Characterization of Odorous Compounds in Recycled Materials

Significance of the Topic

Modern waste management emphasizes recycling polymer materials, yet residual odorous compounds can impair product performance and consumer acceptance. Reliable detection and characterization are thus critical for quality control, regulatory compliance, and ensuring material reuse within circular economy frameworks.

Objectives and Study Overview

This study aims to develop and compare sampling and analytical strategies for identifying odorous volatile organic compounds in recycled plastics, focusing on method sensitivity, practical sampling conditions, and comprehensive odor profiling.

Methodology

• Sample Collection and Preparation
  
  • Tedlar bag sampling custom bags with Tenax sorbent, controlled temperature (up to 80°C) for headspace collection
  • Centri® automated platform thermal desorption, headspace trapping, HiSorb sorptive extraction
• Analytical Techniques
  
  • TD-GC-MS with olfactometry using trained panelists for real-time odor detection
  • GCxGC-HRTOFMS and flame ionization detection for high-resolution two-dimensional separation and accurate mass analysis

Instrumentation Used

• Thermal desorber coupled to GC-MS and GCxGC-HRTOFMS systems
• High-resolution time-of-flight mass spectrometer resolving power greater than 25 000, mass accuracy below 1 ppm
• Flame ionization detector for complementary response
• Continuous online sniffing interface in a purified-air sensory room

Main Results and Discussion

• Sampling Efficiency
  
  • HiSorb extraction detected eight odorous compounds (intensity up to 1.5, equivalent to 1 g sample) versus 29 compounds (intensity up to 2.0, equivalent to 30 g sample) for Tedlar bag sampling
  • Headspace trap optimization (1 hour at 120°C) improved odor detection in polypropylene and recycled polypropylene, achieving 34 odors versus 46 with the Tedlar bag method under different sampling mass conditions
• Complex Sample Analysis
  
  • GCxGC-HRTOFMS/FID resolved thousands of peaks (3 186 HRMS peaks vs 799 FID peaks) revealing matrix interferences and trace odorous species
  • Targeted extracted ion chromatograms for carbonyl species (m/z 43.0178), pyrazines, nitrogen and sulfur containing compounds identified key odorants such as diketones and thiophene derivatives
  • Comparison of reference and processed samples showed elimination of roasted and fatty odor notes after recycling processes

Benefits and Practical Applications

• Enhanced sensitivity in odor detection enables analysis of lower sample masses and shorter collection times
• Combined olfactometry and high-resolution mass analysis guides targeted deodorization and quality control strategies
• Methodology supports process monitoring in polymer recycling facilities to ensure regulatory compliance and product consistency

Future Trends and Potential Applications

• Integration of real-time olfactometry with advanced data analytics and machine learning
• Development of online monitoring platforms for continuous VOC surveillance in industrial settings
• Expansion of portable GCxGC and high-resolution mass spectrometry for in-field odor diagnostics

Conclusion

Comprehensive sampling and analytical workflows combining olfactometry and high-resolution GCxGC-HRTOFMS/FID effectively characterize odorous volatile compounds in recycled plastics. This approach enhances sensitivity, informs process optimization, and underpins quality assurance in sustainable material reuse.