Effect of Surface-Modified Nanosilicas on the Electrical Breakdown Strength in Epoxy Nanocomposites

Hydrophilic surface of fumed nanosilica was treated with a trimethylsilane coupling agent to achieve its hydrophobic surface, and the surface modification was confirmed by thermogravimetric weight loss and increasing contact angle of water droplet. The effects of the surface-modified nanosilica content on the electrical and mechanical properties of epoxy nanocomposites were studied to apply to the insulators for heavy electrical equipment. Epoxy nanocomposites were prepared by mixing epoxy base resin/curing agent/accelerator/trimethylsilane-modified nanosilica in the weight ratio of 100:80:1:0–7 g. High-voltage direct current breakdown strength increased with increasing modified nanosilica content. High-voltage alternating current breakdown strength was maximum when the nanosilica content was 1 phr (part per one hundred of epoxy resin), and thereafter, the value gradually decreased as the nanosilica content increased. Tensile strength of epoxy nanocomposite with trimethylsilane-modified nanosilica (7 phr) is 78.76 MPa, which is 20% higher than that of neat epoxy resin. The dielectric permittivity increases with increasing amount of the trimethylsilane-modified nanosilica.