## 2 Results
### Migration, Weight Increase and Visual Changes of GPPS and HIPS with Food Simulants
#### 2.2.3 Migration Kinetics and Weight Increase Using the Food Simulant 50% Ethanol  
The migration kinetics and the weight increase of GPPS and HIPS into 50% ethanol at 60 \({}^{\circ}\)C are shown in Figure 7. Relative migration of styrene oligomers for both polymers in 50% ethanol at 60 \({}^{\circ}\)C was below 1% up to 50 days contact (data not shown).  
The migration of the target volatile compounds increased over time. After 10 days of contact, migration of volatiles from GPPS reached 13% (styrene) or 27% (toluene and chlorobenzene) and from HIPS 20%. In case of low volatiles compounds migration remained in the range of the detection limits. As regard the weight increase related to 50% ethanol at 60 \({}^{\circ}\)C, after 10 days migration contact, a weight increase of 1.2% for GPPS and 1.3% for HIPS was measured. For GPPS it remained constant until the last observed time point (127 days, data not shown), while for HIPS it increased after 50 days approaching plateau at 10% after 200 days (data not shown). No visual changes were observed for GPPS while for HIPS they were appreciable. Already after 5 days contact the HIPS sample materials became cloudy; and after 16 days the color changed to yellow. (see Supplementary material: Photos of visual changes).  
The migration kinetics of target substances from GPPS and HIPS in 50% ethanol at 40 \({}^{\circ}\)C are shown in Figure 8. Migration of oligomers was not detectable.  
The migration extent from GPPS was lower than from HIPS. After 10 days, migration of styrene from GPPS was not detectable, the relative migration of toluene reaches 4%, while in case of HIPS the relative migration of the volatiles was approx. 10%. In case of low volatiles compounds migration remained in the range of the detection limits. Migration of styrene from GPPS was detectable only after 20 days and increased reaching 5% only after 50 days whereas at the same condition it reached 15% in case of HIPS. After 10 days migration contact in 50% ethanol at 40 \({}^{\circ}\)C a weight increase corresponding to 1.1% for GPPS and 1.3% for HIPS was observed. The weight increase remained constant until the end of the kinetic experiments with 127 days and 159 days for GPPS and HIPS respectively. No visual changes were appreciable using 50% ethanol at 40 \({}^{\circ}\)C until 44 days for GPPS, when the samples became slightly cloudy. In case of HIPS, the first visual changes were observed after 64 days, when the samples became slightly yellow.  
The migration kinetics from HIPS in 50% ethanol at 20 \({}^{\circ}\)C are shown in Figure 9. Relative migration of styrene oligomers from HIPS in 50% ethanol at 20 \({}^{\circ}\)C was below 0.5% until 157 days (data not shown). Migration from GPPS was below the analytical detection limits.  
Figure 7: Migration kinetics and weight increase in 50% ethanol at 60 \({}^{\circ}\)C: (**a**) Model substances and styrene from GPPS; (**b**) Model substances and styrene from HIPS. Note: Due to analytical interferences, migration of methyl stearate from GPPS and HIPS in HIPS in 50% ethanol at 60 \({}^{\circ}\)C can not be measured.  
The relative migration of styrene and the other volatiles was approx. 2-2.5% after 10 days. In case of low volatiles compounds migration remained in the range of the quantification limits. The maximum weight increase was 1.1% reached after 44 days both for GPPS and HIPS. It is to worth to be noted that at the testing condition 20 \({}^{\circ}\)C for 10 days using 50% ethanol as food simulant, the GPPS and HIPS polymer are only slightly swollen (0.7 and 0.9% respectively). No visual changes of the test specimens were observed until the last kinetic time point.