DEVELOPMENT OF A CONTINUOUS NANOPARTICLE COATING WITH ELECTROSPRAYING

Coating of micron-sized particles (host particles) with nanoparticles can result in modifying the surface properties of host particles leading to various applications. This work presents a novel concept of combining the electrospraying of nanoparticles onto the charged particles entrained out of the fluidized bed for developing a continuous coating process. By controlling the processes to effectively charge and contact particles using electric forces, we are able to fine-tune the properties of the obtained nano-coated particles

Twenty-First Century Research Needs in Electrostatic Processes Applied to Industry and Medicine

From the early century Nobel Prize winning (1923) experiments with charged oil droplets, resulting in the discovery of the elementary electronic charge by Robert Millikan, to the early 21st century Nobel Prize (2002) awarded to John Fenn for his invention of electrospray ionization mass spectroscopy and its applications to proteomics, electrostatic processes have been successfully applied to many areas of industry and medicine. Generation, transport, deposition, separation, analysis, and control of charged particles involved in the four states of matter: solid, liquid, gas, and plasma are of interest in many industrial and biomedical processes. In this paper, we briefly discuss some of the applications and research needs involving charged particles in industrial and medical applications including: (1) Generation and deposition of unipolarly charged dry powder without the presence of ions or excessive ozone, (2) Control of tribocharging process for consistent and reliable charging, (3) Thin film (less than 25 micrometers) powder coating and Powder coating on insulative surfaces, (4) Fluidization and dispersion of fine powders, (5) Mitigation of Mars dust, (6) Effect of particle charge on the lung deposition of inhaled medical aerosols, (7) Nanoparticle deposition, and (8) Plasma/Corona discharge processes. A brief discussion on the measurements of charged particles and suggestions for research needs are also included

A methodology for tribocharger design optimisation using the Discrete Element Method (DEM)

Tribocharger design optimisations presented in the literature are based typically on experimental investigations. While this approach is useful and necessary to evaluate the performance of a design, experimental investigations are limited to studying a finite matrix of parameters. Computational approaches, such as the discrete element method (DEM), offer greater flexibility, however they have not been used previously for tribocharger design optimisation. This work presents a novel approach using the DEM to study the effect of different tribocharger designs on the charging process using particle–wall and particle–particle contact areas as proxies for charge transfer. The bulk sample charge output from the model are compared with bulk charges measured experimentally, showing good agreement. Furthermore, a method to predict approximately the charging behaviour of complex mixtures from linear combinations of the simulation outputs of single species, single size particle samples is presented, demonstrating good agreement

Properties of Tailored Granular Media

The macroscopic behavior of granular media is determined by interactions at the grain scale. While some phenomena in granular media can be explained by hard sphere models, experiments always deal with friction, van-der-Waals forces, liquid bridge formation and tribocharging. In how far these interactions determine the macroscopic behavior and the relative strength of each interaction in a real experiment are often difficult to estimate. In this thesis, we investigate how changes at the surfaces of granular spheres can influence the macroscopic behavior of a granular medium. In a first experiment, we measure the rheological properties of surface modified granular particles. Such modifications necessarily influence multiple factors at once and so we measure the influence of the surface modifications on friction, wettability and triboelectric charging behavior and then correlate the changes at the grain scale to the macroscopic behavior. In a second experiment, we investigate in how far charging effects due to tribocharging can determine the packing structure of a granular packing. In the context of controlling the triboelectric effect, we investigate the stochastic nature of exchanged charges in collisions of granular particles and investigate the effect of surface treatments on triboelectric charging behavior. We show that triboelectric charging can indeed define the packing structure and lead to ordered structures in which electrostatic potential is minimized. The effect of boundary conditions is also investigated. Finally, we show that wall friction and piston shape influence the force propagation and displacements in a two dimensional granular medium

A review of factors affecting electrostatic charging of pharmaceuticals and adhesive mixtures for inhalation

Pharmaceutical powders are typically insulators consisting of relatively small particles and thus they usually exhibit significant electrostatic charging behaviours. In the inhalation field, the measurement of electrostatic charge is an imperative stage during pharmaceutical formulation development. The electrostatic charge is affected by the interplay of many factors. This article reviews the factors affecting the electrostatic charging of pharmaceutical powders with a focus on dry powder inhalations. The influences of particle resistivity, size distribution, shape distribution, surface roughness, polymorphic form and hygroscopicity, as well as the effects of moisture uptake, environmental conditions, pharmaceutical processing (i.e., milling, sieving, spray drying and blending), and storage on the electrostatic charge behaviours of pharmaceuticals, with focus on inhalation powders, were reviewed. The influence of electrostatic charge on the performance of dry powder inhaler formulations in terms of drug content homogeneity, the passage of drug through the inhaler device, drug-carrier adhesion/detachment, and drug deposition on the respiratory airways were discussed. The understanding gained is crucial to improving the safety, quality, and efficiency of the pharmaceutical inhalation products

