Thermally Conductive and Insulating Epoxy Composites by Synchronously Incorporating Si-sol Functionalized Glass Fibers and Boron Nitride Fillers

Glass fibers (GFs)/epoxy laminated composites always present weak interlaminar shear strength (ILSS) and low cross-plane thermal conductivity coefficient (λ_⊥). In this work, silica-sol, synthesized from tetraethyl orthosilicate (TEOS) and KH-560 via sol-gel method, was employed to functionalize the surface of GFs (Si-GFs). Together with a spherical boron nitride (BNN-30), the thermally conductive BNN-30/Si-GFs/epoxy laminated composites were then fabricated. Results demonstrate that Si-sol is beneficial to the improvement of mechanical properties for epoxy laminated composites (especially for ILSS). The BNN-30/Si-GFs/epoxy laminated composites with 15 wt% BNN-30 fillers display the optimal comprehensive properties. In-plane λ(λ_//) and λ_⊥ reach the maximum of 2.37 and 1.07 W·m⁻¹·K⁻¹, 146.9% and 132.6% higher than those of Si-GFs/epoxy laminated composites (λ_// = 0.96 W·m⁻¹·K⁻¹ and λ_⊥ = 0.46 W·m⁻¹·K⁻¹), respectively, and also about 10.8 and 4.9 times those of pure epoxy resin (λ_// = λ_⊥ 0.22 W·m⁻¹·K⁻¹). And the heat-resistance index (T_HRI), dielectric constant (ε), dielectric loss (tanδ), breakdown strength (E₀), surface resistivity (ρ_s) as well as volume resistivity (ρ_v) are 197.3 °C, 4.95, 0.0046, 22.3 kV·mm⁻¹, 1.8 × 10¹⁴Ω, and 2.1 × 10¹⁴Ω·cm, respectively.