Environmentally harmful plastic waste has increased continuously in Germany in recent years. Packaging generates a particularly large amount of waste. Coatings for paper packaging based on plant-based ingredients could provide a sustainable replacement in the future. In the BioPlas4Paper project, researchers at the Fraunhofer Institute for Surface Engineering and Thin Films IST and their partners used plasma polymerization to create water-repellent barrier coatings based on plant substances on paper, thereby improving the material's resistance to weathering. The plasma is generated using a plasma source by ionizing gas between two rotationally symmetrical electrodes to which high voltage is applied. What is new is the geometric arrangement of the electrodes and the way in which the aerosol is introduced and the plasma is ignited. The combination of these measures results in an innovative concept that the researchers developed specifically for the project, so that the effects of the ambient air are reduced to a minimum under atmospheric pressure, even at higher coating speeds, and the results are consistent and reproducible. Due to the roughness of the paper surface, the ambient air is swirled at high processing speeds, which changes the plasma properties. These harmful influences can be avoided with the IST concept. The plasma source is brought close to the paper surface and thus completely displaces the ambient air. Plasma temperatures of around 70 degrees are used to ensure that the paper itself, the bio-based precursor molecules and the properties of the plasma polymers produced are not adversely affected. The project was able to prove that biobased materials can be reproducibly and homogeneously deposited or separated using plasma. Very good hydrophobic layers could be achieved with olive and chia oil, for example. One application example is moving boxes, which can be exposed to rain for longer periods without softening thanks to the hydrophobic layers.
