Dielectric Barrier Discharge Treatment of Granular Plastic Mixtures in View of Their Triboelectrostatic Separation

Abstract

Successful electrostatic separation of granular plastic mixtures is strongly conditioned by the effective triboelectric charging of their constituents. The aim of this article is to demonstrate that appropriate exposure to a dielectric barrier discharge (DBD) at atmospheric pressure changes the triboelectric properties of plastics and favors their separation under the action of electric field forces. The experiments were conducted with nine different plastics originating from waste electric and electronic equipment [acrylonitrile butadiene styrene, high-impact polystyrene (HIPS), polycarbonate (PC), Cristal PC, polyethylene (PE), polypropylene (PP), polystyrene (PS), Cristal PS, and polyvinyl chloride (PVC)] using a rotating cylinder tribocharging device and a roll-type electrostatic separator. The cylinder of the device was made of either high-density PE or PVC. The comparison between the results of triboelectric charging and electrostatic separation of DBD-exposed and unexposed granules pointed out the effectiveness of nonthermal plasma treatment of the plastic wastes. Most of DBD-exposed granules acquire a negative charge, whereas the majority of the plastics considered in this study got positively charged, if not pretreated in the nonthermal plasma reactor. The modifications the DBD exposure induces on the triboelectric series highly affect the electrostatic separation of six different mixtures (PE–HIPS, PE–PP, PE–PVC, PP–HIPS, PP–PVC, and PVC–HIPS).