Low pressure and humidity influences on the electret surface potential decay

Abstract

In the present paper the influence of both relative humidity and low pressure on the surface potential decay of charged 20 μm polypropylene films was investigated. Sample charging was performed in a three-electrode corona discharge system. After charging the initial surface potential was measured using the method of the vibrating electrode with compensation. Two groups of tests were performed. In the first group, after charging the electrets were placed into a vacuum chamber under various low pressures (from 0.1 mbar to 1000 mbar) for 30 minutes. After that the electrets were removed from the vacuum chamber. The surface potential was measured again and the normalized surface potential was calculated. The influence of low pressure was analyzed by the equation that describes processes of desorption from the electret surface. In the second group after charging the electrets were put in desiccators at 0% and 100% relative humidity for 220 days at room temperature. After that the surface potential was measured periodically out of the desiccators. The results obtained were analyzed with the percolation 2D model. It was established that the higher values of the relative humidity led to a faster decay of the surface potential. We assume the presence of surface discharge processes.