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The effect of black liquor exchange in the kraft cook on the tensile properties of Eucalyptus urograndis kraft pulp
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
2009 (English)In: O Papel cellulose, papel, impressão, ISSN 0031-1057, Vol. 70, no 4, 35-50 p.Article in journal (Refereed) Published
Abstract [en]

Xylan addition to kraft cooking has been shown to increase the tensile strength of the pulp but may also lead to a densification of the sheet. The main objective of this study was to correlate the molecular properties of black liquor xylan with its ability to increase tensile strength at a given sheet density. Black liquors were obtained from kraft cooks performed at different cooking temperatures and cooking times, which resulted in dissolved xylan with different degrees of substitution of uronic acids, different molecular weights, and connected to different amounts of lignin. These black liquors were added to the later part of subsequent kraft cooks. The results show that the degree of substitution of the black liquor xylan is of great importance when using it as an additive to the kraft cook in order to enhance pulp strength. Both, improved and deteriorated tensile strengths at given sheet densities were seen as a result of the black liquor exchange, depending on the charge of the added xylan. This illustrates that exchanging black liquor is an attractive tool in order to improve the physical properties of the produced paper if it is done wisely, but may cause impairments if the exchange is conducted in an incorrect manner. Furthermore, novel analytical tools made it possible to detect much higher uronic acid contents in xylan than previously reported.

Place, publisher, year, edition, pages
2009. Vol. 70, no 4, 35-50 p.
Keyword [en]
4-O-methyl-D-glucuronic Acid, Eucalyptus urograndis xylan, Hexenuronic acid, sheet density, Tensile strength
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-7715Scopus ID: 2-s2.0-67649977326OAI: oai:DiVA.org:kth-7715DiVA: diva2:12821
Note

QC 20100702

[O efeito da troca de licor negro em cozimento kraft nas propriedades de tração de polpa kraft de eucalyptus urograndis]

Available from: 2007-11-23 Created: 2007-11-23 Last updated: 2014-10-06Bibliographically 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

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Lindström, Mikael

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