Structural Changes in Lignin During Kraft Cooking Part 3. On the Structure of Dissolved Lignins

Abstract

Abstract Two series of pine kraft lignins were prepared by a) normal kraft cooks to different pulp yield levels and precipitation of the lignins from the black liquors by acidification and b) by successive acidification of the black liquor obtained from a flow-through cook. All the lignins were extensively purified, subjected to elemental and methoxyl analysis and subsequently acetylated. Quantitative 13C-NMR analysis was carried out on acetylated samples and the results were combined with the results of phenolic group determination by means of aminolysis and with elemental analysis data. The various acetylated lignins were also subjected to analysis by size exclusion chromatography. All results are discussed with reference to known features of kraft cooking and of kraft lignins.