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Deepening the insights of lignin structure: Lignin-carbohydrate complex (LCC) fractionation and characterization and Kraft lignin amination
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
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: urn:nbn:se:kth:diva-126279ISBN: 978-91-7501-818-8 (print)OAI: oai:DiVA.org:kth-126279DiVA: diva2:642070
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
List of papers
1. Universal fractionation of lignin-carbohydrate complexes (LCCs) from lignocellulosic biomass: an example using spruce wood
Open this publication in new window or tab >>Universal fractionation of lignin-carbohydrate complexes (LCCs) from lignocellulosic biomass: an example using spruce wood
2013 (English)In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 74, no 2, 328-338 p.Article in journal (Refereed) Published
Abstract [en]

It is of both theoretical and practical importance to develop a universally applicable approach for the fractionation and sensitive lignin characterization of lignin-carbohydrate complexes (LCCs) from all types of lignocellulosic biomass, both natively and after various types of processing. In the present study, a previously reported fractionation approach that is applicable for eucalyptus (hardwood) and flax (non-wood) was further improved by introducing an additional step of barium hydroxide precipitation to isolate the mannan-enriched LCC (glucomannan-lignin, GML), in order to suit softwood species as well. Spruce wood was used as the softwood sample. As indicated by the recovery yield and composition analysis, all of the lignin was recovered in three LCC fractions: a glucan-enriched fraction (glucan-lignin, GL), a mannan-enriched fraction (GML) and a xylan-enriched fraction (xylan-lignin, XL). All of the LCCs had high molecular masses and were insoluble or barely soluble in a dioxane/water solution. Carbohydrate and lignin signals were observed in H-1 NMR, C-13 CP-MAS NMR and normal- or high-sensitivity 2D HSQC NMR analyses. The carbohydrate and lignin constituents in each LCC fraction are therefore believed to be chemically bonded rather than physically mixed with one another. The three LCC fractions were found to be distinctly different from each other in terms of their lignin structures, as revealed by highly sensitive analyses by thioacidolysis-GC, thioacidolysis-SEC and pyrolysis-GC.

Keyword
lignin-carbohydrate complex (LCC), universal fractionation approach, spruce, NMR, thioacidolysis, pyrolysis-GC
National Category
Plant Biotechnology
Identifiers
urn:nbn:se:kth:diva-122524 (URN)10.1111/tpj.12124 (DOI)000317296200012 ()2-s2.0-84876293824 (Scopus ID)
Note

QC 20130524

Available from: 2013-05-24 Created: 2013-05-23 Last updated: 2017-12-06Bibliographically approved
2. Understanding Pulp Delignification by Laccase-Mediator Systems through Isolation and Characterization of Lignin-Carbohydrate Complexes
Open this publication in new window or tab >>Understanding Pulp Delignification by Laccase-Mediator Systems through Isolation and Characterization of Lignin-Carbohydrate Complexes
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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.

Keyword
eucalyptus pulp, delignification, laccase-mediator systems, lignin-carbohydrate complex (LCC), thioacidolysis, pyrolysis-GC/MS
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-126105 (URN)10.1021/bm4006936 (DOI)000330095500014 ()2-s2.0-84883826344 (Scopus ID)
Note

QC 20140214

Available from: 2013-08-19 Created: 2013-08-19 Last updated: 2017-12-06Bibliographically approved
3. Improvement of kraft pulp bleaching by treatments with laccase, urea, and refining
Open this publication in new window or tab >>Improvement of kraft pulp bleaching by treatments with laccase, urea, and refining
2013 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 67, no 6, 651-658 p.Article in journal (Refereed) Published
Abstract [en]

Unbleached Eucalyptus kraft pulps were treated by three methods and the bleaching effects have been evaluated. The treatments were performed by a laccase mediator system (LMS), refining (R), and urea (U) alone and in combination of these methods. The bleached pulps were characterized in terms of κ number, hexenuronic acid content, brightness, and viscosity. In addition, the lignin-carbohydrate complexes (LCCs) were fractionated and characterized with regard to the fractionation yield, lignin content, and carbohydrate composition. Moreover, the 1 H nuclear magnetic resonance spectra were recorded and the thioacidolysis-gas chromatography and thioacidolysis-size exclusion chromatography analyses were performed. The LMS treatment resulted mainly in a slightly better delignification as manifested by a κ number (K no.) reduction of 0.8 units. The effects of the U treatment included delignification (1.4 κ units), hexenuronic acid removal (3 μ mol g-1), and improved pulp brightness (3.4 ISO units). The R treatment darkened the pulp (3 ISO units), whereas the bleaching of the R-pulp by subsequent LMS or U treatment enhanced the brightness (0.5 unit more) or delignification (0.3 unit more). The residual lignin in the pulp samples was present mainly as xylan-lignin. The Klason lignin content from the xylan lignin fraction decreased as the degree of delignification increased. The pulp darkening followed by the R treatment was interpreted as the result of the formation of condensed lignin structures, but these condensed lignins were substantially removed by the subsequent LMS or U treatment.

