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

## TL;DR

This study evaluates how washing affects odors in used polypropylene plastics, finding that detergent-based washing improves smell and could help recycling efforts.

## Contribution

The study links sensory and chemical analysis to show how washing conditions affect odor removal in polypropylene waste.

## Key findings

- Detergent washing significantly improves hedonic ratings compared to unwashed polypropylene.
- Hot water and detergent washing reduce moldy odors and introduce soapy and flowery notes.
- 30 odor-causing compounds were identified using advanced analytical methods.

## Abstract

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.

This study examines how washing modifies odors in post‐consumer polypropylene plastics. Different washing conditions are compared by using sensory panels and advanced chemical analysis. Hot and detergent‐based washing removes key odor‐causing compounds, replacing moldy notes with cleaner, soapy impressions. The results show how targeted washing steps may enhance recycling potential and plastics circularity.