In-Plane Thermal Conductivity in Thin Carbon Fiber Composites

The objective of this study was to determine whether fiber type, fiber angle, and filler material affected the in-plane thermal conductivity of thin (7-15 mils thickness) carbon fiber composites. Two sets of samples were tested: low thermal conductivity samples made with polyacrylonitrile-based fibers (k = 6.8 W/m .K) in Fiberglast epoxy resin, and high thermal conductivity samples fabricated with coal-pitch-based fibers (k = 620 W/m . K) in cyanate ester resin. Samples were fabricated from 0/90 woven cloths and warped to obtain a range of fiber-pattern angles from 25/ - 25 to 65/ - 65. The filler effect on thermal conductivity was evaluated on additional samples prepared with 10% volume fraction of graphite powder in the matrix. Thermal conductivity of the low thermal conductivity samples was in the range of 15-20 W/m . K and showed up to a 15 % improvement when the angle of the fibers was varied. High thermal conductivity samples showed thermal conductivities between 60 and 150 W/m . K, with an improvement up to 60% when the angle of the fibers relative to the heat flux direction was changed from 0/90 to 25/-25. The samples with graphite powder did not show any enhancement in thermal performance. As potential alternatives, unidirectional tape and eGraf's Spreadershield® foils were also tested, showing good thermal performance.