Interfacial engineering for improving thermal conductivities of BNNS/PNF nanocomposite paper with superior electrical insulation and mechanical properties

With the rapid development of highly integrated and miniaturized electronic components, heat accumulation and signal attenuation in devices have become increasingly prominent. This underscores the urgent need to develop polymer-based composite paper with high thermal conductivity and low dielectric constant (ε). In this work, a PBO-analog compound (prePBO) is designed to functionalize boron nitride nanosheets (f-BNNS). Simultaneously, poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers are converted into PBO nanofibers (PNF) via deprotonation. Subsequently, the f-BNNS/PNF nanocomposite paper is fabricated via vacuum filtration followed by hot pressing. The prePBO enhances interactions between PNF and BNNS, reducing interfacial thermal resistance and suppressing interfacial phonon scattering. At 50 wt% f-BNNS loading, the f-BNNS/PNF nanocomposite paper achieves optimal thermal conductivities (λ_∥ = 10.37 W/(m K), λ_⊥ = 0.86 W/(m K)), representing 414 % and 480 % improvements over pristine PNF paper. Furthermore, due to the ultralow polarizability of fluorinated groups in prePBO and the nacre-mimetic structure, the nanocomposite paper presents low ε (3.15) and dielectric loss tangent (tanδ, 0.0221) at 1 MHz, alongside a volume resistivity of 3.3 × 10¹⁵ Ω cm and breakdown strength of 155.6 kV/mm. The nanocomposite paper also exhibits high tensile strength (114.55 MPa) and thermal decomposition temperature (640 °C), demonstrating promising potential for thermal management in high-power lithium batteries, ultrahigh-voltage capacitors, and related advanced applications.