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Influence of birch xylan adsorption during kraft cooking on softwood pulp strength
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-2900-4713
2005 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 20, no 4, 436-441 p.Article in journal (Refereed) Published
Abstract [en]

The dissolution, degradation and redeposition of xylan in the kraft cooking of birch pulp were investigated. The molecular weight of the dissolved xylan was determined through gel permeation chromatography, and the loss in molecular weight could be correlated with the amount of degraded xylan in the initial stages of the kraft cook. This indicates that peeling is the only significant xylan degradation reaction taking place early in the cook. Two different birch black liquors containing xylan with molecular weights of 12.20 g/mol and 5.95 g/mol, respectively, were added to softwood kraft cooks in order to determine the effect of birch xylan on pulp strength properties. The results show an increase in both tensile strength and tensile stiffness. The magnitude of the strength increase was greatly affected by the molecular weight of the xylan added. Adding high-molecular-weight xylan increased the tensile strength by more than 10%, as measured at a beating degree of 1000 PFI revolutions. Tensile stiffness was also increased by xylan addition, though more so when the xylan was of high rather than low molecular weight.

Place, publisher, year, edition, pages
2005. Vol. 20, no 4, 436-441 p.
Keyword [en]
kraft pulping; hydroxyl ion concentration; xylan; hemicellulose; dissolution; degradation; precipitation; molecular weight; surface properties; paper strength; adsorption
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-7712DOI: 10.3183/NPPRJ-2005-20-04-p436-441ISI: 000235258200010Scopus ID: 2-s2.0-30344439844OAI: oai:DiVA.org:kth-7712DiVA: diva2:12818
Note
QC 20100702Available from: 2007-11-23 Created: 2007-11-23 Last updated: 2010-07-02Bibliographically approved
In thesis
1. Xylan Reactions in Kraft Cooking: Process and Product Considerations
Open this publication in new window or tab >>Xylan Reactions in Kraft Cooking: Process and Product Considerations
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Xylan is the main hemicellulose in birch, eucalyptus, and most other hardwood species. During kraft pulping a series of chemical reactions and physical processes involving xylan takes place. The processes studied here are the following: dissolution, degradation, redeposition onto the fibres, side-group conversion, and cleavage of side groups off the xylan backbone. The side group in native xylan consists of methylglucuronic acid, which is partly converted into hexenuronic acid during kraft cooking. Hexenuronic acid affects the pulp in terms of increased brightness reversion and reduced bleachability. The kinetics of the side-group cleavage and conversion reactions were studied using various analytical tools. The study revealed that the most common methods for methylglucuronic acid quantifcation can be signifcantly improved in terms of accuracy. A modifcation and combination of two of the methods was suggested and evaluated.

In order to minimise the hexenuronic acid content, a common suggestion involves the use of a high cooking temperature. The kinetic study found that the degree of substitution of pulp xylan is only slightly affected by temperature, and that the observed effects are likely to be more associated with the xylan content of the pulp than with the hexenuronic acid content of the xylan. For the dissolved xylan, however, the degree of substitution indicated a high temperature dependency for birch kraft cooking.

By collecting black liquors at different stages in the cook, different molecular properties of the dissolved xylan was obtained. The liquors were charged at later parts of the cook, making the dissolved xylan to reattach to the fibres. Depending on the molecular properties of the added xylan, the tensile strength properties of the produced paper were improved. These improvements in paper properties were correlated to the molecular behaviour of the added xylan in solution.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. [11], 73 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:78
Keyword
Xylan, Kraft cooking, Paper strength, Sheet density, Methylglucuronic acid, Hexenuronic acid
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-4551 (URN)978-91-7178-819-1 (ISBN)
Public defence
2007-12-14, F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100702Available from: 2007-11-23 Created: 2007-11-23 Last updated: 2010-07-02Bibliographically approved
2. Xylan reactions in kraft cooking and their influence on paper sheet properties
Open this publication in new window or tab >>Xylan reactions in kraft cooking and their influence on paper sheet properties
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Xylan is the main hemicellulose in birch, eucalyptus, and most other hardwood species. During kraft pulping a series of chemical reactions and physical processes involving xylan take place. The processes studied in this thesis are the following: dissolution, degradation, redeposition onto the fibres, side group conversion, and cleavage of side groups off the xylan back bone. The side group in native xylan consists of methylglucuronic acid, which is mainly converted into hexenuronic acid during kraft cooking. Hexenuronic acid affect the pulp in terms of increased brightness reversion and deteriorated bleachability. The kinetics of the side group cleavage and conversion reactions were analysed using various analytical tools. The study revealed that the most commonly used methods for methylglucuronic acid measurements are not as accurate as has been claimed in the literature. A modification of two of the methods was suggested and evaluated.

A common practice used to minimise the hexenuronic acid content involves use of a high cooking temperature. The kinetic study showed that the degree of substitution of pulp xylan is only slightly affected by temperature, and that the observed effects are likely to be more associated with the xylan content of the pulp than with the hexenuronic acid content of the xylan. For the dissolved xylan, however, the degree of substitution showed a high temperature dependency and moreover it was always higher than in the pulp.

Xylan itself is known to have the capacity to increase the strength of the manufactured pulp. This knowledge was applied by exchanging cooking liquors between birch kraft cooks, in which a high amount of xylan is dissolved, and spruce cooks, which contain very small amounts of native xylan. This seems like an attractive alternative for softwood kraft cooking, since both the tensile strength and stiffness increased significantly. The magnitude of the strength increase was correlated with the molecular weight of the added xylan and with the increased surface charge of the fibres.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 53 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:01
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-3850 (URN)
Presentation
2006-02-17, STFI-salen, STFI, Drottning Kristinas väg 53, 100 44 Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101111Available from: 2006-02-14 Created: 2006-02-14 Last updated: 2010-11-11Bibliographically approved

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