Effect of h‐ BN and Aluminosilicate Filler Configuration and Distribution on Thermal Conductivity and Structural Integrity of Hybrid PEEK Composites

ABSTRACT Achieving high through‐plane thermal conductivity (TC) and mechanical strength in PEEK‐based composites at high filler loadings is limited by processing challenges, poor filler‐matrix interfaces, and filler aggregation. This work addresses these issues by using a hybrid filler approach using hexagonal boron nitride (hBN) and aluminosilicate (AlS) fillers in a PEEK matrix via an optimized twin‐screw co‐extrusion. During processing, controlled melt flow facilitated the polymer‐assisted filler separation, preserving hBN's platelet form and enabling a synergistic hybrid effect at a combined 60 wt% loading. Results show that composites with higher hBN content exhibited greatly enhanced TC, with the 50 wt% hBN/10 wt% AlS formulation achieving 7.992 W/(m K) in‐plane and 1.785 W/(m K) through‐plane, 3059% and 738% improvements over neat PEEK. Those with higher AlS content demonstrated improved mechanical properties, with 10 wt% hBN/50 wt% AlS composite reaching tensile strength of 96.31 MPa, matching neat PEEK and outperforming single filler hBN/PEEK by 44%. Rheological studies revealed shear‐thinning behavior of hybrid composites, with melt viscosity tunable by adjusting filler ratios. The composites also maintained excellent thermal stability under typical operating temperatures (≤ 250°C). Thus, current work presents a scalable co‐extrusion process for developing robust, thermally conductive hybrid PEEK composites by addressing the critical challenge of co‐optimizing thermal conductivity and mechanical strength, positioning these materials as strong candidates for high‐performance thermal management applications.