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Tailoring the Molecular and Thermo-Mechanical Properties of Kraft Lignin by Ultrafiltration
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), Centres, Wallenberg Wood Science Center.
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), Centres, Wallenberg Wood Science Center.
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2014 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 131, no 18, 9505-9515 p.Article in journal (Refereed) Published
Abstract [en]

This study has shown that ultrafiltration allows the selective extraction from industrial black liquors of lignin fraction with specific thermo-mechanical properties, which can be matched to the intended end uses. Ultrafiltration resulted in the efficient fractionation of kraft lignin according to its molecular weight, with an accumulation of sulfur-containing compounds in the low-molecular weight fractions. The obtained lignin samples had a varying quantities of functional groups, which correlated with their molecular weight with decreased molecular size, the lignin fractions had a higher amount of phenolic hydroxyl groups and fewer aliphatic hydroxyl groups. Depending on the molecular weight, glass-transition temperatures (T-g) between 70 and 170 degrees C were obtained for lignin samples isolated from the same batch of black liquor, a tendency confirmed by two independent methods, DSC, and dynamic rheology (DMA). The Fox-Flory equation adequately described the relationship between the number average molecular masses (M-n) and T-g's-irrespective of the method applied. DMA showed that low-molecular-weight lignin exhibits a good flow behavior as well as high-temperature crosslinking capability. Unfractionated and high molecular weight lignin (M-w > 5 kDa), on the other hand, do not soften sufficiently and may require additional modifications for use in thermal processings where melt-flow is required as the first step.

Place, publisher, year, edition, pages
2014. Vol. 131, no 18, 9505-9515 p.
Keyword [en]
biopolymers and renewable polymers, crosslinking, glass transition, rheology, thermal properties
National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-143949DOI: 10.1002/app.40799ISI: 000337623600057Scopus ID: 2-s2.0-84902544032OAI: oai:DiVA.org:kth-143949DiVA: diva2:709862
Note

QC 20140806. Updated from manuscript to article in journal.

Available from: 2014-04-03 Created: 2014-04-03 Last updated: 2017-12-05Bibliographically approved
In thesis
1. The Use of Membrane Filtration to Improve the Properties of Extracted Wood Components
Open this publication in new window or tab >>The Use of Membrane Filtration to Improve the Properties of Extracted Wood Components
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The forest is alarge and important natural resourcein Sweden, and approximately 70% of the country’s land area is woodland. Wood is an excellent raw material for the replacement of oil-based products because it is renewable, biodegradable and carbon neutral. Furthermore, the forest industry is searching for new processes and methods to utilise by-product streams in a so-called integrated biorefinery. A key to the success of producing new products from wood could be pure and homogenous raw materials. Because wood contains a large variety of components with different characteristics and sizes, cross-flow filtration (CFF) will be a key separation technique to obtain homogenous and pure raw materials in the biorefinery concept.

Different wood material components have been studied in this thesis. The first part of this work focuses on kraft lignin. Kraft lignin is interesting because approximately 3.5-4 million metric tonnes are produced in Sweden annually (~7million tonnes of kraft pulp/year in 2012), and today it is mainly used as fuel. The second part of this thesis deals with materials in hot water extract (i.e.,  galactoglucomannan, but also other components). These extracted materials are interesting because similar materials are extracted in thermomechanical pulping process by-product streams. Finally, nanocellulose has been studied since it is an interesting raw material for future applications.

Through CFF, kraft lignin from black liquor has been fractionated into raw material samples with more homogeneous characteristics such as molecular weight, aromatic hydroxyl groups and thermal properties. From dynamic mechanical analysis, low molecular weight fractions were found to have the highest degree softening. To precipitate low molecular weight fractions (<1000 Dacut-off) into a convenient solid, lower temperatures than forhigh molecular weight fractions were needed. To produce low molecular weight lignin (<5000 Da cut-off) from re-dissolved LignoBoost lignin, lower lignin concentrations and higher pH and ionic strength were found to increase the permeate fluxat the tested conditions.

Nanocellulose has been producedby a novel process called nanopulping and has subsequently been size fractionated by CFF to obtain more homogenous nanocellulose.

CFF and adsorption chromatography can be used to isolate dissolved wood components, yielding several upgraded products: lignin, lignin-carbohydrate complexes, and galactoglucomannan.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. 59 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014.9
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-143954 (URN)
Public defence
2014-04-25, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20140404

Available from: 2014-04-04 Created: 2014-04-03 Last updated: 2014-04-04Bibliographically approved

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Lindström, Mikael F.

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