The semi chemical method upgrades post consumer PET to food contact grade rPET, with thermal stability and cleanliness similar to raw materials

Research Overview: A study published in Packaging Technology and Science proposed a semi chemical process (esterification condensation) for converting post consumer PET into food grade recycled PET (rPET). This method is different from conventional physical and chemical recycling routes: post consumer PET is copolymerized with monomers ethylene glycol (EG) and terephthalic acid (TPA), then undergoes esterification and condensation reactions, and finally rPET and its products are obtained through solid-state polymerization (SSP). The research objective is to achieve high-value recycling of waste plastics and provide a basis for the application of rPET in the field of food contact materials.

Changes in Structure and Thermal Properties

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 attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR).

. The results showed that during the esterification stage, a large amount of “cyclic polyester oligomers” were formed from oligomers, and this stage had the lowest thermal stability; With the advancement of subsequent pre polymerization and other processes, the molecular chain grows, the structure becomes denser, and the thermal stability is significantly improved. The rPET and its products obtained by solid-state condensation have smooth and dense surfaces, and their thermal stability, melting behavior, and chemical structure are highly consistent with those of native PET (vPET). ATR-FTIR analysis further confirmed that the process did not alter the basic chemical backbone of PET.

Food Contact Safety Assessment

To evaluate the safety of the final product as a food contact material, the study analyzed the types and concentration changes of volatile, semi volatile, and non-volatile organic compounds in rPET during semi chemical processes using 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 showed that after esterification and condensation reactions, the residual amounts and types of volatile, semi volatile, and non-volatile substances were effectively controlled. Only three volatile substances (styrene, nonanal, EG), one semi volatile substance (bis (2-hydroxyethyl) terephthalate), and one non-volatile substance (TPA-EG) 2 were detected in the final food contact grade rPET material. The study suggests that this recycling process significantly improves the safety of rPET, laying a theoretical foundation for its subsequent research and development in the field of food contact.

Significance for the polymer additive industry

From the perspective of packaging materials, this study provides a semi chemical upgrade route between physical recycling and complete chemical depolymerization, making post consumer PET close to raw materials in terms of structural density and thermal stability. This has reference value for improving the usable proportion of recycled materials in food contact packaging.

. For the processing stabilizer system, the low thermal stability exhibited by rPET during the esterification stage suggests that in actual extrusion, injection molding, and solid-state polymerization processes, the formulation design of antioxidants and processing stabilizers needs to pay attention to the degradation risk of recycled materials at different process stages to maintain molecular chain integrity and color stability. At the same time, this study provides a detection approach for the cleanliness evaluation of food contact recycled materials by systematically analyzing volatile, semi volatile, and non-volatile residues. It also suggests that additive companies need to consider migration risk control in the blending system of new and recycled materials. With the gradual maturity of food contact grade rPET technology, research on the compatibility of antioxidants, processing stabilizers, and recycled materials is expected to become an important direction in the field of packaging materials.

Information source:From Post‐Consumer to Food‐Contact Materials: A Semi‐Chemical Upcycling Process of PET， Organized by Herun Chemical.