Thermal Degradation of Polymers in Air

Significance of the Topic

The study of polymer thermal degradation in a reactive atmosphere addresses crucial questions in material stability, combustion behavior and environmental impact. Understanding oxidative breakdown pathways enables accurate assessment of polymer lifespan, toxicity of decomposition products and performance under real-world conditions.

Objectives and Overview

This application note explores differences between true pyrolysis of polymers under inert gas and oxidative pyrolysis in air. Using a specialized pyrolysis device with gas‐switching capability, the research focuses on polyethylene degradation at elevated temperatures to identify additional oxygen‐derived products and compare them with those formed in helium.

Methodology and Instrumentation

The investigation employed a pyroprobe system with separate purge and carrier gas streams. Key steps:

• Sample heating at 800 °C for 10 s in helium or in air.
• Collection of volatiles on a Tenax cold trap at 35 °C.
• Transfer of trapped compounds into GC by desorption at 280 °C.

The gas chromatograph featured a 50 m × 0.25 mm SE-54 column and FID detection. The GC temperature program held 50 °C for 2 min then ramped at 8 °C/min to 290 °C. Inlet conditions were 300 °C with a 60:1 split.

Main Results and Discussion

Under inert pyrolysis, GC traces displayed homologous triplets of alkadienes, alkenes and alkanes increasing by one carbon per group. Oxidative degradation in air preserved these hydrocarbon series but introduced two additional peaks following each alkane. These correspond to straight‐chain alcohols and aldehydes formed by oxygen‐mediated chain scission and oxidation. The relative intensities of hydrocarbon and oxygenated products varied with heating rate and temperature, indicating competition between pyrolysis and oxidation pathways.

Benefits and Practical Applications

Oxidative pyrolysis analysis offers:

• Insight into polymer aging and weathering under atmospheric exposure.
• Data for fire and combustion modeling by identifying flammable and toxic products.
• Quality control measures for polymer manufacturing and additives evaluation.

Future Trends and Opportunities

Integrating oxidative pyrolysis with mass spectrometry or infrared detection will enhance compound identification. Coupling real‐time analysis and advanced data processing can track kinetics of oxidation. Expanding studies to diverse polymer classes and blended materials will refine predictions of environmental fate and safety.

Conclusion

Reactive‐atmosphere pyrolysis reveals oxygen‐specific degradation products, complementing inert pyrolysis studies. The described gas‐switching pyroprobe and GC method effectively differentiate hydrocarbon and oxygenated fragments, supporting applications in polymer stability, combustion research and regulatory compliance.

References

1. J. Chien and J. Kiang, Oxidative Pyrolysis of Poly(propylene), Makromol. Chem. 181, 47–57 (1980).
2. T. Wampler and E. Levy, Effects of Slow Heating Rates on Products of Polyethylene Pyrolysis, Analyst 111, 1065–1067 (1986).
3. T. Wampler and E. Levy, Effect of Heating Rate on Oxidative Degradation of Polymeric Materials, J. Anal. Appl. Pyrol. 8, 153–161 (1985).