Dimension effect on thermal conductivity of hexagonal boron nitride/titanium dioxide reinforced hybrid PEEK composites developed with a scalable compounding approach

Abstract For the removal of elevated thermal flux in high‐temperature applications, there is an urgent need for robust and lightweight thermally conductive thermoplastic materials with suitable mechanical integrity. In current work, multiscale hexagonal boron nitride (hBN) and titanium dioxide (TiO 2 ) fillers are integrated into polyetheretherketone (PEEK) polymer to create a synergistic effect regarding thermal conductivity. An optimized twin‐screw extrusion is utilized to disperse the fillers uniformly in the host polymer by changing the screw design in terms of kneading, mixing, and reverse elements, feeding zones of the fillers/polymer, and the feeding cycles. Various specimens were developed by systematically varying the relative filler amount of the thermally anisotropic hBN and the thermally isotropic TiO 2 , while the total filler content was fixed to 60 wt%. As a result, 50B‐10T composite exhibited an ultrahigh thermal conductivity of 8.195 W/(m.K), with a 3139% enhancement compared to unfilled PEEK. Moreover, as the PEEK‐mediated regions are occupied with nano‐sized TiO 2 , efficient channels for phonon transport are formed between hybrid fillers, and the through‐plane thermal conductivity reached 1.704 W/(m.K) in 50B‐10T sample. The potential application of prepared composites as a heat spreader is demonstrated by monitoring surface temperature distribution and numerical simulation. Meanwhile, we achieved a synchronous improvement in mechanical stiffness within hybrid composites; and failure mechanisms including crack bridging at TiO 2 ‐PEEK interface, and debonding at hBN‐PEEK interface are observed in hybrid composites. Lastly, the high thermal stability makes the PEEK/hBN/TiO 2 specimens suitable for heat dissipation in demanding applications in the energy and aerospace sectors. Highlights Bespoke screw design developed for scalable manufacturing of Polyetheretherketone (PEEK) matrix composites reinforced with Hexagonal Boron Nitride (hBN) and Titanium Dioxide (TiO 2 ) via twin‐screw melt compounding. Interconnected 3D filler networks were achieved due to the filler dimension effect, allowing us to reach an ultrahigh in‐plane thermal conductivity value of 8.2 W/(m.K) and through‐plane thermal conductivity value of 1.7 W/(m.K) for 50B‐10T specimen. Manufactured hybrid PEEK/hBN/TiO 2 composite specimens possess excellent mechanical stiffness.