Journal
JOURNAL OF WOOD CHEMISTRY AND TECHNOLOGY
Volume 34, Issue 4, Pages 291-300Publisher
TAYLOR & FRANCIS INC
DOI: 10.1080/02773813.2013.872661
Keywords
Kraft cooking; spruce; carbohydrate composition; fiber surface; lignin content
Categories
Funding
- VINNOVA's Branch Research Program
- Eka Chemicals
- Holmen
- SCA
- SmurfitKappa
- Stora Enso
- Sodra Cell
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By varying cooking temperature, alkali charge, ionic strength, and cooking time in Kraft pulping of spruce chips, pulps ranging between kappa numbers 20-80 were obtained. The unbleached Kraft pulp fibers were subjected to mechanical peeling in order to separate the surface material from the bulk of the fibers and the carbohydrate composition and lignin content of the two fractions were analyzed. As expected, the lignin and xylan contents were higher on the fiber surface than in the fiber wall. The percentage of xylan on the fiber surface was fairly constant, independent of different pulping conditions or degree of delignification. The lignin proportion on the fiber surface gradually decreased with decreasing kappa number. At a given kappa number, pulping at a higher temperature resulted in less lignin on the fiber surface, probably because of the higher solubility of lignin at higher temperature. Cooking at lower alkali charge also resulted in lower lignin content on the fiber surface at a given kappa number. In this case, there was more time available for degradation of the surface lignin since the lower alkali charge resulted in longer cooking time needed to reach a certain kappa number.
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