Carbon fibres from regenerated cellulose fibre precursors

Cellulose was first precursor fibre material used for production of carbon fibres. It has been in many application replaced with polyacrylonitrile (PAN) and isotropic pitch, especially in high modulus applications. However, cellulose and more precisely viscose (rayon), has still remained some markets due to beneficial properties including good thermal stability of resulted fibres, and low price of raw material and precursor fibre production compared to PAN. Additional attractive feature is its renewability and bio-based origin. We have studied the use of regenerated cellulosic fibres for production of carbon fibres. We used wet-spun non-viscose fibres from enzymatically treated dissolved cellulose, so called Biocelsol fibres, and nitrogen containing cellulose carbamate. We studied the use of various chemical agents, (NH4)2HPO4, H2SO4, and NH4Cl, in order to increase low carbon yield and produced carbon fibres and activated carbon fibres and nonwovens. In this presentation we review work carried out and results obtained within this study. In preliminary trials we studied the effect of different impregnation agents on carbon yield. Obtained carbon yields in these un-optimized cases were 14 -21 %, which was significantly higher than of non-treated reference (10%). Best carbon yield was obtained with (NH4)2HPO4, which was selected for sample preparation. We produced both carbon fibres with tensioning during carbonization as well as CO2 activated carbon fibres. Strength of the obtained carbon fibre samples was not as good as needed for load-bearing composite applications, since we were not able to apply sufficient tensioning. With better optimized carbonization process we, however, were able to obtain carbon yield of above 30 % and fibres showed good conductivity (above 4000 S/m). Possible use of such material could be e.g. conductive filler in non-load-bearing applications. Activated carbon fibres and nonwovens had surface areas above 1000 m2/g and single samples even above 2000 m2/g. Fibre and nonwovens were coherent and they could be used e.g. for water purification and removal of odours from gas flow. This work was carried out in 'Bio-Based Tailored Precursors for Advanced Carbons and Applications' (BioPreCarb) project funded by Tekes - the Finnish Funding Agency for Technology and Innovation, VTT Technical Research Centre of Finland and Tampere University of Technology. Project was aiming to review possibilities to create bio-based carbon business in Finland.