Sustainability and recyclability are among the main driving forces in the plastics industry, since the pressure on crude oil resources and the environment is increasing. The aim of this research is to develop a sustainable thermoformable multilayer food packaging, based on co-polyesters, which is suitable for hot-fill applications and allows for recycling in a conventional waste stream. As a polymer material for the outer layer, we selected a modified polyethylene terephthalate (PETM), which is an amorphous co-polyester with a high glass transition temperature (±105 °C) and thus high thermal stability and transparency. The inner layer consists of 1,4-cyclohexylene dimethanol-modified polyethylene terephthalate (PETg), which is allowed to be recycled in a PET stream. Multilayers with a total thickness of 1 mm and a layer thickness distribution of 10/80/10 have been produced. To test the recyclability, sheets which contained 20% and 50% regrind of the initial multilayer in their middle PETg layer have been produced as well. The sheet produced from virgin pellets and the one containing 20% regrind in the middle layer showed no visible haze. This was not the case for the one containing 50% regrind in the middle layer, which was confirmed by haze measurements. The hot-fill test results showed no shrinkage or warpage for the multilayer trays for all temperatures applied, namely 95, 85, 75 and 65 °C. This is a remarkable improvement compared to pure PETg trays, which show a visible deformation after exposure to hot-fill conditions of 95 °C and 85 °C.
Keywords: co-polyesters; hot-fill; modified polyethylene terephthalate; multilayer packaging material; plastic recyclability; sustainability; transparency.