Thermal properties of carbon fibre/epoxy composites modified by novolac resin

The influence of novolac resin (NR) contents of 7–18 wt-% on the thermal degradation of the carbon fibre/epoxy composites was investigated by thermogravimetric analysis. The initial decomposition temperature, decomposition temperature at 10 wt-% weight loss T10%, temperature of maximum rate of weight loss Tmax and the decomposition activation energy E based on the Horowitz–Metzger calculation method were characterised in a thermal stability study. The results showed that both the curing reaction and the properties of the composites were affected by NR. Different trends were observed for <13 wt-% and >13 wt-%NR content. For <13 wt-%NR content, single NR particles seemed to play an important role. For 18 wt-%NR content, the behaviour can be explained as mainly an agglomeration effect. Thermal stability properties were sacrificed to some extent with the improvement of toughness. However, 7–13 wt-%NR content in the composites resulted in a better thermal stability than 18 wt-%NR. This is probably due to the effect of the inherent NR properties in the NR transition layer between fibre and matrix. The improvement of toughness was also proved by the impact properties of composites.