Spectroscopic analysis of chemically modified carbon fibres

Abstract

Chemical treatments are used to introduce active functional groups and/or to increase the surface roughness of carbon fibres (CF) aiming to improve their interaction with polar polymeric matrices in composites. Considering the new challenges in the field of composite materials, such as the processing of hybrid composites and the growing use of thermoplastic structural composites, the modification of the CF surface has been increasingly studied. In this paper, the effect of various chemical treatments (with HCl, HNO3, H2SO4, CH3COOH, NH4OH, or H2O2) on the thermal stability, chemical composition, and microstructural parameters of a polyacrylonitrile‐based carbon fibre was investigated. Raman results indicated greater degree of crystallinity at the surface for the fibres treated (at 80°C for 1 h) with HCl, HNO3, H2SO4, and H2O2. The treatment with HCl at 80°C for 1 h was effective in reducing disturbance of the carbon structure, as indicated by the higher FWHMG value compared with those of the as‐received, acetone pretreated, and the other chemically treated carbon fibres. Fourier transform infrared (FTIR) showed that some treatments promoted an increase in CF polarity (H2SO4 at 80°C/1 h and NH4OH at 20°C/1 h), with the incorporation of organic polar groups (i.e., –OH). The apparent roughness of pretreated carbon fibre increased when treated with HNO3 at 80°C/1 h and H2SO4 at 80°C/1 h, as observed in the AFM analyses. AFM, FTIR, and Raman results suggest that the fibres treated with HNO3, H2SO4, and NH4OH were the most promising as reinforcement in high‐performance polymer composites.