Electrical and mechanical properties of granular-fibrous carbon-carbon composites with recycled carbon fibres

In the following study, the electrical and mechanical properties of granular-fibrous carbon-carbon composites with short recycled carbon fibres have been investigated. The examined composites contained from 0 to 12 wt% of three types of recycled carbon fibres that differ in length. The conducted study has proven that it is not the type of applied fibre, but rather the resultant porosity of composites that exerts the predominant influence on the electrical resistivity and mechanical properties of the tested materials. The curve fitting revealed mathematical formulas correlating the studied properties with the apparent density of the composite samples. Owing to the addition of the shortest carbon fibres, the mechanical and electrical properties were significantly improved (50.14% and 24.06% increase in modulus of elasticity and flexural strength respectively for the sample with 12 wt% of the shortest fibres). A 21.39% decline in the resistivity (ϱ=161.26µΩ⋅m) of the composite containing 4% of shortest fibres was noted in comparison with the reference sample. Unlike powdered fibres, the addition of longer fibres caused an increase in porosity and deterioration of microstructure, which resulted in a significant decline in the key properties of the investigated composites.