Critical agglomerate sizes to improve the insulation characteristics of epoxy/TiO2 nanocomposites

Agglomerates of nanoparticles which inevitably occur in the fabrication process of epoxy nanocomposite can affect the insulation properties of epoxy nanocomposite. This paper presents an attempt to clarify the effect of agglomerate size on two important insulation properties of epoxy/TiO2 nanocomposite (NC). One is intrinsic AC breakdown strength and the other is long-term partial discharge lifetime. We used a centrifugation technique to control the maximum size of the agglomerates in the range from 5 μm down to 0.05 μm in each sample. As the results, AC intrinsic breakdown strength was increased with decreasing the maximum agglomerate size and became even higher than the neat epoxy resin when the maximum size is less than around 0.05um. On the other hand, partial discharge lifetime decreased with decreasing the maximum agglomerate size. It should be noted that the PD lifetime distinctively decreased when the agglomerate size is less than around 0.2 um indicating the existence of a critical agglomerate size which contribute to the suppression of partial discharge development resulting in the extension of the partial discharge lifetime.