Through-thickness thermal conduction in glass fiber polymer–matrix composites and its enhancement by composite modification

Continuous glass fiber polymer–matrix composites are electrically insulating and used for printed wiring boards, but their thermal conductivity needs to be increased without sacrificing the electrical insulation ability. The through-thickness thermal conductivity of these epoxy–matrix composite laminates with in-plane fibers is found to be effectively modeled using the Rule of Mixtures with fibers and matrix mainly in parallel in the through-thickness direction, in contrast to the series model that is effective for previously studied carbon fiber composites. For the glass fiber composites, the through-thickness conductivity is similar to the in-plane conductivity. The conductivity for woven fiber composites is increased by up to 80 % by curing pressure increase (from 0.69 to 4.0 MPa), up to 50 % by solvent (toluene or ethanol) treatment of the prepreg for partial surface resin removal, and up to 90 % by boron nitride nanotube (BNNT) incorporation along with solvent treatment. The highest through-thickness thermal conductivity reached is 1.2 W/(m K), which is higher than those of all prior reports on glass fiber composites. The interlaminar interfaces are negligible in through-thickness thermal resistance compared to the laminae, as for previously studied carbon fiber composites. The fiber contribution dominates the lamina resistance. The fiber–fiber interface contribution to the lamina resistance decreases significantly with curing pressure increase or composite modification involving BNNT incorporation or solvent treatment of the prepreg.