Bipolar charging in polydisperse polymer powders in industrial processes

The purpose of this paper is to review the previous published work and to describe some results showing bipolar charging using polymer powders in two common industrial processes: fluidized beds and pneumatic transport. A new measurement system is described for measuring the bipolar charge distribution. This consists of a vertical array of seven Faraday pail sensors, which can selectively detect different charge components based upon particle size (gravity segregation) and charge (space charge repulsion). For the experiments reported here the charge and mass values were measured for each sensor allowing the calculation of charge to mass ratio (Q/M). In addition, size distribution and surface analyses were carried out for representative samples of the powder components. Data are presented for several types of polymer powders (volume mean diameter <100 μm), with and without extraparticulate additives. The results, in all but one of the cases reported, show that even though the net charge may be positive or negative the fine particles show a negative charge and the coarse particles positive. These results are compared under several possible hypotheses