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Lignin polysaccharide networks in softwood and chemical pulps: characterisation, structure and reactivity
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-8614-6291
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: urn:nbn:se:kth:diva-458OAI: oai:DiVA.org:kth-458DiVA: diva2:12959
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
List of papers
1. New method for the quantitative preparation of lignin-carbohydrate complex from unbleached softwood kraft pulp: Lignin-polysaccharide networks I
Open this publication in new window or tab >>New method for the quantitative preparation of lignin-carbohydrate complex from unbleached softwood kraft pulp: Lignin-polysaccharide networks I
2003 (English)In: Holzforschung, ISSN 0018-3830, Vol. 57, no 1, 69-74 p.Article in journal (Refereed) Published
Abstract [en]

A new method for the quantitative preparation of pulp representative lignin-carbohydrate complexes (LCC) has been developed, in which LCC has been systematically prepared at quantitative yield, fractionated and qualitatively determined. At least 90% of residual lignin in softwood kraft pulp is proposed to be chemically bonded to carbohydrates. A major part of LCC (92%) in softwood kraft pulp was observed between lignin, xylan and glucomannan, whereas a minor part (8%) was linked to cellulose. Half of the hemicelullosic LCC is a lignin-glucomannan complex. The other half is lignin-xylan complex and xylan-lignin-glucomannan complex. Thus, part of the residual lignin in softwood kraft pulp crosslinks xylan and glucomannan. The proposed linkages are of covalent type. At most 10% of the residual lignin is not bonded covalently to carbohydrates.

Keyword
Endoglucanase, Lignin-carbohydrate complex (LCC), Residual lignin
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-7817 (URN)10.1515/HF.2003.011 (DOI)000181276300011 ()
Note
QC 20100923Available from: 2005-10-20 Created: 2005-10-20 Last updated: 2012-01-31Bibliographically approved
2. Changes in the lignincarbohydrate complex in softwood kraft pulp during kraft and oxygen delignification
Open this publication in new window or tab >>Changes in the lignincarbohydrate complex in softwood kraft pulp during kraft and oxygen delignification
Show others...
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.

Keyword
bleachability, kappa number, kraft pulping, lignin-carbohydrate complex (LCC), oxygen delignification, residual lignin, specific absorptivity
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-7818 (URN)10.1515/HF.2004.114 (DOI)000224277300005 ()2-s2.0-8344282690 (Scopus ID)
Note

QC 20150727

Available from: 2005-10-20 Created: 2005-10-20 Last updated: 2015-07-27Bibliographically approved
3. Characterization of Lignin-Carbohydrate Complexes from Spruce Sulfite Pulp: Lignin-polysaccharide networks III
Open this publication in new window or tab >>Characterization of Lignin-Carbohydrate Complexes from Spruce Sulfite Pulp: Lignin-polysaccharide networks III
2006 (English)In: Holzforschung, ISSN 0018-3830, Vol. 60, no 2, 162-165 p.Article in journal (Refereed) Published
Abstract [en]

Lignin-carbohydrate complexes (LCCs) were isolated from unbleached acid sulfite pulp by selective enzymatic hydrolysis followed by fiber swelling and extraction. Approximately 80% of the lignin in the pulp was found to be chemically linked to carbohydrates in three major fractions, viz. as one glucan-lignin complex (with 8% lignin) and two hemicellulose-lignin complexes (with 72% lignin). The latter two were further separated into one glucomannan-lignin complex (with similar to 25% lignin) and one xylan-lignin-glucomannan complex (with 45 - 50% lignin). Based on model experiments, it can be concluded that the lignin and carbohydrate moieties are probably linked together through benzyl ether linkages. Xylan is more stable towards acidic hydrolysis than galactoglucomannan, and this finding may explain the greater amount of xylan-rich LCC in the pulp.

