Triboelectrification of granular insulating materials as affected by dielectric barrier discharge (DBD) treatment Abdelkader Nadjem a, b , Miloud Kachi a, * , Fethi Bekkara b , Thami Zeghloul b , Lucian Dascalescu b a Electrical Engineering Laboratory, 8 May 1945 University, 24000 Guelma, Algeria b PPRIME Institute, UPR 3346, CNRS - University of Poitiers - ENSMA, 4 Varsovie Avenue,16021 Angoul^ eme, France article info Article history: Received 8 September 2016 Received in revised form 18 November 2016 Accepted 7 December 2016 Keywords: Triboelectricity Dielectric barrier discharge (DBD) Granular material Electric charge Electrostatic separation abstract The aim of this paper is to point out the influence of dielectric barrier discharge treatment on tri- bocharging of granular insulating materials. Particles of Polyvinyl Chloride (PVC) and Polypropylene (PP) were subjected to an AC dielectric barrier discharge (DBD) plasma treatment in ambient airprior to tribocharging in a vibratory device. The charge to mass ratio was measured for treated and untreated materials. Electrostatic separation of a mixture of granular materials (PVC and PP) to measure the effectiveness of DBD treatment was evaluated by processing treated and untreated PVC/PP granular mixtures in a free-fall electrostatic separator. The obtained results clearly indicate that DBD has the capability to influence surface charging proprieties of polymer granular materials. In case of short treatment time, typically less than 3 s, a marked increase in the charge to mass ratios was observed for both PVC (about 35%) and PP (roughly 45%). In the same way, the quantity of DBD-treated materials, recovered after electrostatic separation, was increased by about 104% and 30% for PVC and PP, respec- tively, as compared to untreated case. The DBD treatment time is a key factor to increase the tribo electric effect. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Triboelectricity is one of the earliest observed, but also less understood electrostatic phenomena [1e3]. Until recently, tribo- electrification of insulating materials was perceived mainly as a source of electrostatic hazard [4e6]. Nowadays, the triboelectric effect is more and more employed as a charging mechanism in several electrostatic applications, such as: separation of polymer materials [7e9], energy harvesting [10,11], triboelectric based sensors [12,13]…etc. In such applications, the charge acquired by the materials has a major influence on the outcome of the process. Therefore, it is very important to enhance the tribocharging capa- bility of the processed materials. Tribocharging occurs when two different materials are sepa- rated after having exchanged electric charges during their contact [14]. In the process, one material acquires positive and the other negative charges. Despite the important number of studies devoted to triboelectricity, the mechanism of charging by contact (and friction) between insulators seems to be still unclear. Indeed, several issues are still poorly understood, like the nature of the charge carriers exchanged during contact, the role of friction, of contact pressure, of ambient conditions and so on. In this day, tri- boelectrification of insulators is tentatively explained by three mechanisms: electron transfer [15], ion transfer [16] and transfer of charged material between the bodies in contact [17]. Understand- ing these mechanisms would help to improve, or inversely elimi- nate, the triboelectric effect. The electrostatic separation of granular insulating mixtures is the result of the combined action of mechanical and electric forces [18]. Therefore, the triboelectric charge carried by the granules should be as high as possible so that the electric Coulomb force could overcome the mechanical and gravitational forces and consequently better separate the constituents of the mixture. Pre- vious carried studies on electrostatic separators have already tried to improve the tribocharging devices and optimize their operation. One solution, for instance, is to increase the charging time and air speed in the case of fluidized bed devices [19e23]. However, the possibilities offered by the adjustment of such parameters are * Corresponding author. E-mail address: miloud.kachi@gmail.com (M. Kachi). Contents lists available at ScienceDirect Journal of Electrostatics journal homepage: www.elsevier.com/locate/elstat http://dx.doi.org/10.1016/j.elstat.2016.12.017 0304-3886/© 2016 Elsevier B.V. All rights reserved. Journal of Electrostatics 86 (2017) 18e23