Characterization of odors and volatile organic compounds changes to recycled high-density polyethylene through mechanical recycling

The application of post-consumer recycled (PCR) plastics is gaining growing attention, yet, the residual odor of recycled plastics hinders its application. In current study, electronic nose (E-nose), headspace-gas chromatog-raphy-ion mobility spectrometry (HS-GC-IMS), and headspace-gas chromatography-mass spectrometry (HS-GC-MS) combined with multiple chemometrics methods were analyzed to obtain different information of VOCs in rHDPE. In the meantime, the potential influence of the re-granulation process on VOCs was investigated. Relative odor activity values (ROAV) was applied to distinguish characteristic odors description of HDPE pellets in different manufacturers. Results showed that the established fingerprinting of VOCs based on HS-GC-IMS could provide an effective means for rapidly identifying rHDPE plastics. The more substantial amounts of VOCs in rHDPE flakes and pellets are terpenes and aliphatic hydrocarbons. Although the re-granulation process effectively removed most of the VOCs remaining in the washing process, acids, aromatic hydrocarbons, and terpenes were potentially residual in the rHDPE pellets. It was also revealed that terpenes and acids were the volatile odor compounds in most rHDPE pellets. Both d-limonene and octanal are the main key compounds of rHDPE pellets because of their maximum contribution to the overall odor, and together with other key odor compounds with similar odor, form the characteristic odor of citrus, sweet, and floral.