Getting post-consumer recyclates safely into high-quality applications such as packaging requires technical finesse. Either all problematic substances must be removed from the material or it must be shielded with a layer of suitable material. In principle, all materials that completely enclose the recyclate and can withstand the application-specific loads are suitable for the second variant. A plasma coating fulfills these requirements. A team of young scientists at IKV in Aachen is working on just such a technology. In an interview with Circular Technology, Ali Cetin, Philipp Alizadeh and Jonas Franke explain what plasma actually is and why the technology is so well suited to shielding recyclates.

Circular Technology: Understandable for laypeople: What is a plasma?

Ali Cetin: Plasma is the fourth aggregate state of matter alongside solid, liquid and gaseous. If the gaseous state of matter is considered, the atoms or molecules are freely movable in the space under consideration. The atoms or molecules in space are electrically neutral, which means that the number of positive protons in the atomic nuclei equals the number of negative electrons in the atomic shells.

If the gas is supplied with sufficient energy – e.g. through electromagnetic radiation – the electrons can detach from the atomic shells, resulting in a mixture of positively charged atoms (ions) and free electrons. Technical plasmas, which typically have a degree of ionization of or , are extremely reactive despite the low proportion of charged particles and enable chemical processes under simple conditions. At room temperature and low pressure, chemical reactions are made possible in remarkable applications such as Plasma Enhanced Chemical Vapor Deposition (PECVD), which can normally only take place at much higher temperatures of a few hundred or thousand Kelvin.

Using PECVD, a gaseous precursor is ionized into a plasma, which then reacts with a substrate surface to deposit thin films.

CT: What does the applied layer consist of?

Jonas Franke: Coatings produced by PECVD can have different chemical and physical compositions depending on the plasma process and the gases used. In such applications, plasma layers are generated which, for example are based on the element silicon. Due to the different process control during layer deposition, glassy silicon-oxide (“_SiOx“) and soft silicon-organic (“SiOCH”) layers, which fulfill different functions, are applied to the plastic surfaces.

CT: Why do you use plasma coatings for recyclate in this application?

Philipp Alizadeh: Plasma-based silicon layers have very good barrier effects against gases such as oxygen or water vapor. The aim of this application is to transfer the barrier effects to a wide range of chemicals that may be contained in the recyclate and may have a negative impact on the filling material.

No influence on recyclability

CT: What are the advantages of shielding recyclates with a layer of virgin material, for example?

Philipp Alizadeh: “The coatings used, which are only a few 10 nm thick, offer an innovative and more efficient solution for recyclates, as they are applied thinly and precisely to the product surfaces by PECVD, so that material consumption is additionally reduced compared to virgin material and the recyclability of the materials used is not affected. This results in a reduction in environmental impact and a reduction in costs compared to the use of new materials. The migration barrier can be tailored to different contaminants.

Safety first

CT: How stable is the layer – is there a risk of it being damaged and substances from the recyclate being transferred to the packaged goods?