Table 1 Identification criteria and necessary peaks for polymer classification by domain experts

PE

1052, 1120, 1295, 1440

If three peaks are unique, one can be shifted. If four peaks match, they do not require the highest intensity. Two out of four peaks can be wider if the position is correct. The peak at 1440 cm⁻¹ can be "smeared" and shifted.

PET

1100, 1278, 1620, 1735

The peaks at 1735 cm⁻¹ (which are "hilly" in parts) and 1620 cm⁻¹ (prominent) are necessary for identification. The peaks at 1100 cm⁻¹ and 1278 cm⁻¹ may not be present where there is a low signal-to-noise ratio.

PP

785, 820, 1145, 1328, 1458

The peaks at 785 and 820 are necessary for identification. The peak at 785 is usually higher than the peak at 820 cm ⁻¹. A slight shift of the peaks is possible. The peaks at 1145 cm⁻¹ and 1328 cm⁻¹ may not be present where there is a low signal-to-noise ratio.

PS

990, 1020, 1328, 1607

The peaks at 990 cm⁻¹ and 1020 cm⁻¹ are necessary for identification. The peak at 1020 cm⁻¹ is only marginally visible where there is a low signal-to-noise ratio. In this case, the other peaks are necessary for identification.

PVC

612, 663, 1435

The peaks at 612 cm⁻¹ and 663 cm⁻¹ are necessary for identification. The peak at 612 cm⁻¹ is usually higher. Both peaks are broad and they converge.