Transfer of contaminant during the processing of thick bi-layer food packages made of recycled and virgin polymer layers

A new route of recycling old polymers consists of using them as new food packages. Because of the potential contamination of the old polymer resulting from its previous use, the new packages are made of the old polymer layer bound to a virgin polymer layer. As it takes some time for the contaminant to diffuse through the bi-layer packaging, the food is protected over a period of time. The process of binding the two polymer layers is studied, when the two layers are heated at around the melted temperature and then cooled down at room temperature. Heat transfer by conduction through the polymer and the mould during the heating stage is considered as well as the cooling period in air. During this heating and cooling period, the process of contaminant diffusion through the two polymer layers is evaluated by considering a temperature-dependent diffusivity. The results are expressed in terms of profiles of temperature and of profiles of concentration of contaminant developed through the polymer layers. The kinetics of contaminant transfer from the recycled layer to the virgin polymer layer are also determined, for various thicknesses of the package. Dimensionless numbers are used, as well as various thicknesses of the package.