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  • 1.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Jansson, Zheng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Characterisation of dissolved spruce xylan in kraft cooking2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 4, p. 380-385Article in journal (Refereed)
    Abstract [en]

    Xylan dissolved during kraft cooking and later redeposited on fibre surfaces has been demonstrated to affect paper strength properties. Earlier studies have demonstrated that it is the xylan characteristics, rather than simply the amount of xylan, that influence the strength-enhancing effect of xylan. To use xylan optimally, it is useful to understand xylan’s beneficial characteristics and how cooking conditions affect them.

    In this study, spruce chips were kraft cooked under various cooking conditions and the xylan in the black liquor was characterized. We found that dissolved spruce xylan had a much higher amount of bound lignin than found in previous studies of xylan dissolved from hardwoods. The ionic strength of the cooking liquor affected the amount of dissolved xylan as well as the uronic acid content of the xylan.

  • 2.
    Jansson, Zheng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Characterization of Spruce Xylan and Its Potential for Strength Improvement2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Xylan dissolved during kraft cooking and later redeposited on fibre surfaces has been shown to give higher pulp yield and better strength properties. This is economically interesting from an industrial point of view. Many studies have been done to investigate xylan behaviour during kraft cooking, to discover the xylan-cellulose attachment mechanism, to find the optimal xylan retention or adsorption process, and to discover relations between xylan structure and strength enhancement. Most of them have concentrated on hardwood xylan. However, softwoods are the major raw materials for the pulp industries in the northern hemisphere. Earlier studies have shown that the xylan characteristics, rather than simply the amount of xylan, influence the strength-enhancing effect of xylan. To obtain optimal utilization of spruce xylan as a strength enhancer, it is essential to know what the beneficial xylan characteristics are and how cooking conditions affect the characteristics.

    In this study, kraft cooking of spruce chips was performed under varied cooking conditions and the xylan in the black liquor was precipitated and characterized. It was found that dissolved spruce xylan had a much higher amount of bound lignin compared to previous studies on xylan dissolved from hardwoods. Increased cooking temperature increased the dissolution rate of xylan. The lower alkali charge and higher ionic strength of the cooking liquor resulted in a lower amount of dissolved xylan. Apart from the effect of the amount, cooking conditions also affected substitution of dissolved xylan. Higher temperature and higher ionic strength led to a lower amount of MeGlcA, while the MeGlcA amount of dissolved xylan was preserved during lower alkali cooking.

    By distinguishing how different cooking conditions affect the characteristics of the xylan dissolved in the black liquor, xylans with different structures were designed to study their effects on pulp strength, that is, the addition of black liquors with certain known xylan characteristics in the kraft cooking process. It was found that the best effect of xylan on tensile strength occurred when the xylan penetrated some distance into the subsurface of the fibre wall. Both low molecular weight and high degree of substitution lowered the tendency of xylan to aggregate, which enabled the dissolved xylan to penetrate some distance into the exposed fibre surface. Upon beating, this xylan was exposed, thus facilitating improvement of fibre-fibre joint formation, which led to increased tensile strength.

  • 3.
    Li Jansson, Zheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Effect of Kraft Cooking Conditions on the Chemical Composition of the Surface and Bulk of Spruce Fibers2014In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 34, no 4, p. 291-300Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Li Jansson, Zheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Effect of kraft cooking conditions on the chemical composition ofthe surface and bulk of spruce fibers2011Manuscript (preprint) (Other academic)
  • 5.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Li Jansson, Zheng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Designing spruce xylan for higher tensile strength2011Manuscript (preprint) (Other academic)
  • 6.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Li Jansson, Zheng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Influence of spruce xylan characteristics on tensile strength of spruce kraft pulp2015In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 69, no 1, p. 1-7Article in journal (Refereed)
    Abstract [en]

    The aim of the study was to investigate the possibility to use spruce xylan more efficiently by possible relocation of dissolved xylan with certain characteristics from the first part of the kraft cooking to the later part, when precipitation occur. The characteristics of re-located xylan was controlled by replacing half the black liquor (BL) at a late stage of a kraft cook, with the same amount of black liquor containing spruce xylan with known molecular weight and content of uronic acid (UA). Pulp with addition of xylan with high amount of UA groups responded strongly on beating, resulting in improved tensile strength. It is proposed that the best effect of xylan on tensile strength occurs when the xylan penetrates some distance into the subsurface of the fiber wall. Both low molecular weight (M-w) and a high degree of substitution decreases the tendency of xylan to aggregate, which enables the dissolved xylan to penetrate some distance into the exposed fiber surface. Upon beating, this xylan will be exposed thus facilitating improved fiber-fiber joint formation, which leads to increased tensile strength.

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