Analysis of Polyethylene Terephthalate by TG-FTIR

Importance of the Topic

PET is one of the most widely used polyesters in packaging, textiles and engineering applications. Understanding its thermal decomposition behavior and the identity of evolved gases is essential for optimizing manufacturing processes, improving recycling strategies and assessing environmental impact. TG-FTIR offers a powerful approach by coupling gravimetric analysis with infrared spectroscopy for simultaneous quantification and characterization of decomposition products.

Objectives and Study Overview

This work demonstrates the use of TG-FTIR to investigate PET decomposition under inert (nitrogen) and oxidative (air) atmospheres. The main goals are:

• To record thermogravimetric (TG) and derivative (D-TG) curves during a controlled heating program.
• To acquire three-dimensional IR spectra of gases evolved at each temperature stage.
• To identify key volatile species and map their evolution profiles in both atmospheres.

Methodology and Instrumentation

The analysis employed a Shimadzu TG-FTIR system where the TG exhaust is drawn through a heated transfer line into an FTIR gas cell. Experimental parameters:

• Heating: 20 °C/min up to 600 °C, no hold time.
• Atmospheres: nitrogen or air at 50 mL/min flow.
• FTIR gas cell: 10 cm path length, maintained at 200 °C.
• Spectral acquisition: 4 cm⁻¹ resolution, 30 s intervals, using a DLATGS detector.

Key Results and Discussion

Under nitrogen, PET displayed a single major mass‐loss event near 375 °C. The corresponding 3D IR spectra revealed strong absorptions for CO₂ (2361 cm⁻¹) and carbonyl groups (1760 cm⁻¹). Overlay comparisons confirmed benzoic acid as a principal volatile.
In air, two decomposition peaks appeared in the D-TG curve at 440 °C and 570 °C. IR chromatograms showed concurrent CO₂ release and carbonyl evolution. Extracted spectra indicated an early surge of benzoic acid followed by gradual formation of ester compounds in the later oxidation stage.

Benefits and Practical Applications

The TG-FTIR technique provides direct correlation between thermal events and chemical species, offering benefits such as:

• Detailed polymer degradation profiling for quality control.
• Optimization of recycling and thermal recovery processes.
• Assessment of combustion products for environmental safety.

Future Trends and Opportunities

Emerging developments may include advanced transfer-line heating, coupling with mass spectrometry for enhanced species identification and real-time data processing using chemometric algorithms. These improvements will expand the applicability of TG-FTIR in industrial quality assurance and academic research.

Conclusion

The TG-FTIR analysis of PET under nitrogen and air atmospheres effectively linked mass-loss events to specific volatile products, such as CO₂, benzoic acid and esters. This integrated approach enhances the understanding of polymer decomposition mechanisms and supports advances in materials engineering and environmental monitoring.