Analysis of Polyethylene Terephthalate by TG-FTIR

Importance of the Topic

Thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy (TG-FTIR) offers a powerful approach to monitor polymer degradation processes by simultaneously measuring mass loss and identifying evolved gases. This technique is essential for quality control, recycling evaluation, and environmental impact studies of materials like polyethylene terephthalate (PET).

Objectives and Study Overview

The study demonstrates the application of TG-FTIR to characterize the thermal decomposition behavior of PET under inert (nitrogen) and oxidative (air) atmospheres. It aims to correlate mass change profiles with spectral signatures of decomposition products.

Methodology and Instrumentation

The analysis was conducted using the following conditions:

• Sample: ~12–14 mg of PET
• Heating rate: 20 °C/min to 600 °C
• Atmospheres: nitrogen and air, 50 mL/min flow
• Transfer line and gas cell temperature: 200 °C
• IR cell path length: 10 cm, internal diameter suited for standard DLATGS detector
• FTIR parameters: 4 cm⁻¹ resolution, 30 s spectral interval

Key Results and Discussion

Under nitrogen, PET exhibited a single major mass-loss event around 380–400 °C, with FTIR detecting CO₂ (2361 cm⁻¹) and carbonyl-containing fragments indicative of benzoic acid formation. In air, two distinct decomposition peaks at ~440 °C and ~570 °C appeared; FTIR spectra confirmed CO₂ evolution and revealed both benzoic acid and secondary ester compounds. IR chromatograms provided time-resolved absorbance profiles aligned with derivative TG peaks.

Benefits and Practical Applications

• Rapid identification of volatile decomposition products
• Enhanced understanding of thermal stability and degradation pathways
• Applicable to polymer recycling and materials research
• Supports environmental emission analysis during thermal treatment

Future Trends and Potential Applications

Advancements may include integration with mass spectrometry, expanded spectral libraries for comprehensive gas identification, real-time process monitoring in industrial settings, and application to complex polymer blends and composites.

Conclusion

TG-FTIR has been validated as an effective, dual-mode approach to quantitatively and qualitatively analyze PET thermal decomposition. The combined data offer detailed insights into reaction pathways under varying atmospheres, supporting both research and industrial quality-control needs.