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Improved yield of carbon fibres from cellulose and kraft lignin
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
Swerea IVF, Box 104, SE-43122 Molndal, Sweden..
Swerea IVF, Box 104, SE-43122 Molndal, Sweden..
RISE Innventia, Box 5604, SE-11486 Stockholm, Sweden..
Show others and affiliations
2018 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 72, no 12, p. 1007-1016Article in journal (Refereed) Published
Abstract [en]

To meet the demand for carbon-fibre-reinforced composites in lightweight applications, cost-efficient processing and new raw materials are sought for. Cellulose and kraft lignin are each interesting renewables for this purpose due to their high availability. The molecular order of cellulose is an excellent property, as is the high carbon content of lignin. By co-processing cellulose and lignin, the advantages of these macromolecules are synergistic for producing carbon fibre (CF) of commercial grade in high yields. CFs were prepared from precursor fibres (PFs) made from 70: 30 blends of softwood kraft lignin (SW-KL) and cellulose by dry-jet wet spinning with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIm][OAc]) as a solvent. In focus was the impact of the molecular mass of lignin and the type of cellulose source on the CF yield and properties, while membrane-filtrated kraft lignin and cellulose from dissolving kraft pulp and fully bleached paper-grade SW-KP (kraft pulp) served as sources. Under the investigated conditions, the yield increased from around 22% for CF from neat cellulose to about 40% in the presence of lignin, irrespective of the type of SW-KL. The yield increment was also higher relative to the theoretical one for CF made from blends (69%) compared to those made from neat celluloses (48-51%). No difference in the mechanical properties of the produced CF was observed.

Place, publisher, year, edition, pages
WALTER DE GRUYTER GMBH , 2018. Vol. 72, no 12, p. 1007-1016
Keywords [en]
1-ethyl-3-methylimidazolium acetate (EMIMAc), carbon fibre (CF), cellulose, dissolving pulp, dry-jet wet-spun, fractionation, kraft pulp, LignoBoost lignin, molecular mass, softwood kraft lignin
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-239978DOI: 10.1515/hf-2018-0028ISI: 000451440900001Scopus ID: 2-s2.0-85050958001OAI: oai:DiVA.org:kth-239978DiVA, id: diva2:1269678
Note

QC 20181211

Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2019-02-25Bibliographically approved
In thesis
1. Carbon fibres from lignin-cellulose precursors
Open this publication in new window or tab >>Carbon fibres from lignin-cellulose precursors
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

It is in the nature of the human species to find solutions of complex technical problems and always strive for improvements. The development of new materials is not an exception. One of the many man-made materials is carbon fibre (CF). Its excellent mechanical properties and low density have made it attractive as the reinforcing agent in lightweight composites. However, the high price of CF originating from expensive production is currently limiting CF from wider utilisation, e.g. in the automotive sector.

 

The dominating raw material used in CF production is petroleum-based polyacrylonitrile (PAN). The usage of fossil-based precursors and the high price of CF explain the strong driving force of finding cheaper and renewable alternatives. Lignin and cellulose are renewable macromolecules available in high quantities. The high carbon content of lignin is an excellent property, while its structural heterogeneity yields in CF with poor mechanical properties. In contrast, cellulose has a beneficial molecular orientation, while its low carbon content gives a low processing yield and thus elevates processing costs.

 

This work shows that several challenges associated with CF processing of each macromolecule can be mastered by co-processing. Dry-jet wet spun precursor fibres (PFs) made of blends of softwood kraft lignin and kraft pulps were converted into CF. The corresponding CFs demonstrated significant improvement in processing yield with negligible loss in mechanical properties relative to cellulose-derived CFs. Unfractionated softwood kraft lignin and paper grade kraft pulp performed as good as more expensive retentate lignins and dissolving grade kraft pulp, which is beneficial from an economic point of view.

 

The stabilisation stage is considered the most time-consuming step in CF manufacturing. Here it was shown that the PFs could be oxidatively stabilised in less than 2 h or instantly carbonised without any fibre fusion, suggesting a time-efficient processing route. It was demonstrated that PF impregnation with ammonium dihydrogen phosphate significantly improves the yield but at the expense of mechanical properties.

