Investigating the mechanism of inducing colours onto carbon fibres via electrochemical oxidation

Anodic electrochemical oxidation was utilised to modify the nanostructure surface of carbon fibre (CF) to produce colour. The focus of this study was investigating the underlying mechanism responsible for generating colour in H2SO4, MgSO4, H3PO4, HNO3, TBA HSO4 and SDS treated CF. Test conditions were examined including electrolyte concentration, applied potential, treatment time, temperature and amperage. The combination of these factors with molecular anion from each electrolyte influenced colour displayed on CF and colors were able to be modulated. Helium ion microscopy images of MgSO4, H3PO4 and HNO3 revealed possible film and or etching of nanostructure surface. Theoretical mechanism of H2SO4 installing oxygenated groups on CF surface and relationship to colour production was explored. SDS images had a complete film generated on surface and speculative process of self-assembly on CF resulting in colour was discussed. Atomic force microscopy of treated fibres had insignificant lower roughness average compared to pristine control sample. MgSO4, H3PO4 and H2SO4 had water contact angles above 90� indicating high surface tension and low wettability. Favimat testing revealed that HNO3 was the only treated CF that met industry grade for standard CF in tensile modulus and strength. Whereas degradation in tensile strength was observed in other electrolytes.