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Demethylation and other modifications of industrial softwood kraft lignin by laccase-mediators
KTH, School of Chemical Science and Engineering (CHE). (Fiber and Polymer Department)
(English)In: Article in journal (Refereed) Submitted
Abstract [en]

The lignin substitution of phenol in phenol-formaldehyde resin preparations is challenged by lignin’s inherently lower reactivity than phenol’s. Lignin demethylation by laccase treatment has been suggested to increase lignin’s reactivity, but no systematic study has been conducted on the obtained lignin structures and their dependence on the use of different mediators with laccase. In this study, one industrial softwood kraft lignin was treated with two commercial laccases, NS51002 (L1) and NS51003 (L2), in combination with three mediators, 2,2’-azino-bis-(3-ethyl-benzothiazoline)-6-sulfonate (ABTS), 1-hydroxybenzotriazole (HBT), and 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), and the resultant modified lignin structures were comprehensively characterized. It was found that regardless of the laccase and mediator used, methanol was released from the reaction solution, which was accompanied by a decrease in the number of methoxyl groups per aromatic ring. However, the formed catechol structure was further oxidized to a quinone structure, which polymerized, causing various increases in the molecular mass depending on the laccase-mediator combination used. In contrast, the -O-4´connection was cleaved to various extents, implying lignin depolymerization. Lignin demethylation was a common result from laccase treatment, but the reaction efficiency depended on the laccase and mediator used. The L1-ABTS, L1-TEMPO and L2-HBT combinations were the most efficient at modifying lignin to replace phenol in formaldehyde resins because they gave the highest reductions in methoxyl content. However, subsequent polymerization was observed, especially for L1-ABTS, which might have inhibited the reactivity of the treated lignin, although this needs further investigation.

National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-214042OAI: oai:DiVA.org:kth-214042DiVA, id: diva2:1139935
Note

QC 20170911

Available from: 2017-09-10 Created: 2017-09-10 Last updated: 2017-09-11Bibliographically approved
In thesis
1. Physical, Chemical and Biochemical Modifications of Industrial Softwood Kraft Lignin for Different Applications
Open this publication in new window or tab >>Physical, Chemical and Biochemical Modifications of Industrial Softwood Kraft Lignin for Different Applications
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Various technical lignins, e.g. industrial Softwood Kraft lignin (SKL), are now largely available while they are generally underutilized due to their heterogeneous and complicated structures and/or the poor properties. SKL has here been modified by physical, chemical and biochemical methods for preparation of lignin microspheres, phenol substitution in phenol-formaldehyde (PF) resin preparation and preparation of highly efficient fertilizers.

Physically, a brand-new slow and exhaustive solution evaporation process was developed for the highly efficient and productive preparation of microsphere structures. Highly homogenous SKL hollow microspheres were obtained and for the first time, urea encapsulating SKL microspheres were similarly prepared which could be an excellent controlled release urea fertilizer.

Chemically, Mannich reaction (one type of amination) was deeply investigated by including for the first time an LC-MS study of vanillin reaction, resulting in the establishment of a fast and reliable lignin reactivity (for phenol substation in PF resin) quantification method. In addition, SKL was functionalized using the Mannich reaction or esterification, leading to an improved hydrophobicity and compatibility for blending with polylactic acid (PLA). Using dip-coating technique for the first time, PLA-functionalised SKL-coated urea pellets were prepared, leading expectedly to a highly efficient urea fertilizer with simultaneous controlled- and slow- release and biological stabilization effects.

Biochemically, SKL was demethylated via incubation with different laccase-mediator combinations, which in principle will increase its reactivity in PF resin preparation. However, polymerization occurred which would decrease the reactivity.  The overall effects need to be further investigated.

Conclusively, broader or larger scale SKL applications can expectedly be realized after the development of SKL modifications tailored towards the optimum desired structures and properties.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. p. 83
Series
TRITA-CHE Report 2017:34, ISSN 1654-1081
National Category
Polymer Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-213985 (URN)978-91-7729-492-4 (ISBN)
Public defence
2017-09-18, Kollegiesalen F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 170912

Available from: 2017-09-12 Created: 2017-09-07 Last updated: 2017-10-05Bibliographically approved

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Wang, Miao

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