Modified Roll-Type Electrostatic Separator for the Processing of Polymer Mixtures Containing Brominated Flame Retardants

Abstract

The aim of the present paper is to study the efficiency of a new configuration of a roll type electrostatic separator in selectively sorting granular polymers containing brominated flame retardants (BFRs) from the same BFR-free polymers. The peculiarity of this configuration is that the “standard” grounded roll electrode is covered by a thin layer of insulating material, which is charged by corona discharge at a polarity opposite to that of the static electrode, to increase the intensity of the electric field in the active zone of the separator. The study was conducted on a mixture composed of equal quantities of BFRs-containing Polypropylene (PP) and BFR-free PP mm-size granules. The mixture was first tribocharged in a fluidized bed device, the walls of which were made of PS, and was then introduced in the corona-charged-insulating-roll-type electrostatic separator, to be selectively sorted under the action of electrical and mechanical forces. The best separation results were obtained in the case where the high-voltage static electrode was connected to a positive DC power supply and the insulating-roll-electrode was charged using a negative corona discharge. With this configuration, when mixed with PP with granules containing 40000 ppm of Br, 70% of the BFR-free PP granules were recovered in a concentrate having a purity of about 80%. The outcome of the electrostatic separation was even better, with purities approaching 93%, for mixtures composed of 50% BFR-free PP and 50% PP granules containing 2000 ppm of Br.