The thermal and mechanical properties of carbon fiber/flake graphite/cyanate ester composites

Prepregs of carbon fiber reinforced cyanate ester (CE) resin matrix composites (CF/CE and CF/(10 wt% FG-CE)) were prepared with a laminate thickness of 2.0 mm and a fiber volume fraction of 60% with and without 10 wt% flake graphite (FG) as the CE filler. The rheological and thermal properties of the CE and FG/CE matrix as well as the thermal conductivity and mechanical properties of the CF/CE and CF/(10 wt% FG-CE) composites were investigated. Results indicated that the viscosity of the FG/CE matrix increased exponentially with increasing FG content and decreased significantly with deformation beyond 0.1% strain. A rheological percolation threshold was found at a FG content of 2-4 wt% and the percolation network of FG was broken at strains above 0.1%. The thermal conductivity of the matrix increased linearly with the FG content up to 0.46 W/(m·K) of 10wt%-FG/CE from 0.23 W/(m·K) of pure CE. The elastic modulus of the matrix increased from 2.9 GPa for pure CE to 4.3 GPa for 10 wt%-FG/CE. The thermal conductivity of the CF/(10 wt% FG-CE) composite was increased by 127% and compressive strength by 31% compared with the CF/CE composite.