Triboelectric Charging of Granular Polymers Previously Exposed to Dielectric Barrier Discharges in Atmospheric Air

The aim of the present article is to study the feasibility of continuous dielectric barrier discharge (DBD) treatment of granular plastic materials in view of improving their triboelectric charging ability, and assessing the effectiveness of associating plasma treatment with the triboelectrostatic separation process. The effects of the following DBD parameters were studied: the amplitude and the frequency of the applied high voltage, the thickness of the dielectric barrier, the distance between the electrodes of the reactor as well as the speed of the conveyor that was used for the transfer of the granular materials though the nonthermal plasma zone. The study was carried out on millimeter-sized polyethylene particles. It was found that the charge of DBD-treated particles increases with the applied high voltage and decreases with the speed of the conveyor. Both the distance between the electrodes and the thickness of the dielectric barrier have a remarkable effect on the charge acquired after DBD treatment. Within the experimental domain of this study, the frequency of the high voltage does not significantly affect the efficiency of the tribocharging process. Under optimal operating conditions given by the first series of experiments, two distinct triboelectrical series were established, one for treated particles and the other for untreated particles, using eight types of granular plastics [acrylonitrile butadiene styrene, polyethylene (PE), polypropylene, polyvinyl chloride, crystalline polycarbonate, polystyrene (PS), high impact polystyrene, and crystalline polystyrene], Finally, an electrostatic separation experiment was carried out on a plasma-treated PE-PS mixture using a roll type electrostatic separator. The results were then compared with those obtained for an untreated mixture. It was found that plasma treatment improved by about 40% the purity and recovery of the sorted products.