Abstract:

Hetero-structured thermally conductive spherical boron nitride and boron nitride nanosheets (BNN-30@BNNS) fillers were prepared via electrostatic self-assembly method. And the corresponding thermally conductive & electrically insulating BNN-30@BNNS/Si-GFs/E-44 laminated composites were then fabricated via hot compression. BNN-30@BNNS-III (fBNN-30/fBNNS, 1/2, wt/wt) fillers presented the optimal synergistic improvement effects on the thermal conductivities of epoxy composites. When the mass fraction of BNN-30@BNNS-III was 15 wt%, λ value of the BNN-30@BNNS-III/E-44 composites was up to 0.61 W m^-1K^-1, increased by 2.8 times compared with pure E-44 (λ = 0.22 W m^-1K^-1), also higher than that of the 15 wt% BNN-30/E-44 (0.56 W m^-1K^-1), 15 wt% BNNS/E-44 (0.42 W m^-1K^-1), and 15 wt% (BNN-30/BNNS)/E-44 (direct blending BNN-30/BNNS hybrid fillers, 1/2, wt/wt, 0.49 W m^-1K^-1) composites. The λ in-plane (λ_//) and λ cross-plane (λ_┴) of 15 wt% BNN-30@BNNS-III/Si-GFs/E-44 laminated composites significantly reached 2.75 W m ^-1K^-1 and 1.32 W m^-1K^-1, 186.5 % and 187.0 % higher than those of Si-GFs/E-44 laminated composites (λ_// = 0.96 W m^-1K^-1 and λ_┴ = 0.46 W m^-1K^-1). Established models can well simulate heat transfer efficiency in the BNN-30@BNNS-III/Si-GFs/E-44 laminated composites. Under the condition of point heat source, the introduction of BNN-30@BNNS-III fillers were conducive to accelerating heat flow transfer. BNN-30@BNNS-III/Si-GFs/E-44 laminated composites also demonstrated outstanding electrical insulating properties (cross-plane withstanding voltage, breakdown strength, surface & volume resistivity of 51.3 kV, 23.8 kV mm^-1, 3.7 × 10¹⁴ Ω & 3.4 × 10¹⁴ Ω·cm, favorable mechanical properties (flexural strength of 401.0 MPa and ILSS of 22.3 MPa), excellent dielectric properties (ε of 4.92 and tanδ of 0.008) and terrific thermal properties (T_g of 167.3 °C and T_HRI of 199.2 °C).

Key words: Epoxy resins, Thermally conductive laminated composites, Glass fabrics, Hetero-structured fillers