From Post‐Consumer to Food‐Contact Materials: A Semi‐Chemical Upcycling Process of PET

The high‐value recycling of waste plastic is a key challenge in achieving a circular economy. This study introduces an innovative semi‐chemical process for producing recycled polyethylene terephthalate (rPET) materials by copolymerizing post‐consumer PET with monomers (ethylene glycol [EG] and terephthalic acid [TPA]) followed by esterification and polycondensation, thus opening a new avenue for the high‐value utilisation of rPET that is distinct from conventional physical and chemical recycling approaches. The microstructure and thermal properties of rPET during the semi‐chemical process were characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier‐transform infrared spectroscopy with attenuated total reflection (ATR‐FTIR). To evaluate the safety of the final product as a food contact material, the variations in the types and concentrations of volatile, semivolatile and nonvolatile organic compounds in rPET during the semi‐chemical process were analysed via headspace gas chromatography–mass spectrometry (HS‐GC–MS), gas chromatography‐quadrupole tandem time‐of‐flight mass spectrometry (GC‐QTOF/MS) and ultra‐high performance liquid chromatography‐quadrupole time‐of‐flight mass spectrometry (UHPLC‐QTOF/MS). The results indicate that the esterification stage, characterised by the formation of numerous ‘cyclic polyester oligomers’ from oligomers, exhibited the lowest thermal stability. With the progression of subsequent processes (e.g., precondensation), molecular chains grow, resulting in a denser structure and a significant improvement in thermal stability. Ultimately, the rPET and its product obtained via solid‐state polycondensation (SSP) possessed a smooth and dense surface, with its thermal stability, melting behaviour and chemical structure being highly consistent with those of virgin PET (vPET). ATR‐FTIR analysis further confirmed that the process did not alter the fundamental chemical backbone of PET. Following treatment with esterification and polycondensation reactions, both the residual amounts and the number of species of volatile, semivolatile and nonvolatile substances were effectively controlled. The resulting food‐contact rPET material contained only three volatile substances (ethenylbenzene, nonanal, EG), one semivolatile substance (bis(2‐hydroxyethyl) terephthalate) and one nonvolatile substance (line (TPA‐EG) 2 ). This recycling process significantly enhances the safety of rPET, laying a theoretical foundation for its subsequent research and development in food‐contact related fields.