RAMAN SPECTROSCOPY FOR SENSING AND SORTING WEEE

In PLAST2bCLEANED, Raman spectroscopy is applied for the pre-processing step of the recycling process, in order to improve the current sorting process of Waste Electric and Electronic Equipment (WEEE) plastics.

Raman spectroscopy is an analytical technique based on light scattering that uses a laser as a source of high intense monochromatic light. Different laser wavelengths ranging from ultraviolet (UV) to near-infrared (NIR) can be employed. The sample is irradiated with the laser beam and scattered radiation of different wavelengths is produced. The scattered light is detected in the spectrometer, which transforms the signal into a spectrum.

The Raman spectrum is a chemical fingerprint of a compound that gives information about its molecular structure. Consequently, Raman spectroscopy is a useful technique for chemical identification, being complementary to other spectroscopic techniques used for plastics sorting in recycling plants, such as NIR spectroscopy.

In order to maximise the Raman signal and to reduce the fluorescence effect, several parameters are evaluated for polymers identification: laser power, integration time, or the use of different laser wavelengths in the NIR range.

PLAST2bCLEANED aims to develop a mechanical sorting process based on Raman spectroscopy, that will lead to identifying several polymers in any colour which contain different additives like brominated flame retardants (BFR) or pigments, in order to separate High Impact Polystyrene (HIPS) and Acrylonitrile Butadiene Styrene (ABS) fractions from WEEE streams. These sorted polymers will be further purified for their reuse in other applications.

Raman equipment used in the PLAST2bCLEANED project.
Laser incident on a sample
Raman spectrum of a WEEE sample

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