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.