Distribution of Electric Potential at the Surface of Corona-Charged Polypropylene Nonwoven Fabrics After Neutralization

Accumulation of electric charges on insulating surfaces is frequently at the origin of severe electrostatic hazards. The best solution to this problem is to neutralize these charges by the use of ac corona discharges. The aim of this work is to evaluate the efficiency of this process in the specific case of fibrous electrets, by measuring the repartition of the electric potential at the surface of nonwoven polypropylene fabrics before and after neutralization. The samples were charged for 10 s,in ambient air, using a triode-type corona electrode system of positive polarity. In all the experiments, the neutralization was performed 180 s after the charging process. In some of them, the neutralization electrode (tungsten wire with a diameter of 0.3 mm) was fixed at a given distance (50 mm) above the samples and energized from an ac voltage amplifier (model 30/20A, Trek, Inc., Medina, NY, USA). In other experiments, the samples moved at constant speed (3 cm/s) in the ac corona discharge zone generated by the neutralization electrode. The experimental results show that the efficiency of neutralization (expressed as the relative reduction of the average potential measured at the surface of the sample) depends on the amplitude and the frequency of the sinusoidal high voltage, as well as on the charging time and the neutralization duration. Better effects were recorded in the case of the samples that moved through the corona discharge zone.