Application of shifted excitation Raman difference spectroscopy for material identification towards sustainable recycling processes

Abstract:
The ability to rapidly identify different plastic and textile materials is crucial on the way towards efficient recycling pathways. Raman spectroscopy is a well-established analytical method that provides substance-specific information, but laser-induced fluorescence and strong absorption in case of carbon black colored materials are main obstacles. Shifted excitation Raman difference spectroscopy (SERDS) is a physical approach using two slightly shifted laser wavelengths to overcome these challenges. Using an in-house developed 785 nm one-chip dual-wavelength diode laser as excitation light source, pilot SERDS laboratory investigations are exemplarily conducted on 21 dyed and undyed textile samples and 8 black plastic specimens. We selected an excitation spot size of approximately 100 µm diameter and optical output powers < 30 mW at the sample. SERDS can effectively separate material-specific target Raman signals from background interferences and thus enables rapid material identification of textiles and plastics with measurement times on the order of seconds. These results demonstrate the potential of SERDS as a promising inspection tool for the recycling industry.