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Characterization of Spruce Xylan and Its Potential for Strength Improvement
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. (CRUW)
2013 (English)Licentiate 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , v, 34 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:10
Keyword [en]
xylan, paper strength
National Category
Chemical Process Engineering
Identifiers
URN: urn:nbn:se:kth:diva-119920ISBN: 978-91-7501-667-2 (print)OAI: oai:DiVA.org:kth-119920DiVA: diva2:612807
Presentation
2013-04-08, Rånbyrummet, Teknikringen 56, plan 2, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130326

Available from: 2013-03-26 Created: 2013-03-25 Last updated: 2013-03-27Bibliographically approved
List of papers
1. Characterisation of dissolved spruce xylan in kraft cooking
Open this publication in new window or tab >>Characterisation of dissolved spruce xylan in kraft cooking
2011 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 4, 380-385 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Stockholm: , 2011
Keyword
Kraft cooking, spruce, dissolved xylan, molecular weight, uronic acid content
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-73364 (URN)000298868000003 ()2-s2.0-84855548125 (Scopus ID)
Note
QC 20120221Available from: 2012-02-02 Created: 2012-02-02 Last updated: 2017-12-08Bibliographically approved
2. Effect of kraft cooking conditions on the chemical composition ofthe surface and bulk of spruce fibers
Open this publication in new window or tab >>Effect of kraft cooking conditions on the chemical composition ofthe surface and bulk of spruce fibers
2011 (English)Manuscript (preprint) (Other academic)
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-120002 (URN)
Note

QS 2013

Available from: 2013-03-26 Created: 2013-03-26 Last updated: 2013-03-26Bibliographically approved
3. Designing spruce xylan for higher tensile strength
Open this publication in new window or tab >>Designing spruce xylan for higher tensile strength
2011 (English)Manuscript (preprint) (Other academic)
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-120003 (URN)
Note

QS 2013

Available from: 2013-03-26 Created: 2013-03-26 Last updated: 2013-03-26Bibliographically approved

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