Migration of styrene from polystyrene foam food-contact articles

Polystyrene foam is used in many food-contact articles such as plates, cups, bowls, egg cartons, meat trays and hinged ‘carryout’ containers. In most of these applications the food is in contact with the article for a relatively short period of time at mild temperatures (up to 130°F), or for longer periods of time at refrigerated temperatures (40°F). The extent of migration of residual styrene from foam articles under these conditions is of interest in order to predict potential exposure of consumers to styrene from food-contact polymers. Studies of styrene migration from all polystyrene foam articles except egg cartons were completed using food oil as the simulant. Results showed that the amount of styrene migrating from the various food-contact articles made with thermoformed polystyrene sheet into food oil was proportional to the square root of time of exposure. The mean diffusion coefficients derived from these data, assuming the migration was Fickian in nature, showed a linear relationship between the log of the diffusion coefficient and the inverse of the absolute temperature of exposure from 70 to 150°F (21–66°C). The mean diffusion coefficients ranged from about 4.5E-11 cm2/s at 70°F to 3.4E-9 cm2/s at 150°F. Among the four thermoformed articles exposed to food oil, the diffusion coefficients varied by a factor of four or less at a given temperature. The migration of styrene from egg cartons was examined using conditions simulating ‘typical’ exposure temperature and time with 8% ethanol as the simulant (31 days at 40°F (4°C)). No migration of styrene was observed under this condition, with a detection limit of <0.01μg/cm2.