Effect of storage at different levels of relative humidity of ambient air on the tribo-electrostatic separation of granular plastics containing brominated flame retardants

Abstract

The aim of the present work is to investigate the impact of storage conditions, and more specifically of the relative humidity ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RH</i> ) of ambient air, on the triboelectric charging and electrostatic separation of granular insulating mixtures containing brominated flame retardants (BFR). The study was carried out on two model granular mixtures consisting in equal quantities of Polypropylene (PP) / Polyethylene (PE) particles either BFR-free or containing 4.7% of BFR, in mass (i.e., 40000 ppm of bromine). After being stored for 24 hours either in a climatic chamber ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RH</i> = 30 %, 50 %, 70 %, 20°C) or in ambient air ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RH</i> = 56.5% ± 1.5%; 20°C ± 2°C), the plastic particles were tribocharged in a fluidized bed device the walls of which were made of polystyrene (PS). Then they were introduced in roll type electrostatic separator to be selectively sorted. The results showed a slight difference between the different cases studied, best separation results were obtained for mixtures stored at controlled humidity of 50% or under ambient conditions <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RH</i> 55 % to 58%, at temperatures ranging between 18°C and 22°C.