Detection Methods of Polyethylene Impurities in Food-grade Recycled PET

LI Huiyong; LIN Qiaoxin; CAO Liming; YU Changyun; HUANG Guangchi; XIONG Xiaoting; LI Lu; LI Zerong; HE Guoshan

doi:10.19554/j.cnki.1001-3563.2026.17.003

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Packaging Engineering ›› 2026, Vol. 47 ›› Issue (17) : 18-25. DOI: 10.19554/j.cnki.1001-3563.2026.17.003

Special Topic on Sustainable Design and Systemic Transformation of Plastic Packaging for Liquid Foods

Detection Methods of Polyethylene Impurities in Food-grade Recycled PET

LI Huiyong¹, LIN Qiaoxin², CAO Liming^2,*, YU Changyun³, HUANG Guangchi¹, XIONG Xiaoting¹, LI Lu¹, LI Zerong¹, HE Guoshan^1,*

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Abstract

The work aims to establish a detection strategy based on Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), and Thermogravimetric Analysis (TGA) and systematically compare the ability of the three techniques to identify trace amounts of polyethylene (PE) impurities in recycled polyethylene terephthalate (rPET), providing methodological support for the development of relevant testing standards. Pure PET and PE were used as raw materials, and simulated blended samples with PE mass fractions of 1%, 2%, 3%, and 5% were prepared via the masterbatch dilution method by a twin-screw extruder. The three methods described above were employed to characterize the blended samples, and two actual rPET samples were selected to validate the applicability of the methods. DSC could detect PE impurities with a mass fraction of ≥1%, but PE impurities at lower contents required further study. FTIR, based on the characteristic methylene C—H bending peak at 1 472 cm^-1, exhibited higher sensitivity for impurity identification and was suitable for detecting trace impurities. TGA showed limited detection sensitivity due to the considerable overlap between the decomposition temperature ranges of PET and PE, but the DTG peak shape could serve as an auxiliary basis for judgment. Analysis of actual rPET samples indicated that FTIR could effectively detect PE impurities in the samples, whereas DSC and TGA could provide supplementary criteria for judgment. DSC is suitable for rapid preliminary screening of PE impurities in rPET, FTIR is more reliable for identifying trace PE impurities, and TGA can serve as an auxiliary cross-validation tool. The three methods are complementary in principle, and their combined use can improve identification accuracy, providing technical support for the establishment of standard methods for detecting PE impurities in food-grade rPET.

Key words

recycled PET / polyethylene impurities / infrared spectroscopy (FTIR) / differential scanning calorimetry (DSC) / thermogravimetric analysis (TGA)

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LI Huiyong, LIN Qiaoxin, CAO Liming, YU Changyun, HUANG Guangchi, XIONG Xiaoting, LI Lu, LI Zerong, HE Guoshan. Detection Methods of Polyethylene Impurities in Food-grade Recycled PET[J]. Packaging Engineering. 2026, 47(17): 18-25 https://doi.org/10.19554/j.cnki.1001-3563.2026.17.003

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