Assessment of Odor Removal in Rigid Polypropylene Waste: Comprehensive Characterization and Washing Comparison

Control of odor-active compounds in polymers is fundamental for both recycling and the circular economy. Among deodorization strategies for post-consumer plastics, washing plays a central role. This study focuses on the odor characterization of rigid polypropylene (PP) waste and the evaluation of different washing procedures for deodorization efficiency. Three washing regimes are tested, varying in temperature (25°C vs. 80°C) and medium (water vs. caustic soda with detergent). The resulting sample sets are classified as unwashed (UW), room temperature washed (RT), hot water washed (HW), and detergent washed (DW). Odor profiles are determined by descriptive sensory analysis, while odor-active compounds are identified using gas chromatography-olfactometry (GC-O). Ranking of odor contributions is performed through odor extract dilution analysis (OEDA). A total of 32 odorants are detected, of which 30 are identified via 2D gas chromatography-mass spectrometry/olfactometry (2D-GC-MS/O). Washed material exhibits flowery and soapy impressions, whereas unwashed PP is characterized by moldy notes. Hedonic ratings are lowest for UW, with statistically significant improvement observed in DW. Intensity ratings do not differ significantly across UW, RT, and DW, ranging from 7.5 to 5.5 on a 0-10 scale. These findings link chemo-sensory methods with odorant removal efficiency, advancing deodorization approaches for plastics.