Measurement of Charging Tendency of Pellets by Impact Charging

The charging tendency of pellets of some synthetic high polymers are measured with a newly developed charging chamber in which the pellets are charged repeatedly by impacts against a metal plate by the use of a compressed air flow. The charge build-up of the pellets follows an almost exponential growth. It is shown that the saturation charge is limited by air breakdown. Furthermore, the time constant of the build-up curve shows how easily the sample acquires the charge. In the case of nearly spherical pellets of polyethylene, 0.16 cm in radius, the saturation charge density is -2.10 x 10-9 C/cm2. This value is 36.3% of the maximum theoretical value. The charging tendencies of nylon-6, polyethylene, and polystyrene shown by both the value of the time constant and the polarity, of the charge, agree with the triboelectric series.