## 3 Discussion  
There is a need to maintain scientific approaches to evaluate the safety of polymers that are intended to be in contact with food beyond historically established experimental testing, which is time consuming and expensive. On the other hand, it is indispensable to maintain regulation approaches that are in line with recent scientific developments. Current regulation approaches are necessarily conservative but are not always reflective of real-life situations. This is the specific case for repeated-use food contact applications, in which contact time is predominantly short and service life is predominantly long compared to single-use applications. Figure 11: Migration map for PP for contact times of 6 h (**a**) and 1 day (**b**). Molecular weight in g/mol against temperature (T) in \({}^{\circ}\)C. Deviation of migration in mg/dm\({}^{2}\) independent of partition coefficient (K\({}_{\text{P,F}}\)) expressed in % at a given initial concentration (1000 mg/kg), material thickness (2000 \(\upmu\)m), and area to volume ration (6 dm\({}^{2}\) per kg food). Figure 10: Migration map for PA6 for contact times of 1 day (**a**) and 10 days (**b**). Molecular weight in g/mol against temperature (T) in \({}^{\circ}\)C. Deviation of migration in mg/dm\({}^{2}\) independent of partition coefficient (K\({}_{\text{P,F}}\)) expressed in % at a given initial concentration (1000 mg/kg), material thickness (2000 \(\upmu\)m), and area to volume ratio (6 dm\({}^{2}\) per kg food). Figure 9: Migration map for ABS for contact times of 1 day (**a**) and 10 days (**b**). Molecular weight in g/mol against temperature (T) in \({}^{\circ}\)C. Deviation of migration in mg/dm\({}^{2}\) independent of partition coefficient (K\({}_{\text{P,F}}\)) expressed in % at a given initial concentration (1000 mg/kg), material thickness (2000 \(\upmu\)m), and area to volume ratio (6 dm\({}^{2}\) per kg food). Using modern science to evaluate the safety of repeated-use food contact polymers will provide opportunities to better evaluate and enforce the safety of polymers, and this will help to support the validation of compliance and build confidence with stakeholders. A lot of developments have taken place that improve our understanding of how to better predict the safety of polymers. The solution to the diffusion law provides the possibility to predict the migration of individual substances that are present in the food that is contact with plastic, allowing polymers to be evaluated as being safe to use for single- and repeated-use applications, provided that the related mass transfer parameters for diffusion and the partition coefficient are accessible. Meanwhile, several generally applicable estimation procedures to determine the diffusion coefficients of the migrants in polymers exist were validated by a significant number of experimental values [9; 10; 13], but no generally applicable and simple estimation procedure to determine the partition coefficients between the plastic food contact layer and food are available. Under these circumstances, it is of particular interest to determine under which circumstances knowledge of the related partition coefficient is of minor importance. This study determined that the impact of the partition coefficient between the plastic food contact layer and food on migration from the plastic to food might be negligible under certain conditions, i.e., the impact of the partition coefficient on the migrating amount is less than 10%. This is the case for low diffusivity polymers such as styrene-based polymers (PS, ABS, SAN, etc.) or polyesters (PET, etc.)