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Lignin-carbohydrate and lignin-lignin linkages in different lignin-carbohydrate complexes from spruce wood
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
Centro de Investigaciones Biologicas.
Instituto de Recursos Naturales y Agrobiologia de Sevilla.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

In order to characterize lignin-carbohydrate (LC) and lignin-lignin (LL) linkages in different lignin-carbohydrate complexes (LCCs), the glucan-lignin (GL), glucomannan-lignin (GML) and xylan-lignin (XL) isolated from spruce wood have been enzymatically hydrolyzed, using endoglucanase plus b-glucosidase (for GL and GML) or xylanase (for XL), followed by 2D HSQC NMR and Py-GC/MS analysis. It has been found that the enzymatic hydrolysis removed effectively most of the polysaccharide parts in the LCCs and thus enriched the lignin contents and LCC linkages so that various LC and LL linkages could be well demonstrated by the 2D HSQC NMR analysis. Three typical LC linkages, i.e. benzyl ether, γ-ester and phenyl glycoside, have been directly observed in the enzymatically hydrolyzed GML (En-GML) and enzymatically hydrolyzed XL (En-XL). There are two types of benzyl ether linkages, with primary and secondary OH from carbohydrates. There are three types of carbohydrate units linked with lignin by the phenyl glycoside bonds in the En-GML while only one type is found in the En-XL. It seems that mannose and galactose are among the sugar units involved in the linkages since their relative amounts in the sugar compositions increased after the enzymatic hydrolysis. From the LL linkages observed in the 2D HSQC NMR spectra, it was revealed that the lignin existing in GML is less condensed than the lignin from XL due to a higher percentage of β-O-4 sub-structure found in the former (75 % vs. 66 %). On the other hand, more other substructures have been found present in the lignin from XL than GML, e.g. phenylcoumaran (17 % vs. 15 %), dibenzodioxocin (9 % vs. 5 %), resinol (11 % vs. 6 %), and spirodienone (2 % vs. 1 %), implying more condensed lignin structures present in the XL. From the Py-GC/MS analysis, the relative amounts of guaiacol and coniferyl alcohol fragments over the acetoguaiacone fragment, an internal marker, were largely increased after the enzymatic hydrolysis, supporting the presences of even higher amounts of the phenyl glucoside LC linkages in the original LCCs since some of the linkages should have been cleaved during the enzymatic hydrolysis. The NMR analysis of the En-GL was not successful probably due to the attachment of the enzymes onto the GL structure or the existence of the remained crystalline cellulose structures.

Keyword [en]
Lignin-carbohydrate complex (LCC), enzymatic hydrolysis, spruce, 2D HSQC, NMR, Pyrolysis-GC/MS
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-126274OAI: oai:DiVA.org:kth-126274DiVA: diva2:642022
Note

QS 2013

Available from: 2013-08-20 Created: 2013-08-20 Last updated: 2013-08-20Bibliographically approved
In thesis
1. Deepening the insights of lignin structure: Lignin-carbohydrate complex (LCC) fractionation and characterization and Kraft lignin amination
Open this publication in new window or tab >>Deepening the insights of lignin structure: Lignin-carbohydrate complex (LCC) fractionation and characterization and Kraft lignin amination
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Improvement of kraft pulping delignification efficiency and value-addition of industrial kraft lignin are two attractive topics. The proposal that delignification is deteriorated by the presence of lignin-carbohydrate complex (LCC) is still being debated. Therefore, it is theoretically and practically important to investigate various LCC structures from native wood and their changes during different treatments. Currently, however, there is no effective LCC fractionation method that could quantitatively isolate all LCC fractions and be applicable for all types of lignocellulosic materials. The fractionation should also be followed by comprehensive and reliable structural characterisation. Additionally the Kraft lignin has a heterogeneous structure and poor properties. Structural modification is therefore one possible solution for creating more economical benefits than the presently direct combustion for heat.

In this work, an LCC fractionation method has been developed, which preserves original lignin and lignin-carbohydrate (LC) bonding structures and is nearly quantitative. It is universally applicable for hardwood, softwood or non-wood species. A whole set of subsequent analytical tools for the comprehensive elucidation of the different LCC fractions has also been established and applied. After applying the LCC fractionation and characterisation:

1). spruce wood was found to consist of 49.5% glucan-lignin (GL), 30.9% glucomannan–lignin (GML) and 12.0% xylan–lignin (XL). Although the LC and lignin-lignin (LL) linkage signals could not be directly observed by a 400 MHz NMR instrument, these linkages have been clearly observed by a 600 MHz NMR instrument equipped with a cryogenic probe after enzymatic hydrolysis. The LC bondings include phenyl glycoside, benzyl ether and γ-ester. Based on the LL bond frequencies, GML is less condensed than XL.

2). a general lignin biodegradation mechanism by the laccase-mediator system (LMS) has been proposed, which mainly involves Cα oxidation and Cα-Cβ bond cleavage of the lignin side chain and eventually aromatic ring cleavage. The LMS delignification efficiency depends largely on the species of the applied laccase and mediator. Some LMS has been proven to possess an obvious capacity for hexenuronic acid (HexA) removal. For Kraft pulp bleaching, there are potential benefits of various combinations among biological treatment (by LMS), non-oxidative chemical (by urea treatment, U), and mechanical treatment (by refining, R).

In addition, it has been demonstrated in this work that the structures and properties of industrial softwood Kraft lignin (LignoBoost lignin) could largely be upgraded by amination via the Mannich reaction. With or without a phenolation pretreatment, the aminated lignins obtained are promising polycationic materials, especially in the application as colloidal suspensions. During this investigation of kraft lignin amination, NMR methods have been developed for the quantification of the N content introduced and for the deepened insights of the structural changes of the lignin. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 65 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:30
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-126279 (URN)978-91-7501-818-8 (ISBN)
Public defence
2013-09-10, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130820

Available from: 2013-08-20 Created: 2013-08-20 Last updated: 2013-08-20Bibliographically approved

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