Factors Influencing the Triboelectric Charging of Granular Plastics in a New Rotating Multicylinder Type Device

The efficiency of the electrostatic separation of granular plastics wastes depends on the electric charge acquired by the particles in appropriate tribocharging devices. The objective of the present study was the development and functional optimization of new tribocharger design consisting of an assembly of six cylinders, made of polyvinyl chloride (PVC), acryl-methyl butadiene styrene (ABS), or polycarbonate (PC) that can rotate at variable speed and be inclined at a certain angle with respect to the horizontal plane. The performances of the triboelectric charger were evaluated by measuring the charge per mass ratio of the granules collected at the outlet of the device. A first set of experiments involved eight granular polymers, size 2 to 6 mm, originating from waste electric and electronic equipment. The polymers could be arranged in a triboelectric series with respect to the amount of charge acquired in contact to the PVC, ABS, and PC cylinders. A second set of experiments was carried out with polystyrene granules and enabled the choice of the limits of variation of the two factors that were expected to affect the tribocharging: the inclination of the six-PVC-cylinder assembly and its rotation speed. Finally, design of experiments methodology was used for modeling and optimization of the process. The best results were obtained for high rotation speeds and low inclination angles.