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

Frank Welle

doi:10.3390/polym13081317

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 EA and the pre-exponential factor D0 were determined. As expected, the activation energies of diffusion EA 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 EA and D0, prediction parameters for diffusion coefficients were established.

Highlights

Polystyrene (PS) is widely used as packaging materials for food [1]
Diffusion coefficients were determined from desorption kinetics into the gas phase using spiked General Purpose Polystyrene (GPPS) and high impact polystyrene (HIPS) sheets as well as from permeation kinetics through a thin GPPS film
Diffusion coefficients DP of several organic compounds were determined by use of two independent methods: (i) Desorption kinetics from spiked GPPS and HIPS sheets and (ii) permeation kinetics on a thin (34 ± 1 μm) non-spiked GPPS film

Summary

Introduction

Crystal polystyrene (general purpose polystyrene (GPPS)) is used for containers for a variety of foods and as disposable cups for beverages. Opaque HIPS is used for food containers and yogurt cups. GPPS and HIPS plastics have poor barrier properties to permanent gases like oxygen and carbon dioxide. This reduces the shelf life of food packed in PS, but on the other hand, makes HIPS a good packaging material for yogurt and milk products as some penetration of oxygen is necessary to assist the yogurt fermentation process. Foamed PS is thermoformed into a variety of trays for meat, poultry, fish, fruit and vegetables as well as containers for eggs, and fast foods, and disposable cups for hot beverages. PS is used for technical products or applications such as electronics, furniture, toys, building insulation and automotive parts

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