Bio-based and recyclable materials are currently of high interest. At present, multilayer packaging materials are not economically recyclable and are often not biodegradable or bio-based. However, many food packaging solutions utilise multilayer structures to achieve the mechanical and barrier properties needed to protect and maintain the shelf-life of the packaged goods.

The main objective of D3.1 is to develop a whey protein-based coating to increase oxygen barrier properties. Whey protein-based coatings have previously been identified as an alternative to petrochemical EVOH barrier material. As very high amounts of the annual European production of whey protein are discarded, it is considered a non-direct food competing source. The use of a whey protein-based interlayer in multilayer structures has the added benefit of facilitating enzymatic delamination, allowing material separation of the multilayer structure and subsequent re- or upcycling of the recovered materials. 

Several whey protein coating formulations, varying in protein supplier, plasticizer and plasticizer concentrations, were evaluated concerning their water vapour and oxygen barrier properties. The best performing coating formulation was applied to different polymer substrates, resulting in a coating thickness of approx. 7 and 15 µm. To further improve the barrier properties, a nanoscale aluminium layer was coated onto the protein layer using physical vapour deposition. This approach has the advantage of enabling enzymatic separation of the metal layer from the polymer substrate at the end of life for subsequent re- or upcycling.

Further, a chemical fatty acid grafting process was investigated for PLA substrates. Fatty acid grafting is used to chemically modify a substrate surface at nanoscale by grafting a monomolecular layer of fatty acids onto a substrate surface. This allows a rather hydrophilic surface to be transformed into a hydrophobic surface, resulting in increased liquid repellency.