Performance of novolac resin- and resole resin-based carbon/carbon composites in relation to their fabrication conditions

The demands of cost-driven industrial applications can be satisfied by manufacturing composites with a low volume fraction of carbon fibres as phenolic carbon fibre-reinforced composites and C/C composites, both with acceptable performances, for low- or high-temperature applications, respectively. Polymeric composites reinforced with a low volume fraction (7.5% v/v) of carbon fibres were fabricated using laboratory-produced phenolic resins, novolac (N) and resole (R), as matrices after different curing/post-curing temperature profiles. By optimising the manufacturing conditions, the N-based polymeric composites exhibited higher flexural strength, whereas the R-based composites showed higher shear strength. C/C composites, namely N-based and R-based, were manufactured by pyrolysis of the previously prepared polymeric composites up to 1000 °C. The pyrolysed composites were then densified by impregnation with an appropriate resin solution, followed by curing and new pyrolysis, and particularly by employing 1 up to 4 consecutive cycles of ‘impregnation–curing/pyrolysis’. Weight changes resulting from the impregnation–curing and pyrolysis stages were determined. The curing of both resins was verified by Fourier Transform Infrared Analysis. The apparent density and X-ray diffraction data of the C/C composites were used to calculate their total percent porosities. The morphology and elemental composition of the C/C composites at their failure region (after flexural testing) were examined by Scanning Electron Microscopy/Energy-Dispersive X-ray Analyses. In comparison to the N-based C/C composites, the R-based ones exhibited: higher shear strength, lower flexural strength, higher Shore D hardness, slightly higher surface conductivity and lower volume conductivity. The optimum conditions for the manufacture of C/C composites were achieved by applying two consecutive cycles of ‘pyrolysis–impregnation–pyrolysis’ to the polymeric composites. © 2024 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.