Elaboration and Characterization of Traced Polypropylene with Rare Earth Oxides for Automatic Identification and Sorting of End-of-Life Plastics

The rare earth oxides can be used as tracers for the identification of polymer materials. This study focused on the detection of these particles and their effects on the mechanical and thermal properties of polypropylene (PP). A new method was carried out to increase the sorting selectivity of PP during end of life recycling process and to improve the efficiency of sorting and its high speed identification. The tests were realized in a test system device which allows the collection of static measurements of the samples spectrum through the use of energy dispersive X-ray fluorescence technology. Five of the seven tracers tested are clearly visible and distinguishable from the background sample by their K-alpha 1 energy line at concentration levels of 0.1 and 0.145 wt%. For the two remaining tracers, their K-alpha 1 energy lines come out at the same domain of energy as the source. Dispersion of rare earth oxides at 0.1 and 1 wt% do not have a significant impact on the crystallization and melting temperature as well as on the temperature of maximum decomposition rate. The addition of 1 wt% of rare earth oxides leads to a slight increase of the flexural modulus, whereas the addition of 0.1 and 1 wt% causes a decrease of the elongation at break. SEM images show a homogenous dispersion of tracers in the PP matrix.