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Sulfonation of phenolic end groups in lignin directs laccase-initiated reactions towards cross-linking
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
University of Helsinki, Department of Chemistry.
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.
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2010 (English)In: Industrial Biotechnology, ISSN 1550-9087, E-ISSN 1931-8421, Vol. 6, no 1, 50-59 p.Article in journal (Refereed) Published
Abstract [en]

The effect of sulfonation of the a-carbon on model compounds representing phenolic end groups on lignin was studied with respect to the reactions initiated by oxidation of laccase, by mass spectrometry. Sulfonation seems to direct the reactions towards formation of 5-5´ and 4-O-5´ bonds, avoiding formation of 1-O-4´ bonds and oxidation of the a-carbon. This, in turn, will facilitate cross-linking reactions between lignin molecules. Sulfonation therefore has potential as an industrial pretreatment prior to laccase treatment for various wood-containing materials.

Place, publisher, year, edition, pages
2010. Vol. 6, no 1, 50-59 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-33276DOI: 10.1089/ind.2010.6.050Scopus ID: 2-s2.0-77649262194OAI: oai:DiVA.org:kth-33276DiVA: diva2:414031
Note

QC 20110501

Available from: 2011-05-02 Created: 2011-05-02 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Structural Modifications of Lignosulphonates
Open this publication in new window or tab >>Structural Modifications of Lignosulphonates
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lignosulphonates are by‐products from the sulphite pulping process for the manufacture ofspecialty dissolving pulps and paper. During the liberation of the cellulose, the lignin isfractionated and solubilised through covalent addition of sulphonic acid groups at variouspositions in the structure. The formed sulphonated lignin, lignosulphonate is then furtherisolated and refined.

The amphiphilic nature of lignosulphonates has enabled them to be used as additives to varioussuspensions to improve their dispersion and stability. The by far largest utilisation oflignosulphonates is as dispersants in concrete. Here, lignosulphonates act by dispersing cementparticles to prevent flocculation, un‐even particle distribution and reduced strengthdevelopment. The dispersion is achieved through steric and electrostatic repulsion of the cementparticles by the lignosulphonate polymer. This behaviour is intimately linked with the overallsize and amount of charged groups in the dispersing polymer. Traditional modifications oflignosulphonates have been limited to removal of sugars, filtration and fractionation. Thesemodifications are not sufficient for utilisation of lignosulphonates in high‐strength concrete. Heresynthetic dispersants and superplasticisers are used which are considerably more efficient evenat low dosages. To compete with these, additional modifications of lignosulphonates are likely tobe necessary. The molecular weight and functional group composition have been identified anddescribed as the most interesting parameters that can be modified.

Currently, no suitable method exists to increase the molecular weight of lignosulphonates.Oxidation by the natural radical initiating enzyme laccase is an interesting tool to achieve suchmodifications. In this thesis several aspects of the mechanism through which this enzyme reactswith lignin and lignosulphonate structures have been elucidated through model compoundstudies. Further studies showed that laccase alone was a highly efficient tool for increasing themolecular weight of commercial lignosulphonates at low dosages and in short incubation times.Immobilisation of the laccase to a solid support to enable re‐utilisation was also investigated.

Modification of functional group composition of lignosulphonates was achieved throughozonolysis and the Fenton’s reagent, a mixture of hydrogen peroxide and iron(II)acetate.Introduction of charged carboxylic groups was achieved through opening of the benzyl rings oflignosulphonates. It was found that a two‐stage process consisting of laccase oxidation followedby ozonolysis was an efficient technique to create a polymer enriched with carboxylic acidgroups with a sufficient molecular size.

Oxidation by the Fenton’s reagent was shown to yield similar modifications as the combinedlaccase/ozonolysis treatment albeit with less pronounced results but with a large level of controlthrough variation of a number of reaction parameters. The Fenton’s reagent can therefore be aninteresting alternative to the aforementioned two‐stage treatment.

These modifications are interesting for large‐scale applications not only because of theirsimplicity in terms of reaction parameters but also because of the ubiquity of the used enzymeand the chemicals in the pulp and paper industry.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 55 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:26
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-32881 (URN)978-91-7415-923-3 (ISBN)
Public defence
2011-05-13, D3, Lindstedsvägen 3, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110427Available from: 2011-04-27 Created: 2011-04-26 Last updated: 2011-09-01Bibliographically approved

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