Contaminants and their Levels of Retention in Extruded, Recycled Poly(Ethylene Terephthalate) from Curbside Collection. Part 1: Extraction Kinetics and Particle Size Effects

Abstract

In the first phase of our studies of the contaminants and their levels in curbside-collected poly(ethylene terephthalate) (PET) subjected to a recycling process, we analysed the washed and dried, shredded PET (flake). Of the semi-volatile contaminants found, 26 were below the US FDA threshold of 215 ppb and six were above. Additionally, it was found that surface levels of contaminants far exceeded average concentrations in the bulk of the flake, raising questions about the appropriateness of sampling procedures. In this second phase (again using dichloromethane Soxhlet extractions for the most part), we examined contaminant levels after the flake was subjected to vacuum extrusion, to complete the recycling process. Initially amorphous, extruded pellets were annealed to introduce crystallinity and allow grinding, in order to examine the effect of particle size. Much reduced concentrations of contaminants were found (all <215ppb). There were no significant differences in contaminant levels as a function of particle size, thus indicating a uniform distribution throughout the extruded material and no need for particle size reduction before sampling and analysis. However, whilst 3 h was sufficient to obtain quantitative extractions from the ground, annealed particles in each size range (0-300 μm, >300-425 μm and >425-700 μm), approximately 8 h were required for the unground annealed pellets.