Two stage electrostatic separator for the recycling of plastics from waste electrical and electronic equipment

The aim of study was to evaluate the effectiveness of a new facility for recycling of plastics from granular waste electrical and electronic equipment. The installation consists of two sections, the products of a first tribo-aero-electrostatic separator being subsequently treated in two free-fall electrostatic separators. The tests were performed on a mixture of polycarbonate (PC) and polyamide (PA). Analysis of the purity of the products obtained was performed using a program of image processing in MATLAB. Products of very high purity (roughly 95% for both PC and PA) were obtained at a recovery rate higher than 70%.     

Triboelectrification of granular insulating materials as affected by dielectric barrier discharge (DBD) treatment

The aim of this paper is to point out the influence of dielectric barrier discharge treatment on tribocharging 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, respectively, as compared to untreated case. The DBD treatment time is a key factor to increase the tribo electric effect.     

Flexoelectric effect driven colossal triboelectricity with multilayer graphene

Converting mechanical deformation from surrounding environment into detectable electrical signals remains one of the most attractive fields due to its potential applications in sustainable energy harvesting, self-powered sensors, and others. Presently, deformation energy is harvested by generating voltage/current through bending/twisting of piezoelectric materials, but its recyclability is limited in number. In contrast, polarization is generated in all known insulators/semiconductors due to elastic strain gradient, which offers unique electromechanical coupling and in turn, could generate significant potential differences to drive charge transfer. Here, we demonstrate that extremely high direct current with density of 28 × 10⁶ A m⁻² is generated without need of any external power supply by applying pointed force using conductive-atomic force microscope (cAFM) tip on multilayer graphene/substrate (SiO₂, Si, glass). Further, the ramp-dependent time-resolved current is measured at a localized point, which indicates that pointed force-induced flexoelectric potential differences are the main driving factor to utilize mechanoelectrical coupling and in turn generate high current density. This research work provides a new strategy to utilize the flexoelectric effect to utilize electromechanical coupling to generate giant energy harvesting, which will have a potential impact on the various multiple fields including smart devices, materials, and even a fundamental understanding of physics.     

Effect of particle size on the tribo-aero-electrostatic separation of plastics

Numerous research studies have been made on the electrostatic separation of granular insulating materials, with many industrial applications in the area of waste electric and electronic equipment (WEEE) recycling. However, very few investigators have studied the separation of finely-ground matter (i.e., granule diameter < 1 mm), in relation with applications in mineral processing, or in food industry. The aim of this work is to evaluate the effect of particle size on the selective sorting of fine particles in a two-rotating-disks-type tribo-aero-electrostatic separator. The experiments are carried out on a synthetic mixture composed of 50% Acrylonitrile Butadiene Styrene (ABS) and 50% Polystyrene (PS) particles of size 250 to 2000 microns. The performance of this separator is evaluated by setting up a measurement system that enables the continuous and simultaneous recording of the charges and the masses of the separated products. The conclusions of this study will serve at the optimum design of an industrial electrostatic separator for the recycling of micronized plastics from WEEE.     

Numerical simulation of the continuous operation of a tribo-aero-electrostatic separator for mixed granular solids

Numerical simulation has proved to be a powerful tool in the research and development of new electrostatic processes. In a previous paper, the authors have introduced a simple mathematical model for simulating the outcome of a novel tribo-aero-electrostatic separation process for binary mixtures of granular materials. The mathematical model assumed that the probability of a granule to be separated can be expressed as a function of the number of impacts with granules belonging to the other class of materials. The process is characterized by the fact that the charging of the granules is produced in a fluidized bed device, in the presence of an electric field. The aim of the present paper is to simulate the continuous operation of such a device at various feed rates. The evolution in time of the mass of granules collected at the electrodes has been computed for various compositions of the granular mixture. The effect of the walls was taken into account. The computed results were in good agreement with the experiments. They demonstrate that open-loop continuous operation of the separator is possible for a range of feed-rates that depends on the composition of the materials to be separated.     

Facile and low-cost synthesis of flexible nano-generators based on polymeric and porous aerogel materials

Triboelectric nano-generators (TE-NGs) can be utilized as a power supply for wireless systems, sensors, and operators. In this paper, new flexible TE-NGs that use sodium carboxymethyl cellulose (CMC), poly dimethyl siloxane (PDMS), polyvinylidene fluoride (PVDF), poly (4,4′-oxydiphenylene-pyromellitimide) (KAPTON) films and also sugar as a piezoelectric material were developed and are reported. Also, the outputs of NGs made by linear power under a periodic pressure of ~ 0.2 MPa at a frequency of 3 Hz showed that the highest output of NGs are related to PDMS–KATTON, PDMS, PVDF–KAPTON, PVDF, CMC NGs, respectively. It has been also observed that NGs connected in series to each other have a higher output than paralleled NGs so that their voltages increase at higher frequencies. Besides, a significant point is that the NGs are made in a low-cost, affordable, and environmentally-friendly route, which is a superior characteristic with respect to the rest of the NGs.     

Numerical simulation of a tribo-aero-electrostatic separation of a ternary plastic granular mixture

Granular materials, when fluidized by air or other gaseous medium, acquire electrostatic charge by particle-particle and particle-wall collisions. The effectiveness of particle tribocharging achieved with such fluidization process is crucial for establishing the feasibility of electrostatic separation of mixed granular solid wastes in the recycling industry. The aim of the present work is to introduce a simple mathematical model for simulating the outcome of a novel tribo-aero-electrostatic separation process involving mixture of three granular materials. The process is characterized by the fact that the charging of the granules is produced in a fluidized bed device, in the presence of an electric field. The mathematical model in this case assumed that the probability of a granule to be separated can be expressed using the normal distribution law, as a function of the number of impacts with granules belonging to the other classes of materials. The effect of the presence of a third species of particles was taken into account. Thus, it was possible to calculate the evolution over time of the mass of granules separated at the electrodes for different compositions of the granular mixture. The calculated results are in good agreement with the experiments.