Effective three-dimensional thermal conductivity networks in polystyrene/multi-walled carbon nanotubes/aluminum oxide@hexagonal boron nitride composites based on synergistic effects and isolated structures

Enhancing the thermal conductivity (λ) of composites by establishing an effective thermally conductive path is the key to prepare thermally conductive composites. In this study, a new preparation method was used to achieve high λ of composites with low filler contents. Firstly, multi-walled carbon nanotubes (MWCNT) and alumina (Al2O3) established a synergistic thermal conductivity network in the polystyrene particles, and subsequently, the hexagonal boron nitride (h-BN) filler wrapped in the outer layer of the composite particles constructed a continuous h-BN thermal conductivity network during the hot-pressing process. The three-dimensional thermal conductivity network supported by the two thermal conductivity networks provided more pathways for heat transfer in the composite, thus significantly improving its λ. The λ of the composites increased to 3.36 W/mK for MWCNT content of 0.5 wt%, Al2O3 content of 0.5 wt%, and h-BN content of 30 wt%. The composite also has good insulating properties, with a conductivity value of only 3.21 × 10−9 S/cm at an h-BN content of 30 wt% and MWCNT content of 0.5 wt%. This results from the presence of a h-BN insulation layer on the outside of the composite sphere and the presence of Al2O3 in the synergistic network that blocks the electron transport inside the material, thus maintaining its good insulating properties. Therefore, the composite prepared in this paper has the potential to be used in the field of electronic packaging.