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

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.

Recycling of Post-Consumer Packaging Materials into New Food Packaging Applications—Critical Review of the European Approach and Future Perspectives

“…These factors are not changed here, because it is not known which over-estimation factors EFSA will assume for HIPS. Most probably, the over-estimation factor of the A P parameters for PS will be more like PET than HDPE, or even higher, as can be expected from a recent publication of realistic and not worst-case diffusion coefficients for HIPS [42]. As a low diffusive polymer, the minimum required cleaning efficiencies are in a similar range as found for PET.…”

“…The migration prediction model used by EFSA constitutes another conserv is well-known that the underlying AP model for the prediction of the diffusion co in PET highly over-estimates the migration, especially for larger molecules [47]. alistic prediction models have been developed and are published in the scientific l for PET [48] and PS [42]. These more realistic prediction models for diffusion co in PET and PS are based on experimentally determined activation energies of dif the polymers.…”

“…More realistic prediction models are also available for GPPS and HIPS [42], and they will change the minimum cleaning efficiency for recyclate applications as discussed in Section 6.3, in a similar manner compared to the much more over-estimative A P prediction model. Unfortunately, more realistic prediction models are not available for polyolefins, which means that the safety evaluation of polyolefin recycling still processes the A P prediction model that needs to be applied.…”

Impact of Partitioning in Short-Term Food Contact Applications Focused on Polymers in Support of Migration Modelling and Exposure Risk Assessment

“…For the typical polymers and migrants that are used in food contact applications at ambient temperatures, the diffusion coefficient ranges between 10 −10 cm 2 /s (high diffusivity polymer, small molecule) and 10 −15 cm 2 /s (low diffusivity polymer, huge molecule). Figure 3 shows examples for polypropylene (PP) [ 21 ], general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS) [ 22 ], acrylonitrile butadiene styrene copolymer (ABS) [ 21 ], styrene acrylonitrile copolymer (SAN [ 21 ]), and polyethylene terephthalate (PET) [ 10 ].…”

Migration Testing of GPPS and HIPS Polymers: Swelling Effect Caused by Food Simulants Compared to Real Foods

“…Migration testing employing aqueous food simulants lead to under-estimation of the migration processes occurring in real food products [26][27][28][29][30]. On the other hand, it has been recognized that certain food simulating liquids like ethanol/water mixtures, n-heptane or isooctane strongly interact with styrene based materials leading to an overestimation of the migration which results into too high diffusion coefficients due to swelling and stress cracks [27,31,32].…”