Factors That Influence the Efficiency of a Propeller-Type Tribocharging Device for Granular Plastics

Abstract

This work is focused on the experimental study of a new propeller-type tribocharging device specifically designed to operate in conjunction with an electrostatic separator for mixtures of granular insulating materials. The device consists of two coaxial aluminum propellers rotating in a polyvinyl chloride (PVC) pipe; it has two control variables: the material feed-rate and the rotation speed of the propellers. Virtual instrumentation using LABVIEW software is used for measuring the mass and the electric charge of the tribocharged samples of four types of polymers: polypropylene (PP); high impact polystyrene (HIPS); high-density polyethylene (HDPE); and PVC. In accordance with the sign and the magnitude of the charge/mass ratio, the four polymers are arranged in a triboelectric series, starting from the negative polarity: PVC-HDPE-PP-HIPS. The effectiveness of the tribocharging process is validated by using a free fall electrostatic separator. The best results (purities and recoveries higher than 90%) are obtained in the case of PVC/HIPS granular mixtures.