Highly anisotropic thermally conductive polyimide composites via the alignment of boron nitride platelets

In this work, highly anisotropic thermally conductive polyimide/boron nitride (PI/BN) composites were successfully prepared by a simple method called ball milling, high-pressure compression and low-temperature sintering. The in-plane thermal conductivity of the PI composites with 30wt% BN reached as high as 2.81 W/mK, while the out-of-plane thermal conductivity was 0.73 W/mK, about 3.2 times and 2.4 times of pure PI, respectively. The great improvement of the thermal conductivity was attributed to the in-plane alignment of BN platelets, which constructed highly connected thermally conductive pathways. The thermally conductive BN networks were observed to be more dense and sufficient in the in-plane direction, more favorable for the heat dissipation, compared to the out-of-plane direction.