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Structural Modifications of Lignosulphonates
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
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: urn:nbn:se:kth:diva-32881ISBN: 978-91-7415-923-3OAI: oai:DiVA.org:kth-32881DiVA: diva2:412703
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
List of papers
1. Oxidative polymerisation of models for phenolic lignin end-groups by laccase
Open this publication in new window or tab >>Oxidative polymerisation of models for phenolic lignin end-groups by laccase
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2010 (English)In: Holzforschung, ISSN 0018-3830, Vol. 64, no 1, 21-34 p.Article in journal (Refereed) Published
Abstract [en]

The redox enzyme laccase can lead to cross-linking of lignin molecules by oxidising phenolic end groups to resonance-stabilised radicals that can undergo radical coupling to form covalent bonds. This property has potential for many technical applications. However, laccase treatment can also lead to degradation. Experiments were performed with two laccases of different oxidation potential and pH and temperature optima. The predominant reaction following laccase oxidation is the formation of 5-5' and 4-O-5' bonds. If the 5-position is blocked, other reactions occur, including coupling of the 1-position and oxidation of the a-position, which aggravates cross-linking of different lignin molecules. The product profile generated by the two laccases is somewhat different, mainly because of the different pH rather than differences in enzyme activity. Reaction mechanisms and the technical and biological significance of the results are discussed.

Keyword
biotechnology, laccase, lignin, lignin model compound, lignin, polymerisation, phenolic end group, reaction mechanism, flight mass-spectrometry, kraft pulp, mediator, delignification, degradation, quinones, polymers, oxidase, oxygen, ms
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-19138 (URN)10.1515/hf.2010.001 (DOI)000273912800004 ()2-s2.0-74049119347 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2012-03-22Bibliographically approved
2. Sulfonation of phenolic end groups in lignin directs laccase-initiated reactions towards cross-linking
Open this publication in new window or tab >>Sulfonation of phenolic end groups in lignin directs laccase-initiated reactions towards cross-linking
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2010 (English)In: Industrial Biotechnology, 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.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-33276 (URN)10.1089/ind.2010.6.050 (DOI)2-s2.0-77649262194 (ScopusID)
Note
QC 20110501Available from: 2011-05-02 Created: 2011-05-02 Last updated: 2012-03-22Bibliographically approved
3. Investigation of the Molecular Weight Increase of Commercial Lignosulfonates by Laccase Catalysis
Open this publication in new window or tab >>Investigation of the Molecular Weight Increase of Commercial Lignosulfonates by Laccase Catalysis
2010 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 4, 904-910 p.Article in journal (Refereed) Published
Abstract [en]

Lignosulfonates are by-products from the sulfite pulping process. During this process, lignin is liberated from pulp fibers through sulfonation and washed away. As a consequence, the lignosulfonate molecules contain both hydrophobic and hydrophilic moieties. Lignosulfonates are low-value products with limited performance and are used as such as binders, surfactants, and plasticizers in concrete. Lignosulfonates face strong competition from synthetic petroleum-based plasticizers with superior quality. Therefore, increasing the performance of lignosulfonates is desirable not only from a sustainability point of view but also to expand their usage. One important aspect that describes how well lignosulfonates can act as plasticizers is the molecular weight. In this paper, the molecular weight of four commercial lignosulfonates is increased through oxidation by two laccases without utilization of mediators. Different parameters to obtain maximal molecular weight increase were identified and the technical significance of the experiments is discussed.

Keyword
spruce wood, lignin, delignification, biosynthesis, oxidation, model, pulp
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-19391 (URN)10.1021/bm901258v (DOI)000276557300010 ()2-s2.0-77950824209 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-05-02Bibliographically approved
4. Structural modification of commercial lignosulphonates through laccase catalysis and ozonolysis
Open this publication in new window or tab >>Structural modification of commercial lignosulphonates through laccase catalysis and ozonolysis
2010 (English)In: Industrial crops and products (Print), ISSN 0926-6690, Vol. 32, no 3, 458-466 p.Article in journal (Refereed) Published
Abstract [en]

