Synergistic Enhancement of Through-Plane Thermal Conductivity in Graphite/PP Composites via Al/GO@AgNPs Hybrid Fillers

Graphite-filled polymer composites exhibit high in-plane thermal conductivity but suffer from severe thermal anisotropy, which limits their practical heat dissipation performance in the thickness direction. In this study, hierarchically structured Al/GO@AgNPs hybrid fillers were developed to enhance the through-plane thermal conductivity of polypropylene (PP)/graphite composites. The hybrid fillers were fabricated through GO-assisted surface modification of Al particles followed by electroless deposition of Ag nanoparticles. The GO layer improved the interfacial characteristics of Al and served as a platform for Ag nucleation, resulting in the formation of Ag nanoparticles on the Al/GO surface. When incorporated at a low loading of 1.0 wt%, the Al/GO@AgNPs hybrid filler increased the through-plane thermal conductivity from 11.24 to 48.33 W·m−1·K−1, corresponding to more than a fourfold enhancement compared with the graphite-only composite, while maintaining an in-plane thermal conductivity of 106.87 W·m−1·K−1. This improvement is attributed to the bridging effect of spherical hybrid fillers between adjacent graphite platelets and the resulting reduction in interfacial thermal resistance in the through-plane direction. The proposed hybrid filler system effectively mitigates thermal anisotropy and provides a promising strategy for designing highly filled polymer composites for advanced thermal management applications.