Diffusion Coefficients and Activation Energies of Diffusion of Organic Molecules in Polystyrene below and above Glass Transition Temperature

Frank Welle

doi:10.3390/polym13081317

Diffusion Coefficients and Activation Energies of Diffusion of Organic Molecules in Polystyrene below and above Glass Transition Temperature

Polymers (Basel). 2021 Apr 16;13(8):1317. doi: 10.3390/polym13081317.

Author

Frank Welle¹

Affiliation

¹ Fraunhofer Institute for Process Engineering and Packaging (IVV) Giggenhauser Straße 35, 85354 Freising, Germany.

Abstract

General Purpose Polystyrene (GPPS) and High Impact Polystyrene (HIPS) is used in packaging food as well as for technical products. Knowledge of the diffusion behavior of organic molecules in polystyrene (PS) is important for the evaluation of the diffusion and migration process. Within this study, diffusion coefficients were determined in GPPS and HIPS below and above the glass transition temperature. Diffusion coefficients were determined from desorption kinetics into the gas phase using spiked GPPS and HIPS sheets as well as from permeation kinetics through a thin GPPS film. Overall, 187 diffusion coefficients were determined in GPPS and HIPS at temperatures between 0 °C and 115 °C. From the temperature dependency of the diffusion coefficients 45 activation energies of diffusion E_A and the pre-exponential factor D₀ were determined. As expected, the activation energies of diffusion E_A show a strong dependency from the molecular volume of the investigated substances. At the glass transition temperature, only a slight change of the diffusion behavior were observed. Based on E_A and D₀, prediction parameters for diffusion coefficients were established.

Keywords: activation energy; diffusion coefficients; diffusion modelling; functional barrier; polystyrene.