Analysis Examples Using Carrier Gas Selector Part 4: Pyrolysis of Polyethylene (PE) in Air

Importance of the Topic

Pyrolysis gas chromatography mass spectrometry is a key technique for characterizing polymer structure and assessing degradation products. Comparing pyrolysis under inert and oxidative atmospheres provides insights into chain scission mechanisms and oxidation pathways relevant to materials science, environmental monitoring and quality control in industry.

Objectives and Study Overview

This work demonstrates flash pyrolysis of polyethylene at 550°C in both helium and air using a carrier gas selector system. The goal is to contrast the pyrolysis products formed under inert versus oxidative conditions and to evaluate the applicability of this approach for polymer and environmental analysis.

Methodology and Instrumentation

Flash pyrolysis was performed at 550°C using a Carrier Gas Selector CGS-1050E equipped with a Selective Sampler SS-1010E and MicroJet Cryo Trap MJT-1030E. Pyrolyzates were transferred to a GC/MS for analysis. The GC was fitted with a 30 m Ultra ALLOY-5 column (5 percent diphenyldimethylpolysiloxane, 0.25 mm i.d., 0.25 µm film). Oven programming ranged from 40°C (1 min hold) to 320°C at 20°C per minute. Helium served as the carrier gas at 1 ml/min column flow and total flow of 60 ml/min. Injection port temperature was 320°C and sample size was approximately 30 µg.

Main Results and Discussion

Under helium atmosphere the pyrogram shows a series of hydrocarbon fragments including diolefins, olefins and normal paraffins arising from random chain scission and disproportionation of polyethylene. In contrast, pyrolysis in air yields carbon dioxide and a homologous series of aldehydes from C10 to C15, reflecting thermal oxidation pathways. The presence of CO2 confirms extensive oxidative cleavage, while the aldehyde distribution highlights sequential breakdown of the polymer backbone.

Benefits and Practical Applications

• Enables selective analysis of purely thermal versus oxidative decomposition products
• Supports detailed polymer characterization for research and QA/QC
• Offers a route to monitor environmental oxidative degradation of plastics
• Facilitates identification of functional group products in complex matrices

Future Trends and Potential Applications

Integration of variable atmosphere pyrolysis with high resolution mass spectrometry will enhance structural elucidation of polymers and additives. Advances in cryo trapping and automated carrier gas switching may enable real time monitoring of oxidative degradation. Applications are expected to expand into forensic polymer analysis, recyclability assessment and kinetic studies of oxidative aging.

Conclusion

The use of a carrier gas selector for flash pyrolysis GC/MS provides a flexible platform to discriminate between thermal and oxidative decomposition pathways in polyethylene. This approach yields complementary product profiles that enhance polymer characterization and environmental analysis capabilities.

References

Hosaka et al 5th Polymer Analysis Symposium II-4 p43-44 2000