Plastic identification based on molecular and elemental information from laser induced breakdown spectra: a comparison of plasma conditions in view of efficient sorting

This work is dedicated to a comparison of plasma conditions for the accurate determination of some elements: Br, Cl, Ca, P and Sb, in polymers. The comparison of the plasma conditions to sort plastics according to CN, C2 and element signals was also investigated. The comparison of a helium atmosphere and an air atmosphere led to improved results using helium as a buffer gas. The improvement is obtained in two areas, it increased the detection of halogens (Br, Cl) usually employed as flame retardants. It was also found to significantly improve the discrimination based on simple calculations of C2/He and CN/He ratios. Best conditions were based on a laser emitting at 266 nm, with a low 6 mJ energy focalized on a 50 μm spot and the helium buffer gas. A plot of C2/He against CN/He was efficient to identify the four groups of plastics employed in this study: polystyrene, polypropylene, acrylonitryle-butadiene-styrene and acrylonitryle-butadiene-styrene/polycarbonate.