## 2 Results
### Migration, Weight Increase and Visual Changes of GPPS and HIPS with Food Simulants
#### 2.2.1 Migration Kinetics and Weight Increase Using the Food Simulant Isooctane  
The migration kinetics and weight increase of GPPS and HIPS into isooctane at 60 \({}^{\circ}\)C are reported in Figure 1.  
At this temperature, the relative migration values of the model substances and of styrene monomer and oligomers are very high and substantially similar for all the substances regardless of their molecular size, which reflects an extraction from the material rather than a diffusion-controlled migration process. After 10 days of contact it ranges from approx. 40 to 120% in case of GPPS and from approx. 40% to 80% in case of HIPS. The migration curves for all the investigated substances show a steady increase until the equilibrium is reached after approx. 20 days in case of GPPS and already after approx. 3 days in case of HIPS. The relative migration values higher than 100% in GPPS are most probably due to the analytical uncertainties of the extraction and migration values as well as to possible heterogeneity of the initial concentrations (see reported SD in Table 1). Styrene and the volatile test substances are completely transferred from the 350 \(\upmu\)m GPPS sheets into isooctane during the observation period. The gravimetric experiments show a significant weight increase of GPPS reaching 75% after 50 days. A slightly lower, but still clear increase was found on HIPS reaching 40% after 50 days. It is worth to be noted that at the testing conditions 60 \({}^{\circ}\)C for 10 days and 60 \({}^{\circ}\)C for 1 day using isooctane as food simulant, both investigated polymers are significantly swollen. This is demonstrated with a measured weight increase of 45% and 12% for GPPS and 30% and 21% for HIPS, respectively. Additionally, during the kinetic migration experiments in isooctane, visual changes of the GPPS and HIPS test specimens were monitored. The HIPS materials were deformed  
Figure 1: Migration kinetics and weight increase in isooctane at 60 \({}^{\circ}\)C: (**a**) Model substances and styrene from GPPS; (**b**) Styrene oligomers from GPPS. (**c**) Model substances and styrene from HIPS; (**d**) Styrene oligomers from HIPS. (rolled up) already after 4 h contact and become opaque and molded after 5 days; while the GPPS materials got softer and cloudy already after 2 h and became deformed (rolled up) after 8 days (see Supplementary material: Photos of visual changes). The migration kinetics and weight increase of GPPS and HIPS into isooctane at 40 \({}^{\circ}\)C are shown in Figure 2.  
At 40 \({}^{\circ}\)C the relative migration of the model substances and of styrene monomer and oligomers from GPPS in isooctane is drastically lower compared to 60 \({}^{\circ}\)C. After 50 days contact it ranges from 4% to 12% for the volatile substances (chlorobenzene and styrene), from 3% to 4% for the non-volatiles (phenyl cyclohexane, benzophenone, methyl stearate) and from 4% to 10% for the oligomers. The migration values are still increasing without approaching equilibrium. In case of HIPS, migration values in isooctane at 40 \({}^{\circ}\)C are similar or only slightly lower compared to the one obtained at 60 \({}^{\circ}\)C. The relative migration values range from 60% to 90% for the volatiles and 30% to 65% for the low volatiles (including the oligomers) after 10 days. The migration curves obtained for the volatile substances reach equilibrium already after approx. 1 day, while for the other compounds it takes approx. 14 days to reach the equilibrium. Interestingly, if compared with 60 \({}^{\circ}\)C, the weight increase measured for GPPS at 40 \({}^{\circ}\)C was drastically lower. It reached only 1% after 50 days and after 10 days 0.2%. Also in HIPS the measured weight increase was lower compared to 60 \({}^{\circ}\)C. It follows a steady increase, reaching up to 13% after 16 days and afterwards approached a plateau with 14% weight increase after 50 days.