Keyword
bleaching, Eucalyptus, laccase-mediator system, lignin-carbohydrate complex (LCC), refining, thioacidolysis, urea
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-126277 (URN)10.1515/hf-2012-0140 (DOI)000324719100005 ()2-s2.0-84904999585 (Scopus ID)
Note

QC 20131017

Available from: 2013-08-20 Created: 2013-08-20 Last updated: 2017-12-06Bibliographically approved
4. On hexenuronic acid (HexA) removal and mediator coupling to pulp fiber in the laccase/mediator treatment
Open this publication in new window or tab >>On hexenuronic acid (HexA) removal and mediator coupling to pulp fiber in the laccase/mediator treatment
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2011 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 102, no 4, 3911-3917 p.Article in journal (Refereed) Published
Abstract [en]

Flax soda/AQ pulps were treated with different fungal laccase-mediator combinations followed by physical and chemical characterization of the pulps to obtain a thorough understanding of the laccase/mediator effects on hexenuronic acid (HexA) removal and the coupling of mediator onto pulps for fiber functionalization. Large differences were found and the presence of lauryl gallate (LG) during Trametes villosa laccase (TvL) treatment (TvL + LG) resulted in a much larger reduction of pulp-linked HexA than the combination of p-coumaric acid (PCA) and Pycnoporus cinnabarinus laccase (PcL). A major portion of LG became attached to the pulp as revealed by an increase in the kappa number and further confirmed by thioacidolysis and H-1 NMR analysis of solubilized pulp fractions. Additional experiments with other chemical pulps and isolated pulp xylan and lignin revealed that HexA seems to be the sole pulp component attacked by TvL + LG. As a substrate for TvL, the reaction preference order is PCA > HexA > LG.

Keyword
Biobleaching, Coupling, Flax, Functionalization, Hexenuronic acid
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-31363 (URN)10.1016/j.biortech.2010.11.127 (DOI)000287277800036 ()2-s2.0-78651488677 (Scopus ID)
Note
QC 20110316Available from: 2011-03-16 Created: 2011-03-14 Last updated: 2017-12-11Bibliographically approved
5. Modification of industrial softwood kraft lignin using Mannich reaction with and without phenolation pretreatment
Open this publication in new window or tab >>Modification of industrial softwood kraft lignin using Mannich reaction with and without phenolation pretreatment
2014 (English)In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 52, 729-735 p.Article in journal (Refereed) Published
Abstract [en]

The amination of industrial softwood kraft lignin was conducted using the Mannich reaction to modify the lignin structure for value-added applications. To understand the reaction mechanism and to quantify the amount of amine groups that were introduced, different types of NMR analyses were performed. The lignin was also pretreated by phenolation to increase its reactivity and the amount of the amine groups that were introduced. The Mannich reaction was very selective at the C-5 position of the guaiacyl units and complete under acidic conditions with similar to 11-fold amounts of reagents of dimethylamine and formaldehyde over either model lignin (4-hydroxy-3-methoxyacetophenone, HMAP) or industrial spruce kraft lignin (LignoBoost lignin, LBL). For LBL, 28 amine groups were introduced over 100 aromatic rings. By weight, the nitrogen content was 2.5%. The animated lignin was found to possess a higher molecular mass, reaching a Mp of 4.9 x 10(3) Da compared to the original 319 x 10(3) Da, and with a considerably increased dispersibility, especially in a dilute aqueous solution of hydrochloric acid (pH = 3), namely 5.2 mg/ml. With a preceding phenolation treatment, which increased the amount of phenolic aromatic rings available for the Mannich reaction, an introduction of 42 amine groups over 100 aromatic rings, or a nitrogen content of 4.8%, was obtained, which caused a further increase of the molecular mass to 5.1 x 10(3) Da (Mp) and of dispersibility in the aqueous solution of hydrochloric acid up to 32.0 mg/ml. The aminated lignins with or without the phenolation pretreatment formed very stable colloidal suspensions in water, with large particle sizes (391 and 39 nm), high zeta potentials (31.6 and 27.2 mV), and large charge densities (1.6 and 1.2 x 10(-7) equiv./ml, respectively). The potential value-added applications of these modified lignins with high amine contents include use as surfactant chemicals, polycationic materials and slow-release fertilisers, among others.

Keyword
Amination, Colloidal properties, Dispersibility, NMR, Mannich reaction, Phenolation, Softwood kraft lignin
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-126271 (URN)10.1016/j.indcrop.2013.11.035 (DOI)000332189200097 ()2-s2.0-84890617812 (Scopus ID)
Note

QC 20140404. Updated from manuscript to article in journal.

Available from: 2013-08-20 Created: 2013-08-20 Last updated: 2017-12-06Bibliographically approved
6. Lignin-carbohydrate and lignin-lignin linkages in different lignin-carbohydrate complexes from spruce wood
Open this publication in new window or tab >>Lignin-carbohydrate and lignin-lignin linkages in different lignin-carbohydrate complexes from spruce wood
Show others...
(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
Lignin-carbohydrate complex (LCC), enzymatic hydrolysis, spruce, 2D HSQC, NMR, Pyrolysis-GC/MS
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-126274 (URN)
Note

QS 2013

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

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