Triboelectrostatic Separation 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 for sorting brominated flame retardants (BFR) polymers from BFR-free polymers. The main characteristic of this separator is that the standard grounded rotating roll electrode is coated with a thin film of Polyurethane (PU). A wire-type corona electrode connected to a DC high voltage supply and placed at distance of 35 mm of the surface of the roll was used to charge the PU film at a polarity opposite to that of the static high-voltage electrode. The study was conducted on a granular polymer mixture composed of equal quantities of Polyethylene (PE) containing 40000 ppm of brominated flame retardants (4.7%) and BFR-free PE. The granular mixture to be sorted was first tribocharged in a fluidized bed tribocharger, the walls of which are made of PE, 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 results show that the best separation results are obtained in the case where the high-voltage static electrode is connected to a positive DC power supply and the insulating roll charged with a negative corona discharge, with this configuration 70 % of BFR-free PE can be recovered with a purity of around 80 %.