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.
Highlights
Epoxy composites filled with boron nitride (BN) are widely used for heat management in Insulated Metal Substrates (IMS)
The effects of BN filler size and type have been investigated previously [5,6], and it has been shown that, for a given filler content, the thermal conductivity generally increases with particle size; the usual interpretation is that larger particles have a smaller interfacial contact area with the matrix, this interface presenting a barrier to phonon transport
In most cases there is a correlation between the density and the thermal conductivity, but the mechanisms for enhancing the thermal conductivity depend on the particular epoxy-BN system
Summary
Epoxy composites filled with boron nitride (BN) are widely used for heat management in Insulated Metal Substrates (IMS). Such materials must satisfy a number of requirements, including adhesion, processability, electrical insulation, and high thermal conductivity. The last of these has attracted considerable attention, and the state of the art in polymerbased composites in general [1,2], and in epoxy-BN composites in particular [3], has been reviewed recently. It was found [6] that agglomerates result in a higher thermal conductivity than do platelets
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