Keyword
acid sulfite pulp, glucomannan, lignin-carbohydrate complex (LCC), phenyl glucoside, xylan
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-7819 (URN)10.1515/HF.2006.026 (DOI)000236203100008 ()
Note
Uppdaterad från submitted till published: 20101026. QC 20101026Available from: 2005-10-20 Created: 2005-10-20 Last updated: 2010-10-26Bibliographically approved
4. Characterisation of lignin-carbohydrate complexes (LCCs) of spruce wood (Picea abies L.) isolated with two methods.
Open this publication in new window or tab >>Characterisation of lignin-carbohydrate complexes (LCCs) of spruce wood (Picea abies L.) isolated with two methods.
2006 (English)In: Holzforschung, ISSN 0018-3830, Vol. 60, no 2, 151-161 p.Article in journal (Refereed) Published
Abstract [en]

A method for the quantitative isolation of lignin-carbohydrate complexes (LCCs) in a softwood is presented. The isolation steps involve partial enzymatic hydrolysis of cellulose, subsequent swelling in urea, and quantitative dissolution into four major fractions: (1) a galacto-glucomannan LCC containing similar to 8% of the wood lignin; (2) a glucane LCC containing similar to 4% of the wood lignin; (3) a xylan-lignin-glucomannan network LCC (xylan > glucomannan) containing similar to 40% of the wood lignin; and (4) a glucomannan-lignin-xylan network LCC (glucomannan) xylan) containing similar to 48% of the wood lignin. Endo-glucanase Novozyme 476, with only cellulase activity, and Ecopulp XM, with only xylanase and mannanase activities, were used as an enzymatic tool. From mildly ball-milled wood, all the lignin was isolated as LCCs. As a control, LCC was prepared from partially chlorite-delignified wood meal without ball milling, also in a mild procedure. The results were very similar to those obtained after ball milling. Thus, it can be safely concluded that the formation of new chemical linkages between lignin and carbohydrates during ball milling is improbable. Studies on isolated milled wood lignin (MWL) supported this conclusion and clearly showed that covalent linkages between lignin and carbohydrates are present. The study provide conclusive evidence of covalent linkages between lignin and carbohydrates in the native lignin in wood. It is concluded that carbohydrate-free lignin, i.e., lignin without covalent bonds to carbohydrates, probably cannot be present in spruce wood.

Keyword
endoglucanase, lignin carbohydrate complex (LCC), milled wood lignin (MWL), size exclusion chromatography (SEC)
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-7820 (URN)10.1515/HF.2006.025, 01/03/2006 (DOI)000236203100007 ()2-s2.0-33644926164 (Scopus ID)
Note
Tidigare titel: Characterisation of Lignin Carbohydrate Complexes (LCCs) in Softwood. Uppdaterad från submitted till published. QC 20101026 Available from: 2005-10-20 Created: 2005-10-20 Last updated: 2010-10-26Bibliographically approved
5. Analysis of Phenylglycosidic bonds
Open this publication in new window or tab >>Analysis of Phenylglycosidic bonds
(English)Manuscript (Other academic)
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-7821 (URN)
Note
QC 20101026Available from: 2005-10-20 Created: 2005-10-20 Last updated: 2010-10-26Bibliographically approved
6. Structural differences between the lignin-carbohydrate complexes present in wood and in chemical pulps
Open this publication in new window or tab >>Structural differences between the lignin-carbohydrate complexes present in wood and in chemical pulps
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.

Keyword
SOFTWOOD KRAFT PULP, RESIDUAL LIGNIN, SPRUCE LIGNIN, THIOACIDOLYSIS, CONDENSATION, COOKING, BONDS
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-7822 (URN)10.1021/bm058014q (DOI)000233392100077 ()2-s2.0-28844493617 (Scopus ID)
Note
QC 20100930. Uppdaterad från Submitted till Published (20100930).Available from: 2005-10-20 Created: 2005-10-20 Last updated: 2010-09-30Bibliographically approved

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