Effect of Al2O3 on microstructure and dielectric properties of epoxy-cyanate ester composite material

The bisphenol A epoxy resin (E51) and biscyanatophenylpropane (BCE) were used as polymer matrix, Al2O3 (self-made with sol–gel method) as modified agent to prepare Al2O3/E51-BCE composites, and the thermal stability and dielectric properties of the composites were studied. FT-IR and transmission electron microscope (TEM) of Al2O3 showed that Al2O3 was short fiber-shaped crystal with hydroxyl groups on its surface. Scanning electron microscope (SEM) and energy-dispersive spectrum (EDS) analysis of Al2O3/E51-BCE composites indicated a strong interaction between Al2O3 and E51-BCE matrix resin, and the surface of the two phases was fuzzy. Al2O3 dispersed uniformly in the E51-BCE matrix as the dispersed phase. The interface among phases was blurred and showed a mutual penetrating phenomenon. Furthermore, the cross section of cracks was rough and the directions changed. This is a typical ductile fracture morphology. The highest value of the breakdown strength and volume resistivity of the Al2O3/E51-BCE composites were 15.1 kV/mm and 1.53 × 1015 Ω m, which was 13.5% and 86 times higher than that of the E51-BCE matrix, respectively, when the content of Al2O3 was 3 wt%. And the dielectric constant and dielectric loss tangent of the composite materials were 3.73 and 0.0029 at the electric field frequency of 100 Hz. Thermogravimetric curves displayed that the introduction of Al2O3 slightly decreased the thermal decomposition temperature during the range of 0 ~ 5 wt% Al2O3, but the thermal decomposition temperature of Al2O3/E51-BCE composites was all over 400 °C; the composite materials still had high heat resistance. Overall, this study facilitates the applications of Al2O3/E51-BCE composites in a broad range of fields.