Development of multilayer strain-tolerant PECVD gas barrier coatings for plastics using adjustable layer stresses and simulation-based mass transfer studies.

• Applicant: Professor Dr. Rainer Dahlmann
• Subject Area: Plastics Engineering
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 470287198

The equipping of plastics with thin barrier coatings in the packaging sector is again attracting a great deal of attention due to the current recycling rates and the EU Packaging Ordinance (VerpackV). In comparison to conventional multilayer composite systems made of plastic and aluminium or coextruded multilayer systems consisting of different types of plastic, a plastic with a plasma polymer coating remains a monomaterial solution in terms of recycling technology, which allows recycling of only one type. The disadvantage of these coatings is their low ductility, which is due to the highly cross-linked structures. As a result, the industrial use, especially in the field of sheet material, has been limited so far. In the project applied for, multi-layer plasma polymer gas barrier coatings for plastics are to be developed, which retain their barrier effect (e.g. against oxygen and water vapour) at an elongation of 8 to 10 %. The research hypothesis is put forward that the extensibility of individual barrier layers can be increased in particular by adjustable intrinsic and thermal layer stresses, whereby a multilayer barrier system with significantly increased extensibility can be developed. For this purpose, a novel measuring method was developed at the IKV within the framework of the SFB-TR 87, which enables the layer tension on sensors to be monitored and thus adjusted in real time during the coating process. The examination of the ductility is carried out in-situ with the help of a micro-tensile testing module under light and electron microscopes. The evaluation of cracks and layer defects is supplemented by electrochemical measurements (cyclovoltammetry) of the defect surface. In contrast to microscopic examination of the cracks, electrochemistry can be used to check the crack propagation in the different layer layers.The mass transport through the cracked barrier layers and the plastic is modelled with a three-dimensional multi-scale simulation and calibrated with experimental data with knowledge of the crack density. Using the simulation methodology, layer architectures consisting of several layers of barrier and decoupling layer are developed and continuously experimentally investigated. The underlying theory consists of an increase in the ductility of the barrier layers and the extension of the transport path of the gases through cracks in the different layers of the multilayer system (tortuous path model). To produce the layer systems on films made of polypropylene (PP) and polyethylene terephthalate (PET), layer systems with combinations of selected monomers (SiOx/SiNx/SiOx/SiOCH/a-C:H) are produced.

• DFG Programme: Research Grants