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Structural differences between the lignin-carbohydrate complexes present in wood and in chemical pulps
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-8614-6291
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2005 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 6, 3467-3473 p.Article in journal (Refereed) Published
Abstract [en]

Lignin-carbohydrate complexes (LCCs) were prepared in quantitative yield from spruce wood and from the corresponding kraft and oxygen-delignified pulps and were separated into different fractions on the basis of their carbohydrate composition. To obtain an understanding of the differences in lignin structure and reactivity within the various LCC fractions, thioacidolysis in combination with gas chromatography was used to quantify the content of β-O-4 structures in the lignin. Periodate oxidation followed by determination of methanol was used to quantify the phenolic hydroxyl groups. Furthermore, 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. Characteristic differences between the various LCC fractions were observed, clearly indicating that two different forms of lignin are present in the wood fiber wall. These forms are linked to glucomannan and xylan, respectively. On pulping, the different LCCs have different reactivities. The xylan-linked lignin is to a large extent degraded, whereas the glucomannan-linked lignin undergoes a partial condensation to form more high molecular mass material. The latter seems to be rather unchanged during a subsequent oxygen-delignification stage. On the basis of these findings, a modified arrangement of the fiber wall polymers is suggested.

Place, publisher, year, edition, pages
2005. Vol. 6, no 6, 3467-3473 p.
Keyword [en]
SOFTWOOD KRAFT PULP, RESIDUAL LIGNIN, SPRUCE LIGNIN, THIOACIDOLYSIS, CONDENSATION, COOKING, BONDS
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-7822DOI: 10.1021/bm058014qISI: 000233392100077Scopus ID: 2-s2.0-28844493617OAI: oai:DiVA.org:kth-7822DiVA: diva2:12958
Note
QC 20100930. Uppdaterad från Submitted till Published (20100930).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
Opponent
Supervisors
Note
QC 20101026Available from: 2005-10-20 Created: 2005-10-20 Last updated: 2010-10-26Bibliographically approved

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