Highly Anisotropic, Thermally Conductive, and Mechanically Strong Polymer Composites with Nacre-like Structure for Thermal Management Applications

The conventional approach to improve the thermal conductivity (TC) of polymers by blindly adding inorganic fillers suffers from the limited TC enhancement (<3.0 W/mK) with isotropic TC and poor mechanical performance. Here, highly anisotropic, thermally conductive, and mechanically strong boron nitride (BN)/ultrahigh molecular weight polyethylene composites are prepared via a facile solid-phase extrusion (SPE) technology. The in-plane TC approaches 12.42 W/mK at the BN loading of 50 vol %, which is 242% higher than that of the high-pressure compressed counterpart (3.63 W/mK). The anisotropic index of TC reaches as high as ∼1000%, allowing the heat transfer more readily along in-plane direction than through-plane direction as revealed by infrared imaging results. We attribute the increased TC to the unique nacre-like structure induced by the flow-assisted alignment. BN platelets are highly oriented to form connected thermal conductive pathways for phonon transport along the basal plane. The interfacial thermal resistance is reduced by 2 orders of magnitude as deduced by theoretical calculation. More strikingly, compared to the controlled samples with randomly distributed structure, SPE composites exhibit significantly superior strength and toughness at equivalent filler content. These results demonstrate that the prepared SPE composites have high potential for the engineering application in heat dissipation fields.