A study of oxidation and water treeing in polyethylene

The authors report a study of a possible relationship between oxidation and water tree growth in laboratory-molded polyethylene under controlled conditions. To accelerate the oxidation which might occur during growth, a test series was performed at 75°C in addition to room temperature. After aging for preset times, specimens were removed and microtomed into 0.5-mm slices, and the insulation was checked for water trees with a microscope. The specimens were then dried for 20 h at 40°C under vacuum, and the oxidation level was measured by FTIR (Fourier transform infrared) spectroscopy coupled to an infrared microscope. Similar oxidation levels of treed and nontreed regions of insulation aged at room temperature indicate that oxidation is not required for the water tree growth. However, the tests at 75°C show that treed regions oxidize more rapidly at higher temperatures. This may be due to the contaminants in the trees acting as catalysts for oxidation