In this work, the influences of alumina (Al2O3) particle size and loading concentration on the properties of injection molded polycarbonate (PC)/boron nitride (BN)/Al2O3 composites were systematically studied. Results indicated that both in-plane and through-plane thermal conductivity of the ternary composites were significantly improved with the addition of spherical Al2O3 particles. In addition, the thermal conductivity of polymer composites increased significantly with increasing Al2O3 concentration and particle size, which were related to the following factors: (1) the presence of spherical Al2O3 particles altered the orientation state of flaky BN fillers that were in close proximity to Al2O3 particles (as confirmed by SEM observations and XRD analysis), which was believed crucial to improving the through-plane thermal conductivity of injection molded samples; (2) the presence of Al2O3 particles increased the filler packing density by bridging the uniformly distributed BN fillers within PC substrate, thereby leading to a significant enhancement of thermal conductivity. The in-plane and through-plane thermal conductivity of PC/50 μm-Al2O3 40 wt%/BN 20 wt% composites reached as high as 2.95 and 1.78 W/mK, which were 1183% and 710% higher than those of pure PC, respectively. The prepared polymer composites exhibited reasonable mechanical performance, and excellent electrical insulation properties and processability, which showed potential applications in advanced engineering fields that require both thermal conduction and electrical insulation properties.
Keywords: boron nitride; electrical insulation; injection molding; mechanical properties; microstructure; polycarbonate; spherical alumina; thermal conductivity.