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Plasma Surface Modification of fine Powders in the Afterglow of an Atmospheric Pressure Dielectric Barrier Discharge

English title Powders in the Afterglow of an Atmospheric Pressure Dielectric Barrier Discharge
Applicant Rudolf von Rohr Philipp
Number 141086
Funding scheme Project funding (Div. I-III)
Research institution Institut für Verfahrenstechnik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Chemical Engineering
Start/End 01.05.2012 - 30.04.2015
Approved amount 202'776.00
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Keywords (5)

Wettability; Flowability; Atmospheric Pressure Plasma; Dielectric Barrier Discharge ; Particle Treatment

Lay Summary (English)

Lead
Lay summary

About 60% of all products in the chemical and pharmaceutical industry are in the form of fine-grained powders. Two main difficulties are often encountered while handling particulate products regarding the surface properties of powders. One problem is the low wettability of powders (e.g. polymer powders), which makes it difficult to build stable emulsions or pastes out of these powders without adding environmentally harmful surfactants. The second problem regards the flow behaviour of fine grained powders. Powders often own a low flowability, which leads to malfunction of equipment due to clogging and wall-deposition in various apparatus.

While conventional methods to overcome these unfavourable powder properties are costly and time-consuming, a promising concept has recently be developed which applies so called non-thermal plasmas to modify the surface properties of powders. A non-thermal plasma is an ionized gas, which contains charged particles like electrons and ions, but also neutral species whereat the overall gas temperature stays at a low level. Chemical reactions occurring in the plasma result in the formation of radicals and excited species which can induce changes on a surface exposed to the plasma. Hence, a plasma process allows to change the surface properties of a particles without affecting the powders bulk properties.

Oxygen containing plasmas lead to the formation of polar groups on the particles surface which results in a better wettability of the treated powder. If a silicon containing monomer is introduced into the discharge the formation of nanoparticles is favoured. These nanoparticles are attached to the powders surface and act as spacers between the single particles, which leads to an increased flowability. Up to now, mainly plasmas ignited at low pressure levels are investigated for the surface modification of fine powders. To avoid expensive vacuum equipment, for example pumps and load locks, we investigate a plasma at atmospheric pressure, a “dielectric barrier discharge”, in terms of powder treatment.

Within the scope of this project we will firstly investigate the atmospheric pressure dielectric barrier discharges with spectroscopic methods to examine which kind of species is produced in the plasma. Later on we will analyse plasma treated particle surfaces by chemical and microscopic methods. This approach shall lead to a process which allows a continuous treatment of powders at atmospheric pressure.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Plasma afterglow treatment of Polymer Powders: Process parameters, wettability improvement, and aging effects
Gina Oberbossel Christian Probst Vito Roberto Giampietro Philipp Rudolf von Rohr (2017), Plasma afterglow treatment of Polymer Powders: Process parameters, wettability improvement, and aging effects, in Plasma Processes and Polymers, 14(3), 1600144.
Contact Angle Decay Model to Study Plasma Afterglow Activation of Polymers
Gina Oberbossel Serge Zihlmann Christian Roth Philipp Rudolf von Rohr (2016), Contact Angle Decay Model to Study Plasma Afterglow Activation of Polymers, in Plasma Processes and Polymers, 13(9), 937-945.
Polymer Powder Treatment in Atmospheric Pressure Plasma Circulating Fluidized Bed Reactor
Oberbossel Gina , Guntner Andreas , Kundig Lukas, Rotch Christian, von Rohr PR (2015), Polymer Powder Treatment in Atmospheric Pressure Plasma Circulating Fluidized Bed Reactor, in Plasma Processes and Polymers , 12(3), 285-292.

Collaboration

Group / person Country
Types of collaboration
Dr.Christophe Hollenstein, EPFL Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
International Symposium on High Pressure Low Temperature Plasma Chemistry 2014 Talk given at a conference Powder Surface Activation in an Atmospheric Pressure Circulating Fluidized Bed Plasma Reactor 2014 21.09.2015 Zinnowitz, Germany Oberbossel Gina;
International Symposium on Plasma Chemistry 2015 Talk given at a conference Multichannel Reactor Optimization for the Activation of fine-grained Polymer Powders 05.07.2015 Antwerp, Belgium Oberbossel Gina;
International Symposium on Plasma Chemistry 2013 Talk given at a conference Influence of effective discharge power on polymer powder treatment in atmospheric pressure plasmas 04.08.2013 Cains, Australia Oberbossel Gina;


Abstract

Powder is a predominant product form in the chemical and pharmaceutical industry. Classical handling problems of fine-grained powders include poor wettability (e.g. of polymer powders) and poor flowability of cohesive powders. Hence, particle surface modification processes to overcome these disadvantages, attract increasing attention.Whereas conventional methods are costly and time-consuming, a promising concept has recently been approached in our institute, which applies a low-pressure plasma to modify the surface properties of powders. An oxygen containing plasma allows the incorporation of polar groups on the powders surface, which leads to an increased wettability of the treated powder. By introducing a organosilicon precursor into the plasma nanoparticles are formed and simultaneously attached to the powder particles. The resulting increase in nanoscale surface roughness of the powder particles reduces the attractive, interparticle van der Waals force and thus improves the flowability of the powder. The respective plasma process requires tens of milliseconds instead of hours as in conventional methods. However, the use of low pressure environment to sustain the plasma implies severe drawbacks such as high capital and running costs of vacuum equipment and clogging due to particle-plasma interactions.We therefore propose a non-thermal atmospheric pressure barrier discharge or its reactive afterglow for the treatment of powders. The expected high complexity of the plasma-physical and chemical processes necessitates first to understand transport phenomena of activated molecules from their origin in the plasma to the powder treatment region. Therefore infrared absorption spectroscopic measurements shall be performed in both the discharge and its afterglow. They will allow to identify the density of reactive species in the plasma and its afterglow and their dependence of process parameters. Experiments with an oxygen containing plasma will be conducted to improve the wettability of powder particles. In a next step a precursor will be introduced to the discharge to favour the formation of nanoparticles and their subsequent deposition on the powder particles. The significance of the proposed research is obvious:Fundamental theoretical and experimental investigations will lead to new process techniques for the continuous surface modification of powders by an atmospheric pressure plasma.
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