Behavior and removal of semi-volatile organic compounds during PET mechanical recycling processes

Recycling post-consumer polyethylene terephthalate (PET) for reuse in food contact materials is a current trend in green development. Achieving effective removal of contaminants during the recycling process is crucial for ensuring the quality of recycled PET (rPET). This study utilized gas chromatography coupled with quadrupole time-of-flight mass spectrometry (GC-QTOF-MS) to comprehensively characterize the presence and removal efficiency of semi-volatile organic compounds (SVOCs) in rPET derived from four main recycling stages, including cold-water washing (C-rPET), preliminary decontamination (P-rPET), melt-extrusion step (M-rPET), and the solid state polycondensation step (S-rPET). The results showed that 110, 106, 79, and 70 compounds were tentatively identified in C-rPET, P-rPET, M-rPET, and S-rPET, respectively, and melt-extrusion was the main decontamination stage. To further evaluate the removal efficiency of the recycling process, five surrogates (cyclohexylbenzene, methyl salicylate, methyl stearate, benzophenone, bis(2-ethylhexyl) terephthalate) were selected for the challenge test, and a quantitative method combined accelerated solvent extraction (ASE) with GC-MS/MS was established. The results demonstrate that the recovery process is highly efficient as it effectively removes 97.8 % of bis(2-ethylhexyl) terephthalate and more than 99.5 % of other surrogates. Hierarchical cluster analysis (HCA) was utilized to group compounds according to their intensity distribution during the recovery process to investigate the behavior and fate of detected compounds. Four representative trends were defined along with the corresponding compounds. The above research is helpful for the improvement of recycling processes and provides a complete technical system for the conduct of rPET challenge tests in China.