Effect of heat treatment temperature on the microstructure and properties of polyimide-based carbon fibers

Polyimide(PI)-based carbon fibers with different properties were prepared by carbonization of PI fibers at 800 degrees C, followed by heat treatment from 800 to 2 800 degrees C. The effect of heat treatment temperature (HTT) on elemental composition, surface morphology, mechanical properties, and the thermal and electrical conductivities of PI-based carbon fibers were investigated by elemental analysis, SEM, HRTEM, Raman spectroscopy, mechanical testing, and electrical and thermal conductivity measurements. Results showed that as a result of HTT the carbon content increased from 78.97% to 99.72%, the tensile strength exhibited a maximum of 924.4 MPa, and the degree of graphitization and the size of graphite crystallites were both increased. Distinct reductions in strain-to-failure and electrical resistivity were observed with increasing HIT. The thermal conductivity can reach 228.4 W.m(-1).K-1 after heat treatment at 2 800 degrees C. PI fiber may be a good precursor for carbon fibers with a high thermal conductivity.