Flexible towpreg for the fabrication of high thermal conductivity carbon/carbon composites

A continuous powder coating process was used to produce flexible, preimpregnated towpreg from a heat-treated Mitsubishi AR mesophase pitch powder (AR-120) and three different carbon fibers: T300 PAN-based fiber, P55 pitch-based fiber, and an experimental high thermal conductivity pitch-based ribbon fiber. The towpreg was hot-pressed into unidirectional composites, carbonized at 1100 °C, oxidized and then graphitized at 2400 °C. As expected, the PAN-based fibers developed strong fiber/matrix bonding and the pitch-based fibers developed poor fiber/matrix bonding. This resulted in high flexural strengths (841 MPa) in the graphitized composites reinforced with the T300 fibers and low flexural strengths (196 MPa) in the graphitized composites reinforced with the P55 fibers. In addition, it was found that during consolidation the ribbon fibers oriented normal to the pressing direction. The thermal conductivity (parallel to the fibers) of the graphitized T300/AR-120 and P55/AR-120 composites was 80.5 and 135.5 W/m · K, respectively. These results, along with X-ray analysis, indicated a significant development of preferred crystalline order (parallel to the fibers) upon graphitization at 2400 °C. The composites reinforced with ribbon fibers exhibited three-dimensional anisotropy, with a thermal conductivity (transverse to the fibers) of 213.5 W/m · K, higher than that parallel to the fibers (145 W/m · K). These results indicated that fiber shape can affect matrix properties in carbon/carbon composites. Finally, the towpreg was woven into a two-dimensional fabric, demonstrating that towpreg can be used to produce preimpregnated multidimensional composite preforms. Towpreg may provide a low-cost route for producing carbon/carbon composites.