Remarkable Thermal Conductivity of Epoxy Composites Filled with Boron Nitride and Cured under Pressure
Sasan Moradi, Frida Román, Yolanda Calventus, John M. Hutchinson
Abstract
This work demonstrates that the application of even moderate pressures during cure can result in a remarkable enhancement of the thermal conductivity of composites of epoxy and boron nitride (BN). Two systems have been used: epoxy-thiol and epoxy-diamine composites, filled with BN particles of different sizes and types: 2, 30 and 180 μm platelets and 120 μm agglomerates. Using measurements of density and thermal conductivity, samples cured under pressures of 175 kPa and 2 MPa are compared with the same compositions cured at ambient pressure. The thermal conductivity increases for all samples cured under pressure, but the mechanism responsible depends on the composite system: For epoxy-diamine composites, the increase results principally from a reduction in the void content; for the epoxy-thiol system with BN platelets, the increase results from an improved matrix-particle interface; for the epoxy-thiol system with BN agglomerates, which has a thermal conductivity greater than 10 W/mK at 44.7 vol.% filler content, the agglomerates are deformed to give a significantly increased area of contact. These results indicate that curing under pressure is an effective means of achieving high conductivity in epoxy-BN composites.