Fluorescence labeling of high density polyethylene for identification and separation of selected containers in plastics waste streams. Comparison of thermal and photochemical stability of different fluorescent tracers

Abstract

In recent years, a great effort has been devoted to the development of new automated identification and sorting methods for post-consumer plastics in the waste streams that reach the recycling processes, as the final properties of the recycled materials largely depend on the purity of the plastic residue. This work explores the use of fluorescence spectroscopy as a complementary technique to address the limitations of the current technologies. Specifically, the use of fluorescent markers for the removing, for technical or safety related issues, of selected high density polyethylene containers from the waste stream has been studied. The results indicate that identification by extrinsic fluorescence can be easily achieved even with small proportion of markers (10−3wt%) without significant change of the polymer structure. The effect of thermal, hygrothermal and photochemical degradation on the fluorescence emission has been analyzed. Although the signal intensity decreases during the accelerated degradation, distinguishable fluorescent emission was recorded even after sample exposure to aggressive conditions, thus enabling the correct identification of the marked plastics.