Anisotropic mPPO/TiO₂ composites with enhanced permittivity and thermal conductivity via planar and uniaxial orientation strategies

Ceramic-filled polymer matrix composites (PMCs) combine the excellent dielectric properties of ceramics with the toughness and processability of polymers. Among the various types of PMCs, 0–3 type composites have been widely studied. However, their dielectric constant (εᵣ) and thermal conductivity (κ) remain relatively low. Inspired by orientation engineering, performance enhancement in specific directions can be achieved by ordering fillers with geometric or crystalline anisotropy. Since the crystal c-axis of rutile aligns with the long axis of the filler, both mechanisms synergistically enhance performance. We devised two strategies, planar and uniaxial, to control the alignment of moderate-aspect-ratio TiO₂ in a modified polyphenylene oxide (mPPO) matrix. Planar orientation is achieved through hot pressing, whereas uniaxial orientation is induced hydrodynamically via shear and extensional flow. The uniaxial orientation strategy achieves a more pronounced anisotropy, with a significant enhancement of the ε_r and κ in the orientation direction, reaching a dielectric constant of ∼16, a thermal conductivity of ∼1 W m⁻¹ K⁻¹, and a coefficient of thermal expansion of only 30 ppm/K for composite filled with 50 vol% TiO₂. Importantly, the strategy proposed in this paper is fully compatible with the industrial screw extrusion process, making it suitable for large-scale production.