Modelling and experimental validation of tribocharging for space resource utilisation (SRU)

Space Resource Utilisation (SRU) technology will enable further exploration and habitation of space by humankind. For example, oxygen produced \textit{in situ} can be used as the oxidiser in rocket propellant, or for life support systems. The production of oxygen on the Moon can be achieved through the thermo-chemical reduction of the lunar soil, also known as regolith. All reduction techniques require a consistent feedstock from this mix of fine mineral particles to produce oxygen reliably and consistently. The preparation of this feedstock, known as beneficiation, is a critical intermediate stage of the SRU flowsheet, however it has received little research attention relative to the preceding excavation, and the subsequent oxygen production stages. Triboelectric charging and free-fall separation are attractive technologies for mineral beneficiation as they offers low mass, low power, and low mechanical complexity compared to other approaches. Tribocharging is a process by which particles (conductors, semi-conductors, and insulators) acquire charge through frictional rubbing and subsequent separation. Previous experimental studies have tested different designs of tribocharging apparatuses for terrestrial and space applications, however charge transfer modelling methods have not been employed to optimise design parameters. Furthermore, whilst modelling of the triboelectrification process has been presented in the literature using the discrete element method (DEM), these models often depend on poorly quantified or ill-defined parameters, such as an effective work function for insulating materials. Previous studies have also been restricted to either 2D or 3D domains and have not considered the impact of this on the performance of the models. To address these knowledge and research gaps, the objectives of this thesis are as follows: \begin{enumerate} \item Develop a novel tribocharge modelling approach based on the discrete element method that de-emphasises the poorly-defined quantities found in the high-density limit approach that has been demonstrated previously; \item Determine the suitability of modelling tribocharging in 2D and 3D; \item Validate this novel tribocharge modelling method by comparing simulation outputs and experimental data; \item Present and validate a new DEM-based method for tribocharger design optimisation; and, \item Evaluate experimentally the impact of an optimised tribocharger design on the performance of an electrostatic separator using standard mineral processing criteria. \end{enumerate} A straightforward experimental method to quantify key tribocharging model parameters, namely the charge transfer limit, $\Gamma$, and the charging efficiency, $\kappa_c$, is presented herein. These parameters are then used in both 2D and 3D DEM charge transfer simulations (particle-particle and particle-wall interactions; single and multiple particles and contacts) to evaluate the suitability of faster 2D models. Both the 2D and 3D models were found to perform well against the experimental data for single-contact and single-particle, multi-contact systems, however 2D models failed to produce good agreement with multi-particle, multi-contact systems. A novel DEM-based approach for tribocharger design optimisation using particle-wall and particle-particle contact areas as proxies for charge transfer is demonstrated. This optimisation method is used to design an optimal tribocharger for use under terrestrial conditions. The novel tribocharge modelling approach was then applied to the optimised charger design. This design was then built and validated experimentally, with good agreement found between the model outputs and experimental data. The optimised terrestrial design was then employed to study the charging behaviour of pure silica and ilmenite, as well as binary mixtures of silica and ilmenite, and samples of lunar regolith simulant JSC-1. Ilmenite was used because it is a target mineral for oxygen production from the lunar regolith, and silica was used because of its position in the triboelectric series relative to ilmenite. The optimised tribocharger design affected significantly the movement of pure ilmenite in the electrostatic field, despite a negligible change in bulk charge. Experimental results from the binary mixtures indicate that ilmenite recovery is independent of initial ilmenite concentration and can be predicted from the mass distribution of pure ilmenite samples. For JSC-1, the tribocharger was found to increase the density of the material in certain collectors. This thesis presents new modelling approaches for both tribocharging and tribocharger design optimisation. These techniques will facilitate ultimately the development of beneficiation technologies for SRU. The use of these modelling methods should increase confidence in the performance of tribocharger designs proposed for future SRU missions to the Moon.Open Acces

A Review of Sorting and Separating Technologies Suitable for Compostable and Biodegradable Plastic Packaging

