Understanding the effect of lignin chemistry on the graphitic structure of lignin derived carbon fibres

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Carbon fibres have low density and high strength and stiffness and are hence used in lightweight materials, resulting in improved energy efficiency and fuel savings. However, the production of commercial carbon fibres is expensive and at present relies on the use of the petroleum-based precursors polyacrylonitrile (PAN) and mesophase pitch. Lignin is an abundant biopolymer and could be a low-cost renewable carbon fibre precursor. However, the strength and stiffness of lignin derived carbon fibres produced to date is variable and generally insufficient for most structural composite applications. In this project, we will understand how the chemical structure of lignin affects the arrangement of carbon atoms in the carbon fibres, the mechanisms by which the carbon arrangement forms and hence the arising material properties. This structure-property correlation requires an interdisciplinary approach that combines chemical analysis of lignin with materials production and analysis, with a view to chemical engineering practice, to design a cost-efficient production method. Precursor fibres will be stabilized, carbonized, and then graphitised to determine carbon yield, and explore the evolving microstructure. Material properties will be measured by tensile testing normalized to OM/SEM cross-sections. Importantly, the emerging graphitic structure of the carbon fibres will studied in detail using Raman spectroscopy and X-ray diffraction (with a focus on single/few fibre XRD) to correlate graphitic order with lignin chemistry. Given the variety of factors that can influence carbon fibre strength and stiffness, the large data set generated during this project will enable us to establish statistical correlations, separating the effect of polymer chemistry from processing effects.