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

Abstract

AbstractThe 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.