As a result of public pressure and government legislation to reduce plastic waste there has been a sharp rise in the manufacture and use of alternatives to conventional plastics including compostable and biodegradable plastics. If these plastics are not collected separately, they can contaminate plastic recycling, organic waste streams, and the environment. To deal with this contamination requires effective identification and sorting of these different polymer types to ensure they are separated and composted at end of life. This review provides the comprehensive overview of the identification and sorting technologies that can be applied to sort compostable and biodegradable plastics including gravity-based sorting, flotation sorting, triboelectrostatic sorting, image-based sorting, spectral based sorting, hyperspectral imaging and tracer-based sorting. The advantages and limitations of each sorting approach are discussed within a circular economy framework

PET and PVC separation with hyperspectral Imagery

Traditional plants for plastic separation in homogeneous products employ material physical properties (for instance density). Due to the small intervals of variability of different polymer properties, the output quality may not be adequate. Sensing technologies based on hyperspectral imaging have been introduced in order to classify materials and to increase the quality of recycled products, which have to comply with specific standards determined by industrial applications. This paper presents the results of the characterization of two different plastic polymers—polyethylene terephthalate (PET) and polyvinyl chloride (PVC)—in different phases of their life cycle (primary raw materials, urban and urban-assimilated waste and secondary raw materials) to show the contribution of hyperspectral sensors in the field of material recycling. This is accomplished via near-infrared (900–1700 nm) reflectance spectra extracted from hyperspectral images acquired with a two-linear-spectrometer apparatus. Results have shown that a rapid and reliable identification of PET and PVC can be achieved by using a simple two near-infrared wavelength operator coupled to an analysis of reflectance spectra. This resulted in 100% classification accuracy. A sensor based on this identification method appears suitable and inexpensive to build and provides the necessary speed and performance required by the recycling industry

Study on Developments of Processes for Powder Coatings

Powder coating, which utilizes polymer resin based powder, is a relatively young technology for decorative and protective purposes. It was first developed in the early 1950s and gradually grew into automotive finishes. Compared to conventional liquid coating, powder coating is an environmentally friendly technology, given that there is no emission of harmful solvent throughout the entire operating process. It is also much more efficient, economical and energy saving as a result of the capability to reuse all the powder. However, there are still some problems in the powder coating process limiting its application. This thesis focused on studying some key aspects of the manufacturing and application processes of both coarse powder and fine powder. Several new techniques were developed during the process. The study started with an investigation of powder coating manufacturing processes. Most of the production is aiming at maximizing the productivity, while the produced powder has a wide particle size distribution, leading to a poor surface condition. In order to narrow the particle size distribution, a new design of classifying cyclone for an air classifying mill (ACM) with a reversed air inlet was studied. Experimental results indicated that this novel cyclone design could effectively reduce the span of the particle size distribution, without deteriorating the collection efficiency compared to conventional cyclones. In addition, the spraying properties of powder coatings were investigated during electrostatic spraying. In order to overcome the Faraday Cage effect, a modified corona spray gun with a multi-electrode design supplied by an alternating charging pattern was invented. Experimental results demonstrated that the Faraday Cage effect could be significantly mitigated by using the new spray gun at various gun voltages. Besides, the new design of spray gun could provide higher transfer efficiency compared to its conventional counterpart. Moreover, this study also improved the powder coating processing technique involving metallic pigments. To achieve better bonding between metallic pigments and powder coating particles, a liquid bonding agent (bonder) was introduced into the blending process. It was found that the concentration of metallic pigments changed minutely from the pre-sprayed and post-sprayed powder, indicating that the recycled powder could be reused. Therefore, this new bonding method of utilizing liquid bonder could provide a strong affinity between the powder coating and metallic pigments so as to prevent separation of the two materials during spraying. At the end, a pre-heating method of applying powder coating onto thermoplastic substrates, which helps powder deposition and adhesion onto plastic substrates, was studied. Three widely used powder coatings have been tested for this method. The coating films were evaluated by both visual inspection and instrumental measurements. It was found that this new processing method could provide a smooth surface as well as a strong adhesion to the difficult substrate. Furthermore, for the purpose of protecting the thermoplastic substrate from deformation during the curing process, a UWO low-cure method was applied to these three powder coatings. Compared with commercial low-cure powder, the UWO low-cure coatings perform better in a few aspects. The discoveries and analysis in this thesis work are contributing to powder coating development. Several original techniques have been invented in this study and they could provide a good guideline for future work of modern powder coating technology