Impacts of thermal aging and water absorption on the surface electrical and chemical properties of cycloaliphatic epoxy resin

New techniques for measuring surface degradation are applied to the study o f surface tracking resistance of materials intended for outdoor use. cycloa liphatic epoxy resin (CAE) with 200 pph silica powder was aged under accele rated conditions for 100 h (100 to 250 degrees C) and then its tracking res istance was assessed. The tracking resistance of CAE that was exposed to wa ter absorption (0 to 3.3%) also is evaluated. Changes on the surface layer (1 to 10 mu m) with thermal treatment are revealed by employing scanning el ectron microscopy (SEM)-energy dispersive X-ray (EDX) analysis, attenuated total reflection (ATR)-Fourier transform infrared (FTIR), reflective visibl e spectroscopy and thermal gravimetry (TG)-differential thermal analysis (D TA)-mass spectrometry (Ms). The tracking resistance of CAE aged above 170 d egrees C is particularly reduced. Surface resistivity declines with rising temperature of thermal aging. The lowering of surface resistivity enlarges the leakage current passing at the aged surface layer and increases the sur face temperature of CAE. This would accelerate thermal aging. It also is sh own that absorbed water in CAE decreases tracking resistance. The effect of absorbed water during the initial stage of a tracking test is described. U nder saline pollution and moisture, thermal aging affects not only surface tracking but also electrochemical erosion derived from sodium hydroxide whi ch forms through electrolysis of sodium chloride. Electrochemical erosion e nhances water uptake for CAE, which can lead to tracking resulting from abs orbed water.