Diffusion of homologous model migrants in rubbery polystyrene: molar mass dependence and activation energy of diffusion

Abstract

Published diffusion prediction models for the diffusion of additives in food packaging simplify reality by having a small number of parameters only. Therefore, extrapolation of such models to barrier polymers, larger ranges of temperature and/or additive molecular weight (M_W ) is questionable. Extra data is still required to generalize these existing prediction models. In this paper, diffusion of a specifically designed homologous set of model additives (from 236 to 1120 g mol⁻¹) was monitored in two polystyrenes in the rubbery state (from 100 to 180°C): syndiotactic semi-crystalline polystyrene and its amorphous equivalent. Variations in associated diffusion coefficient D and activation energy Ea with migrant M_W and temperature were surprisingly low. Comparison of experimental behaviour with model predictions was performed. In their actual form, none of the models is capable of describing all experimental data, but there is evidence of convergence of the different approaches.

Keywords:

• chromatographic analysis
• packaging overall migration
• packaging plasticizers
• plasticizers
• simulants