Analysis of surface degradation of epoxy nanocomposite due to tracking under AC and DC voltages R. Sarathi * , P. Rajesh Kumar, R.K. Sahu Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India Received 28 October 2006; received in revised form 22 December 2006; accepted 5 January 2007 Available online 14 January 2007 Abstract The tracking phenomenon, a carbonaceous process, in epoxy nanocomposite material has been studied under the AC and DC voltage in the present work. It was observed that the tracking is more severe under the DC voltages, especially under positive DC voltage when compared to negative DC voltage. The leakage current during the tracking studies was measured and moving average technique was used to characterize the trend of current flow. It was noticed that an increase in nanoclay content to epoxy resin shows a reduction in magnitude of leakage current flow during tracking test. It was also observed that the magnitude of leakage current is more under negative DC voltage compared with positive DC/ AC voltage. The magnitude of leakage current and the tracking time shows inverse relationship as evident from the present study. A drastic reduction in contact angle was observed for the specimens subjected to tracking test. It was confirmed that surface discharges also cause per- manent damage to the insulating material. The WAXD studies indicated that up to 5 wt% of nanoclay in epoxy resin resulted in exfoliated struc- ture. The TEM studies were carried out on the nanocomposite structures. The TGeDTA results showed that a maximum degradation of epoxy resin occurs at around 300  C. From the EPR study it is realized that, in the tracking formed zone the spin concentration is more in epoxy nano- composites indicating that tracking as a damage generating process. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Epoxy resin; Nanocomposites; Insulation; Degradation; Tracking; Leakage current 1. Introduction Nanocomposites are a class of hybrid materials where one of the constituents has dimensions in the range between 1 and 100 nm. Polymer nanocomposites are emerging as a new class of materials for its demanding applications as insulating mate- rial [1,2]. The epoxy resin is used not only as insulating mate- rial but also as structural material because it is cost-effective. Epoxy resin added with organically modified clay as filler finds major application in recent years [3e7]. The selection of clay as reinforcing material is extremely appealing because of cost, high thermal inertness, and eco-friendly characteris- tics. One of the major problems with the insulators is the tracking and erosion of polymer structures [8,9]. Tracking, which is a peculiar phenomenon, occurs on the surface of the insulation structure because of the creepage discharge re- sulting from surface contamination during operation. The im- pact of discharge varies with the surface field intensity, surface current magnitude and the state of discharge thereby induced, all of which are due to surface wetting and the degree of con- tamination. Once tracking occurs, the surface electrical insula- tion property is lost completely and it never recovers. In order to improve the reliability and the performance of the insulation materials, the tracking phenomenon is being investigated worldwide. Having known all this, in the present work, an experiment was designed according to IEC-60 587 [10], to investigate the tracking phenomena in epoxy nanocomposites material under AC and DC voltages, with ammonium chloride as the contam- inant. The impact of nanoclay content in epoxy resin on leak- age current flow over the surface of insulating material during * Corresponding author. Tel.: þ91 44 2257 4436; fax: þ91 44 2257 4402. E-mail address: rsarathi@iitm.ac.in (R. Sarathi). 0141-3910/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2007.01.014 Polymer Degradation and Stability 92 (2007) 560e568 www.elsevier.com/locate/polydegstab