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Changes in the lignincarbohydrate complex in softwood kraft pulp during kraft and oxygen delignification
KTH, Superseded Departments, Fibre and Polymer Technology.ORCID iD: 0000-0002-8614-6291
(inventia)
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KTH, Superseded Departments, Fibre and Polymer Technology.
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2004 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 58, no 6, 603-610 p.Article in journal (Refereed) Published
Abstract [en]

Three kraft pulps in the kappa number range between 50 and 20 and the same pulps oxygendelignified to similar lignin contents (kappa approximately 6) were analyzed for lignincarbohydrate complexes (LCC) by a method based on selective enzymatic hydrolysis of the cellulose, and quantitative fractionation of the LCC. Between 85 and 90% of residual lignin in the unbleached kraft pulp and all residual lignin in the oxygendelignified pulps were isolated as LCC. Three types of complexes were found; viz., xylanlignin, glucomannanligninxylan and glucanlignin complexes. After pulping to a high kappa number, most of the residual lignin was linked to xylan. Different delignification rates were observed so that most of the residual lignin was linked to glucomannan when the pulping was extended to a low kappa number. With increasing degree of oxygen delignification, a similar trend in the delignification rates of LCC was observed so that the residual lignin was increasingly linked to glucomannan. Complex LCC network structures seemed to be degraded into simpler structures during delignification. The differences in delignification rates are discussed with reference to the solubility properties and structural differences of LCC, and to morphological aspects of the pulp.

Place, publisher, year, edition, pages
2004. Vol. 58, no 6, 603-610 p.
Keyword [en]
bleachability, kappa number, kraft pulping, lignin-carbohydrate complex (LCC), oxygen delignification, residual lignin, specific absorptivity
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-7818DOI: 10.1515/HF.2004.114ISI: 000224277300005Scopus ID: 2-s2.0-8344282690OAI: oai:DiVA.org:kth-7818DiVA: diva2:12954
Note

QC 20150727

Available from: 2005-10-20 Created: 2005-10-20 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Lignin polysaccharide networks in softwood and chemical pulps: characterisation, structure and reactivity
Open this publication in new window or tab >>Lignin polysaccharide networks in softwood and chemical pulps: characterisation, structure and reactivity
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The chemical interactions between the main wood components i.e., cellulose, hemicelluloses and lignin are of fundamental importance for understanding the chemical aspects of wood formation and its reactivity during fibre processing e.g during chemical pulping of wood. Future progress in the development of new high value products from wood will greatly depend on a detailed knowledge of how the fibre elements interact with each other in the biological material. The existence of covalent bonds between lignin and carbohydrates (LCC) has been one of the most controversial issues in the field of wood chemistry. Only until recently, the existence of such bonds has in its entirety been shown by way of indirect analyses, normally suffering from low yields obtained at rather drastic conditions. Furthermore, previous studies on LCC have been targeted on studying the specific lignin carbohydrate linkage and less emphasis has been put on the whole LCC networks. Detailed structural studies of entire LCC are therefore of importance in understanding the chemistry involved in wood formation and wood reactivity.

The aim of this study was to isolate intact LCC from wood and corresponding chemical pulps made from it in quantitative yield and to clarify their detailed chemical structure. For the first time, a method for the quantitative analysis of lignin-carbohydrate complexes (LCCs) in softwood is presented and it could be concluded that no carbohydrate-free lignin was present in these wood fibres. From mildly ball-milled wood, all lignin was isolated as LCCs in a sequence involving a partial enzymatic hydrolysis of cellulose, subsequent swelling and quantitative dissolution, into 4 major fractions; a galactoglucomannan-lignin-pectin LCC (GalGlcMan-L-P) containing ~8% of the wood lignin, a glucane LCC (Glc-L) containing ~4% of the wood lignin, a xylan-lignin-glucomannan network LCC (Xyl-L-GlcMan) (with a predominance of xylan over glucomannan) containing ~40% of the wood and a glucomannan-lignin-xylan network LCC (GlcMan-L-Xyl) (with a predominance of glucomannan over xylan) containing ~48% of the wood lignin.

From unbleached kraft pulps, 85 - 90% of residual lignin was found to be chemically bonded to carbohydrates. The effect of the degree of delignification on the LCC types during kraft pulping and during subsequent oxygen stage was studied in order to understand the role of LCC for the stability of residual lignin. For both processes, high delignification rates were observed for the xylan-rich LCC and cellulose-rich LCC fractions, whereas the glucomannan-rich LCC was relatively stable. After a severe oxygen stage, almost all the residual lignin was isolated in the latter complex.

Thioacidolysis in combination with gas chromatography was used to determine the content of β-O-4 structures in the lignin. Periodate oxidation and methanol determinations were used to quantify the phenolic hydroxyl groups, whereas size exclusion chromatography (SEC) of the thioacidolysis fractions was used to monitor any differences between the original molecular size distribution and that after the delignification processes. Major differences between the various LCC fractions were observed, clearly indicating that two different forms of lignin are present in the wood fibre wall. These forms are linked to glucomannan and xylan respectively. The xylan linked lignin was found to consist largely of β-O-4 structures indicating a rather linear coupling mode, whereas the glucomannan linked lignin was more heterogeneous with respect to the known lignin inter-unit linkage types. Based on these findings, a modified arrangement of the fibre wall polymers is suggested. From acid sulfite pulp (Kappa number 11) residual lignin was isolated at ~80% yield on LCC basis. About 60% was linked to xylan, 30% to glucomannan and 10% to glucans. These values differ greatly from those obtained for softwood pulped to a similar kappa number by the Kraft method. Model compound studies indicated that the benzyl ether type of LC linkage were likely to survive cleavage at the acidic sulfite pulping conditions

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 58 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2005:30
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-458 (URN)
Public defence
2005-10-28, STFI-salen, Drottning Kristinasväg 61, Stockholm, 10:00
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Supervisors
Note
QC 20101026Available from: 2005-10-20 Created: 2005-10-20 Last updated: 2010-10-26Bibliographically approved

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