 

A reduction in fibre diameter was beneficial for the mechanical properties of the CFs made from unfractionated softwood kraft lignin and paper grade kraft pulp. Short oxidative stabilisation (<2 h) of thin PFs ultimately provided CFs with tensile modulus and strength of 76 GPa and 1070 MPa, respectively. Considering the high yield (39 wt%), short stabilisation time and promising mechanical properties, the concept of preparing CF from lignin:cellulose blends is a very promising route.

Abstract [sv]

Det ligger i människans natur att hitta lösningar på komplexa tekniska problem, samt att alltid sträva efter förbättringar. Utvecklingen av nya material är inget undantag. Ett av flera material utvecklade av människan är kolfiber. Dess utmärkta mekaniska egenskaper samt låga densitet har gjort det attraktivt som förstärkningsmaterial i lättviktskompositer. Det höga priset på kolfiber, vilket härstammar ur en kostsam framställningsprocess, har förhindrat en mer utbredd användning i exempelvis bilindustrin.

 

Det dominerande råmaterialet för kolfiberframställning är petroleumbaserad polyacrylonitril (PAN). Användandet av fossila råvaror och det höga priset på kolfiber förklarar den starka drivkraften att hitta billigare och förnyelsebara alternativ. Lignin och cellulosa är förnyelsebara makromolekyler som finns tillgängliga i stora kvantiteter. Det höga kolinnehållet i lignin gör det mycket attraktivt som råvara för kolfiberframställning, men dess heterogena struktur ger en kolfiber med otillräckliga mekaniska egenskaper. Däremot har cellulosa en molekylär orientering som är önskvärd vid framställning av kolfiber, men dess låga kolinehåll ger ett lågt processutbyte som i sin tur bidrar till höga produktionskostnader.          

 

Det här arbetet visar att många av de problem som uppstår med kolfiber från respektive råvara kan kringgås genom att utgå från blandningar av desamma. Prekursorfibrer från blandningar av kraftlignin och kraftmassa från barrved tillverkade med luftgapsspinning konverterades till kolfiber. Utbytet för kolfibrerna som framställdes var mycket högre än vid framställning från endast cellulosa. Ofraktionerat barrvedslignin och kraftmassa av papperskvalitet presterade lika bra som de dyrare retentatligninen och dissolvingmassan, vilket är fördelaktigt ur ett ekonomiskt perspektiv.

 

Stabilisering är det mest tidskrävande processteget i kolfibertillverkning. I det här arbetet visades det att prekursorfibrerna kunde stabiliseras på kortare än två timmar, eller direktkarboniseras utan någon sammansmältning av fibrerna. Detta indikerar att en tidseffektiv produktion kan vara möjligt. Impregnering av prekursorfibrerna med ammoniumdivätefosfat ökade utbytet avsevärt, men med lägre mekaniska egenskaper som bieffekt.        

 

Kolfibrernas mekaniska egenskaper ökade vid en diameterreduktion. En kort oxidativ stabilisering under två timmar i kombination med tunna prekursorfibrer gav kolfiber med en elasticitetsmodul på 76 GPa och dragstyrka på 1070 MPa. Att göra kolfiber från blandningar av lignin och cellulosa är ett lovande koncept om det höga utbytet (39%), den korta stabiliseringstiden samt de lovande mekaniska egenskaperna tas i beaktande. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 40
Series
TRITA-CBH-FOU ; 2019.11
Keywords
Carbon fibre, Kraft lignin, Cellulose, Dry-jet wet spinning, Kolfiber, Sulfatlignin, Cellulosa, Våtspinning, Luftgapsspinning
National Category
Materials Chemistry Paper, Pulp and Fiber Technology Composite Science and Engineering
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-244756 (URN)978-91-7873-107-7 (ISBN)
Presentation
2019-03-22, Innoversum, RISE Bioeconomy, Drottning Kristinas väg 61, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Note

QC 20190226

Available from: 2019-02-26 Created: 2019-02-25 Last updated: 2019-02-26Bibliographically approved

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