Figure 1: Evolution of the infrared peak area of C–H functional groups.

All of the experiments were performed at 30 keV and 300 K. This evolution is documented for (a) polyethylene (PE), (b) polystyrene (PS) and (c) polyethylene terephthalate (PET). For each sample, the intensity of the infrared signal related to CH₂ (1,465 cm⁻¹), CH (2,890 cm⁻¹) and ring (3,030 cm⁻¹) are considered. The peak areas (namely A_CH2, A_CH, A_ring) are normalized to the peak area of non-irradiated starting materials. On the three panels, the blue region represents the plateau, whereas structural, compositional and isotopic changes are still functions of the electron dose in the grey area. The doses required to reach 90% of the structural plateau delimit the blue and grey regions of the plots.