Predicting migration of trace amounts of styrene in poly(styrene) below the glass transition temperature

The use of general purpose polystyrene (GPPS) as food packaging material is widespread. Therefore, the rate of migration of the styrene in GPPS is of interest in order to predict the potential exposure of consumers to styrene. Studies have shown a relatively weak dependence of the diffusion coefficient on the residual styrene content, and a strong dependence on temperature. We have compared the predictions of the free-volume theory with experimentally measured diffusivity data. The predictions and the measured values are observed to be consistent with each other. These results illustrate the capability of the free-volume theory of transport to predict the diffusivity of trace amounts of impurity in a glassy polymer.