Improvement in surface degradation properties of polymer composites due to pre-processed nanometric alumina fillers

Insulating materials in power apparatus are often exposed to surface discharges in the course of normal operation, resulting in deterioration of the material surface. In an earlier work, the authors have shown that the inclusion of nanometric particles (Al2O3) improves the ability of a polymeric dielectric (epoxy) to resist degradation when exposed to surface discharges. In the current work, the effect of pre-processing the alumina nanoparticles before preparation of the composite, is investigated. Laser Surface Profilometry (LSP) was used to measure the degradation of the composite specimens after exposure to surface discharges. The use of a surfactant, viz. Sodium Dodecyl Sulfate (SDS) was found to be ineffective. However, the simple action of heating the nanoparticles before use, improved the resistance of the bulk composite to surface discharges. Further, the particles were functionalized using 3-glycidoxy-propyltrimethoxysilane (GPS). This process greatly enhanced the ability of the nanocomposite to resist surface degradation. In fact, best results were obtained when the particles were first heated and then coated with GPS. Fourier Transform Infra-Red (FTIR) spectroscopy and other techniques were used to investigate chemical changes at the particle-epoxy interfaces. A direct correlation was observed between the improvement of the resistance of the composite to surface degradation and the ability of the pre-processed nanoparticles to form strong bonds with the neighboring epoxy. Effect of pre-processing particles of larger dimensions (platelets) was negligible compared to nanoparticles, indicating the possible importance of the interfacial surface to volume ratio of the fillers.