Triboelectric Charging of DBD-Treated Granular Plastic Waste Previously-Exposed to Long-Term Action of High-Levels of Ambient Humidity

Dielectric barrier discharges (DBD) are known to change the surface morphology, the surface chemical composition, and the triboelectric properties of the treated polymers. The work presented in this paper was aimed at studying the effect of long-term exposure of high-levels of ambient humidity on the triboelectric charging of DBD treated granular plastics. The experiments were carried out on four types of polymers, ABS, PP, PE and PS, with an average particle size between 4 mm and 6 mm. To study the effects of relative humidity of ambient air, the granules were stored for 72 h in a climatic chamber, disposing of simultaneous humidity and temperature control. The relative humidity was regulated at 82% ± 4%, for a temperature of 19°C ± 1°C. The water content of “humid” granules was measured with a thermal-balance and compared with that of “normal” granules, kept at ambient humidity (46% to 52%), at a temperature of 18°C ± 1°C. The “humid” and “normal” granules were successively exposed to a dielectric barrier discharge (DBD) for 60 s in a custom-designed reactor then charged by triboelectric effect in a multi-cylinder triboelectric device. As expected, the DBD treatment modified the triboelectric behavior of each polymer. The experiments showed that the charge/mass effect of this treatment is different on “humid” and “normal” particles. The study points out the importance of providing appropriate storage conditions (i.e., humidity levels lower than 70%) for the plastic wastes processed by tribo-electrostatic techniques.