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Understanding Pulp Delignification by Laccase-Mediator Systems through Isolation and Characterization of Lignin-Carbohydrate Complexes
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
Instituto de Recursos Naturales y Agrobiologia de Sevilla.
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2013 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 14, no 9, 3073-3080 p.Article in journal (Refereed) Published
Abstract [en]

The effects and mechanism of pulp delignificabon by laccases in the presence of redox mediators have been investigated on unbleached eucalyptus kraft pulp treated with laccases from Pycnoporus cinnabarinus (PcL) and Myceliophthora thermophila (MtL) and 1-hydroxybenzotriazole (HBT) and methyl syringate (MeS) as mediators, respectively. Determination of the corrected kappa number in eucalyptus pulps after the enzymatic treatments revealed that the PcL-HBT system exhibited a more remarkable delignification effect than the MtL-MeS system. To obtain further insight, lignin-carbohydrate complexes were fractionated and subsequently characterized by nuclear magnetic resonance, thioacidolysis (followed by gas chromatography and size exclusion chromatography), and pyrolysis-gas chromatography-mass spectrometry (pyrolysis-GC-MS) analyses before and after the enzymatic treatments and their controls. We can conclude that the laccase mediator treatments altered the lignin structures in such a way that more lignin was recovered in the xylan-lignin fractions, as shown by Klason lignin estimation, with smaller amounts of both syringyl (5) and guaiacyl (G) uncondensed units, as shown by thioacidolysis and gas chromatography, especially after the PcL-HBT treatment. The laccase mediator treatment produced oxidation at C alpha and cleavage of C alpha and C beta bonds in pulp lignin, as shown by pyrolysis-GC-MS. The general mechanism of residual lignin degradation in the pulp by laccase-mediator treatments is discussed in light of the results obtained.

Place, publisher, year, edition, pages
2013. Vol. 14, no 9, 3073-3080 p.
Keyword [en]
eucalyptus pulp, delignification, laccase-mediator systems, lignin-carbohydrate complex (LCC), thioacidolysis, pyrolysis-GC/MS
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-126105DOI: 10.1021/bm4006936ISI: 000330095500014Scopus ID: 2-s2.0-84883826344OAI: oai:DiVA.org:kth-126105DiVA: diva2:641880
Note

QC 20140214

Available from: 2013-08-19 Created: 2013-08-19 Last updated: 2017-12-06Bibliographically 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)
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Supervisors
Note

QC 20130820

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

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