Abstract: In this work, the mechanical properties and thermal conductivity of polyimide/graphite/ carbon fiber (CF) ternary composites were investigated. The synergistic effects between graphite and CF was studied with pseudo-binary system model. With increasing CF content, the tensile strength of PI/graphite/CF composite increased first and subsequently decreased. When the content CF was 11.8vol%, the tensile strength reached 66.37 MPa. The flexural strength of composite increased with increasing CF content. When the CF content was 24.6vol%, the flexural strength was 103.3MPa. The thermal conductivity of composites increased nonlinearly, which indicated that graphite and CF had a synergistic effect. SEM indicated when the volume of CF was 34.1%, thermally conductive pathway was formed by the crossover of CF and graphite resulting in a thermal conductivity of 0.512 W/(m·K), which was two times of the calculated value.

Key words: polyimide, carbon fiber, graphite, thermal conductivity, mechanical property