Characterization of the Composition and Thermal Decomposition Profile of Recycled Carpet Samples by TGA-FT-IR, TGA-MS, and TGA-GC-MS

Importance of the Topic

The accumulation of carpet waste, predominantly non-biodegradable nylon, presents environmental and landfill challenges. Efficient recovery of nylon from recycled carpets requires precise characterization of their composition and thermal behavior. Thermogravimetric analysis coupled with evolved gas analysis (TGA-EGA) offers a rapid, simultaneous assessment of mass loss and gaseous products, aiding recycling processes.

Objectives and Study Overview

This study aimed to evaluate TGA-FT-IR, TGA-MS, and TGA-GC-MS techniques for analyzing recycled carpet samples. Key goals included determining polymer types (Nylon-6 and Nylon-6,6), identifying decomposition products, and comparing the analytical capabilities of each coupling method.

Methodology

Samples were heated from 25 to 600 °C at 10 K/min under nitrogen (for TGA-FT-IR and TGA-MS) or helium (for TGA-GC-MS). Evolved gases were transferred through heated lines (220 °C for FT-IR/MS, 300 °C for GC-MS). In GC-MS measurements, gas was sampled every four minutes and separated on an Agilent HP-5MS column at 150 °C with a 2 mL/min helium flow.

Used Instrumentation

• NETZSCH TG 209 F1 Libra thermogravimetric analyzer
• BRUKER Optics TENSOR FT-IR spectrometer
• NETZSCH QMS 403 Aëolos quadrupole mass spectrometer
• Agilent 7890A gas chromatograph with 5975C quadrupole mass spectrometer

Main Results and Discussion

• TGA-FT-IR revealed a single mass-loss step peaking at 436.6 °C, with concurrent CO₂ evolution and a melting endotherm at 220 °C via c-DTA®; FT-IR spectra matched both PA6 and PA66.
• TGA-MS detected CO₂ and ion currents (m/z 15, 41, 55 for PA6; m/z 17, 54 for PA66). Identification of organic fragments was limited by library matching.
• TGA-GC-MS provided chromatographic separation, identifying caprolactam (dominant PA6 product), cyclopentanone, nitriles, and other cyclic species, confirming a mixture of PA6 and PA66 decomposition products.

Benefits and Practical Applications

Coupled TGA-EGA methods enable simultaneous thermal profiling and chemical identification, streamlining the analysis of complex polymer mixtures. These insights support optimized recycling workflows, quality control, and process development in polymer recovery.

Future Trends and Potential Applications

Advancements in high-resolution mass spectrometry, real-time data processing, and expanded spectral libraries will enhance detection sensitivity and specificity. Integration with artificial intelligence could automate compound identification and facilitate broader applications in waste-stream characterization and materials research.

Conclusion

TGA-GC-MS emerged as the most definitive method for polymer identification in recycled carpet, while TGA-FT-IR and TGA-MS offered rapid screening with some limitations. Overall, TGA-EGA techniques are valuable tools for efficient, detailed analysis of thermal decomposition and composition in polymer recycling.

References

1. Mihut C., Captain D.K., Gadala-Maria F., Amiridis M.D. Review: Recycling of Nylon from Carpet Waste. Polymer Engineering & Science, 41(9):1457–1470 (2001).
2. Arii T., Motomura K., Otake S. Evolved Gas Analysis Using Photoionization Mass Spectrometry, EGA-PIMS: Characterization of Pyrolysis Products from Polymers. Journal of Mass Spectrometry Society of Japan, 59(1):5–11 (2011).
3. Levchik S.V., Weil E.D. Review: Thermal Decomposition of Aliphatic Nylons. Polymer International, 48(7):532–557 (1999).