Comparison between the surface-electric-potential characteristics of tribo- and corona-charged polymers

The ability of polymers to acquire and retain electrostatic charges is valued in designing new equipment like electrostatic separators, electret filters and powder coating devices. Several recent studies have pointed out the beneficial effect of electric charges on the lubricated contacts. The aim of this paper is to compare two physical mechanisms of electric charging of polymers: triboelectric effect and corona discharge. The experiments are performed with 5-mm-thick samples of polystyrene (PS), poly-vinyl-chloride (PVC) and polypropylene (PP). The cartography of the electric potential is made using the capacitive probe of an electrostatic voltmeter. The tribocharging is done by back and forth movement of two polymer plates in conformal contact with each other (speed: 7 to 30 mm/s; constant normal force: 2 N). Uniform corona charging is performed by moving the sample in the space charge zone generated by a wire-type high-voltage electrode, used in a triode configuration, with the potential of the grid electrode set at 0.5 kV, 1 kV and 2 kV. The electric potential at the surface of tribo-charged polymers is less uniform and decays faster than that of corona-charged samples.