Lignosulphonates are by-products from the sulphite pulping process, in which lignin is separated from cellulose by the addition of sulphonic acid groups to the alpha-position of lignin, thereby increasing the solubility of lignin in water. The predominant industrial utilisations of lignosulphonates are as dispersants, plasticisers and water-reducing agents in concrete preparation. The ability of lignosulphonates to function as a good plasticisers and water reducers is intimately linked with the purity of the lignosulphonate, its molecular weight and the number of charged groups present in the macromolecule. Currently, lignosulphonates are outrivaled by synthetic plasticisers termed superplasticisers due to their superior properties when used as additives to high-strength concrete. If lignosulphonates are to successfully compete with these superplasticisers, significant modifications are required. This paper describes a two-stage treatment of lignosulphonates in which the molecular weight is increased through laccase oxidation and carboxylic groups are introduced through ozonolysis. The technical significance of the results is also discussed.

Keyword
Lignosulphonates, Biotechnology, Plasticisers, Concrete, Cement, Laccase, Ozonolysis, Molecular weight, Carboxylic acids
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-27083 (URN)10.1016/j.indcrop.2010.06.016 (DOI)000283962300042 ()2-s2.0-77957243430 (ScopusID)
Note
QC 20101210Available from: 2010-12-10 Created: 2010-12-06 Last updated: 2011-05-02Bibliographically approved
5. Immobilisation of laccase for polymerisation of commercial lignosulphonates
Open this publication in new window or tab >>Immobilisation of laccase for polymerisation of commercial lignosulphonates
2011 (English)In: Process Biochemistry, ISSN 1359-5113, E-ISSN 1873-3298, Vol. 46, no 5, 1071-1075 p.Article in journal (Refereed) Published
Abstract [en]

The oxidoreductive enzyme laccase has previously been shown to be able to increase the average molecular weight of lignosulphonatesthrough generation of phenoxy radicals on end groups and the subsequent radical-radical coupling reactions that cross-link individual lignosulphonate molecules. Utilisation of laccases for this purpose is a potential industrial process not only to improve the properties of technical lignosulphonates but also to expand their utilisation to new areas. Immobilisation of the laccase is an interesting technique to enable reusage of the enzyme and thus reduce costs involved with such process. In this work, we demonstrate the potential of immobilised laccase to polymerise technical lignosulphonates. A number of factors that limits re-utilisation of the immobilised catalyst such as lignosulphonate adsorption onto the carrier and laccase deactivation have been identified and are discussed. However, by using a low-porosity support and lower reaction temperatures these problems can be limited.

Keyword
Biotechnology, GLUTAL/APTES, Immobilisation, Laccase, Lignosulphonates, Molecular weight
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-33277 (URN)10.1016/j.procbio.2011.01.024 (DOI)000290466800005 ()2-s2.0-79953174198 (ScopusID)
Funder
EU, European Research Council, FP6-NMP2-CT 2006-26456
Note
QC 20110501Available from: 2011-05-02 Created: 2011-05-02 Last updated: 2011-06-08Bibliographically approved
6. Fenton's reaction: a simple and versatile method to structurally modify commercial lignosulphonates
Open this publication in new window or tab >>Fenton's reaction: a simple and versatile method to structurally modify commercial lignosulphonates
2011 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 26, no 1, 90-98 p.Article in journal (Refereed) Published
Abstract [en]

Treatment of lignosulphonates with hydrogen peroxide and Fe (II) acetate under mild conditions can be used to increase the molecular weight and content of carboxylic acids. Such Fenton's oxidation can produce, in some of the conditions of and lignosulphonate concentration, a two-fold increase in the molecular weight and a 6-7 fold increase in the carboxylic acid content. The structural modifications of lignosulphonate may increase the technical performance of the product in several applications. Possible reaction mechanisms of the Fenton system are proposed and discussed.

Keyword
Lignosulphonate, Fenton's reagent, Molecular weight increase, Carboxylic groups, Phenolic groups, Structural modifications, Reaction mechanism, Hydrogen peroxide
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-38866 (URN)10.3183/NPPRJ-2011-26-01-p090-098 (DOI)000293770200009 ()2-s2.0-79955452061 (ScopusID)
Note
QC 20110901Available from: 2011-09-01 Created: 2011-09-01 Last updated: 2011-09-01Bibliographically approved

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