Remote Raman detection of seven groups of plastics

At present, only two groups of plastic, polyethylene (PET) and high-density polyethylene (HDPE) among seven plastic groups are widely and easily recycled. However, the majority of plastic wastes are diverted to landfills due to insufficient identification. Therefore, there is a need for remote sensing techniques with rapid and non-contact identification for plastics without requiring physical handling to increase sorting efficiency in future industrial applications for recycling. This study demonstrates the detection of seven common plastic groups using a remote Raman system utilizing a 532 nm frequency doubled Nd:YAG pulsed laser for excitation. Remote detection of plastics is accomplished at 10 m distance with 1 s integration time. Clear Raman peaks over the fluorescence background were observed with good spectral resolution. In addition, color of the plastic samples did not affect the Raman detection suggesting Raman measurements are insensitive to coloring chemicals which are usually present in low concentration. This allowed dependable differentiation among the polymer groups based on their molecular vibrational signatures. The results in this study suggest that remote Raman spectroscopy is an ideal technique that can provide rapid detection with very high confidence for chemical specificity that is required for reliable identification and sorting of diverse plastic types.