During the project, twelve different plasma devices with a total of eight different high voltage power supplies were successfully developed, implemented, characterized, and tested.
The adjustment of plasma pre-treatments for optimized wetting or liquid uptake were more complex on more levels than expected. In particular, previously unknown effects were observed, indicating influences by plasma surface treatment deeper inside the work pieces than previously reported. Changes in moisture content, conductivity, and dielectric parameters as well as with an apparent impact on the modulus of elasticity, which were found to occur at least 10 – 100 µm deep inside the material. In addition to that, these changes of substrates’ properties have an influence on the plasma parameters during the ongoing surface treatments. Although not apparent in chemical composition through infrared spectroscopy, these effects have strong implications on how to implement processes for functionalization of wood surfaces by plasma treatments, while also rendering possible additional potentials for applications, e.g. in microwave drying of wooden work pieces.
The preliminary results on plasma curing of liquid precursors were carried out in a closed reactor setup. For the envisioned applications, however, discussions with the mentor as well as with potential industrial users revealed that a closed batch reactor did not come into account. Despite testing various kinds of non-thermal plasma, no working solution for curing of precursor formulations in an open system was found. Instead, the plasma led to such enhanced desorption or evaporation even for the larger molecules, that plasma-induced reactions were not successful.
However, the works led to a new, innovative technical solution for conventional plasma treatments. A critical parameter during plasma treatments is the precise control and the repeatability of the working distance or discharge gap. Typically, this is achieved through elaborate positioning systems and includes additional safety mechanisms. It is, however, problematic for work pieces with changing dimensions or an unsteady feed mechanism. Based on the experiences with other plasma devices, the novel solution utilizes a double- or multiple-lever system that mechanically maintains the correct work distances without the need of an external control system. This "PlasmaSwing” was implemented and tested during the project, and a patent application was filed.
