Migration testing of polyethylene terephthalate: Comparison of regulated test conditions with migration into real food at the end of shelf life
Polyethylene terephthalate (PET) in contact with food must comply with the requirements laid down in the European Regulation (EU) 10/2011, which specifies conditions for migration tests. For real contact times longer than 30 days, accelerated migration tests are performed at elevated temperatures for a maximum of 10 days at 60°C. These conditions should represent the end of the shelf life (e.g. 365 days at 23°C) and are calculated using the Arrhenius equation on the basis of a default activation energy of 80 kJ/mol. However, for PET, it is well known that the activation energy is strongly dependent on the molecular size of the migrant. Small molecules like acetaldehyde have activation energies in PET of ~80 kJ/mol. For larger molecules like 2-aminobenzamide with a predicted activation energy of diffusion of 134.4 kJ/mol, the storage times at 60°C and 40°C equivalent to the migration after 1 year at 23°C are 0.85 and 18.9 days, respectively. These findings were confirmed by experimental migration tests. For 2-aminobenzamide, migration for 10 days at 60°C corresponded to a storage time at 23°C of 11.7 years, which is significantly higher than the long-term storage of more than 6 months as foreseen in Regulation (EU) 10/2011. For larger molecules, the corresponding storage times at 23°C would even be longer, thus overestimating by far the migration at the end of shelf life. Contact conditions of 10 days at 60°C are too severe for PET. Migrant-specific and polymer-specific diffusion parameters should therefore be considered when designing accelerated migration tests for long-term applications.