Carbonization of cellulose fibre precursors: experimental and modelling efforts

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. Additional attractive feature is its renewability and bio-based origin. We have studied use of cellulosic fibres for production of carbon fibres. Our premise was that nitrogen content of cellulose carbamate fibres may be beneficial for the carbonization result. In experimental part we used wet-spun non-viscose fibres from enzymatically treated dissolved cellulose, so called BioCellSol cellulose and nitrogen containing cellulose carbamate. We studied use of various chemical agents, (NH4)2HPO4, H2SO4, and NH4Cl, in order to increase low carbon yield, and produced carbon and activated carbon materials. In order to obtain better understanding of carbonization of cellulose we performed reactive molecular dynamics simulations. In this presentation we review work carried out and results obtained within this study. In experimental study we learned for example, that carbon yield obtained with different impregnation agents (14 -21 %) was significantly higher than of non-treated reference (10%), best results obtained with (NH4)2HPO4. Strength of the obtained fibres was not as good as needed for load-bearing composite applications since we were not able to apply sufficient tensioning. However, coherent activated carbon fibres and nonwovens were obtained and they could be used e.g. for water purification and removal of odours from gas flow. Modelling efforts indicated that carbamation of cellulose is beneficial for both carbon yield in terms of carbon amount, and carbon quality in terms of amount carbon rings formed. 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 Innovation, VTT Technical Research Centre of Finland and Tampere University of Technology. Project was aiming for review possibilities to create bio-based carbon business in Finland.