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A new method for stabilizing softwood kraft lignin fibers for carbon fiber production
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
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2013 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 128, no 6, 3824-3830 p.Article in journal (Refereed) Published
Abstract [en]

Renewable resources, such as kraft lignin, have shown great potential as precursors for carbon fiber production. This manuscript reports an investigation into the stabilization of softwood kraft lignin (SKL) fibers and the determination of the difference in stabilization between hardwood- and softwood-based kraft lignin fibers. The stabilization was achieved either thermally by using only heat or oxidatively in the presence of air, at various heating rates. A heating rate of 4 degrees C min1 and a holding time of 30 min at 250 degrees C were successfully used for the thermal stabilization experiments. Faster stabilization was achieved using oxidative conditions at a heating rate of 15 degrees C min1 and 30 min holding time at 250 degrees C. Furthermore, stabilization and carbonization in a one-step process was performed on SKL fibers, which show great potential to reduce both production time and costs. The stabilized and carbonized fibers were evaluated using thermal, spectroscopic, and microscopic methods.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2013. Vol. 128, no 6, 3824-3830 p.
Keyword [en]
crosslinking, thermosets, biopolymers and renewable polymers
National Category
Polymer Technologies
URN: urn:nbn:se:kth:diva-92255DOI: 10.1002/app.38588ISI: 000316696000039OAI: diva2:513024

QC 20130429. Updated from manuscript to article in journal.

Available from: 2012-03-30 Created: 2012-03-30 Last updated: 2013-04-29Bibliographically approved
In thesis
1. Carbon Fibres from Kraft Lignin
Open this publication in new window or tab >>Carbon Fibres from Kraft Lignin
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Kolfiber från sulfatlignin
Abstract [en]

Kraft lignin has a high potential for use in more valuable applications than its current use as fuel in pulp mills and integrated pulp and paper mills. The possibility of using kraft lignin, a green material with a carbon content of more than 60 %, for the manufacturing of carbon fibres was investigated in this thesis. The strong and lightweight carbon fibre material has many potential application areas, e.g. in cars; the main obstacle limiting its demand is the high production cost, with the raw material (petroleum pitch and polyactrylonitrile) and fibre spinning constituting approximately 50 % of the cost.

Industrial kraft lignins originating from both softwood (spruce/pine) and hardwood (birch/aspen) were isolated with the LignoBoost technique and then purified and characterized to determine the best suitable lignin for the production of carbon fibre. Using ultrafiltration of the black liquor before isolation using the LignoBoost technique, a kraft lignin with satisfactory high purity was obtained. The fractionated kraft lignin can be used either as such or as a softening agent during melt spinning to obtain continuously spun kraft lignin fibres.

The behaviour during thermal treatment was found to differ depending on the type of kraft lignin used. After oxidative stabilisation, the studied lignins became more stable, and thus, the final yield after carbonisation was increased by 10-20 % in comparison to stabilisation in absence of oxygen. The identified products indicate that the main reactions during oxidative stabilisation are radical, oxidation, condensation and rearrangement reactions.

The structural differences between softwood and hardwood kraft lignins facilitated the stabilisation of the softwood lignin fibre as compared with the hardwood lignin fibres. Thermal stabilisation in an inert atmosphere using only heat was successfully achieved for the softwood kraft lignin fibres. Stabilisation and carbonisation was successfully performed in a one-step operation on softwood kraft lignin fibres. Thus, it seems possible that the separate stabilisation step can be omitted, which may reduce the processing costs of softwood kraft lignin-based carbon fibres.

Abstract [sv]

Sulfatlignin har hög potential för att kunna användas i mer värdefulla applikationer jämfört med idag då det främst används som bränsle i massabruk och integrerade massa/pappersbruk. I egenskap av ett grönt material med en kolhalt på mer än 60 %, har möjligheterna att använda kraftlignin vid kolfibertillverkning undersöks i den här avhandlingen. Kolfiber är lätt och starkt med många olika potentiella användningsområden. Det som idag huvudsakligen begränsar efterfrågan är den höga produktionskostnaden, där råmaterialet (petroleum pitch och polyakrylonitril) och fiberspinningen står för ca 50 % av kostnaden.

Industriella sulfatligniner från både barrved (gran/tall) och lövved (björk/asp) har framställts enligt LignoBoost-processen och har därefter renats och karaktäriserats med syfte att hitta det mest lämpliga råmaterialet för tillverkning av kolfiber. Genom att använda ultrafiltrering av svartlut innan isolering med LignoBoost-tekniken, kan man få ett kraftlignin som är tillräckligt rent. Det fraktionerade kraftligninet kan användas antingen rent eller som mjukgörare under smältspinning, för att få fram kontinuerligt spunna sulfatligninfibrer.

Sulfatligniner från olika vedslag beter sig olika under termisk behandling. Efter oxidativ stabilisering blir ligninerna mer stabila jämfört med stabilisering i frånvaro av syre, vilket medför ett högre utbyte med 10-20 % av den slutgiltiga kolfibern efter karbonisering. De viktigaste reaktionerna som sker under oxidativ stabilisering av fibrer från sulfatlignin är radikal-, oxiderings- och omlagringsreaktioner.

De strukturella skillnaderna mellan sulfatlignin från barrved och lövved gör det möjligt att stabilisera barrvedslignin mycket fortare. Termisk stabilisering i inert atmosfär med endast värme har lyckats med sulfatligninfibrer från barrved. Vidare har även stabilisering och karbonisering i ett enda steg lyckats med sulfatligninfibrer från barrved. Detta kan göra det möjligt att utesluta stabiliseringssteget, vilket förhoppningsvis kan reducera processkostnaderna för kolfiber från barrvedssulfatlignin.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xvii, 52 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2012:13
National Category
Engineering and Technology
urn:nbn:se:kth:diva-92256 (URN)978-91-7501-283-4 (ISBN)
Public defence
2012-04-20, STFI-salen, Drottning Kristinas väg 61, KTH, Stockholm, 10:00 (English)
QC 20120330Available from: 2012-03-30 Created: 2012-03-30 Last updated: 2012-03-30Bibliographically approved

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