Highly Filled Graphite/Polyetheretherketone Composite Filaments for Fused Deposition Modeling: Interfacial Compatibility, Rheological Properties, and Microwave Absorption Performance

Graphite (GP) suffers from chemically inert surfaces and weak interfacial bonding with polyetheretherketone (PEEK), while high filler loadings cause severe agglomeration and deteriorate composite processability and mechanical properties. Herein, GP/PEEK composites with 15-25 wt% GP were prepared via melt blending, by compounding PEEK matrices with different melt flow indices and screening processing aids. The results show that blending PEEK 330 and PEEK 8002 at a 1:1 mass ratio significantly improves GP dispersion and interfacial compatibility, with no obvious agglomeration even at 25 wt% loading. The 25 wt% GP composite exhibits 15 °C higher initial decomposition temperature than neat PEEK, elasticity-dominated melt behavior and good shear thinning properties. It retains tensile and flexural strengths of 63.45 MPa and 74.07 MPa, respectively, with enhanced storage modulus and glass transition temperature. For microwave absorption, it achieves a minimum reflection loss of -18 dB at 7.7 GHz (4.4 mm thickness) with an effective bandwidth of 2 GHz. This work provides technical references for interface regulation and processing optimization of highly filled GP/PEEK composites for structural-functional integrated applications.