Presentation and experimental verification of a physico-mathematical model describing the migration across functional barrier layers into foodstuffs.

For several years there has been an ongoing controversial scientific discussion about the so-called functional barrier concept which, although mostly connected with the re-use of recycled plastics for food packaging, has general relevance and is principally applicable to any type of multilayer structure. Concerning the definition of the efficiency of a functional barrier there exists different understandings, ranging from the absolute physical barrier requirement over the acceptance of toxicologically insignificant migration to a completely lag time-related definition. The starting point of this work was the fact that functional barriers are in most cases already in-situ-contaminated due to the thermally extreme coextrusion conditions of the manufacturing process. As a consequence, middle layer contaminants may already have penetrated the functional barrier of a food package and may provide direct contact with the foodstuff at the time when the package is filled. Nevertheless, depending on the individual food package parameters, the remaining functional barrier efficiency can still prevent inadmissible migration. To meet this real-life situation and to describe the underlying migration process a theoretical migration model was developed and experimentally verified in this work using artificially-contaminated multilayer HIPS sheets with different functional barrier thicknesses. An important result of this study was the finding that compared with the interdiffusion between the package's layers in situ during their formation in the coextrusion process, the interdiffusion at ambient temperature until the filling time point of the package is able to be neglected.