lignin. In the hardwoods, significant amounts of extractives remained after kraft pulping and oxygen delignification. These residual extractives in the hardwood pulps had an impact on the lignin determination, more so on the acid lignin method than kappa number.; The degree of oxygen delignification of the hardwood kraft pulps was significantly lower than that of the pine pulp based as assessed through the kappa number. Much of the difference could be attributed to the variation of the residual extractives and hexeneuronic acid content in the unbleached and oxygen-delignified pulps, as they interfered with the conventional lignin determination methods. Thus, after a correction for the contributions from these non-lignin components to the lignin analyses, the hardwood kraft pulps displayed a response to oxygen delignification similar to the pine pulps.; Both the kraft pulping and the subsequent oxygen delignification significantly altered the composition of the residual extractives in pulps. Residual extractives in unbleached and oxygen-delignified kraft pulps were analyzed with GC and GC-MS. The main residual extractives were sterols, steryl esters, and fatty acids. Unsaturated fatty acids (mainly 9,12-octadecadienoic acid) were effectively removed during oxygen delignification. |
