Pyrolysis ramp rate comparison with Polystyrene and Polycarbonate

Significance of the topic

Hyphenating pyrolysis with gas chromatography offers a versatile and cost-effective approach to polymer analysis. By varying the pyrolysis temperature ramp rate, this method enhances the detection and resolution of both volatile and high molecular weight decomposition products. Eliminating heated transfer lines and switching valves reduces sample loss and simplifies the setup, making it attractive for laboratories handling diverse polymer materials.

Objectives and study overview

This application note evaluates the influence of pyrolysis inlet ramp rates on the chromatographic behavior of polystyrene and polycarbonate samples. Key goals include:

• Comparing the effects of 5 to 60 °C/s ramp rates on retention times, peak areas, and heights.
• Assessing the potential of fast ramp rates to improve characterization of polymer decomposition products.
• Demonstrating the simplicity and efficiency of an OPTIC-4 multi-mode inlet for pyrolytic analysis.

Methodology

Sample preparation involved dissolving polystyrene and polycarbonate in dichloromethane and injecting 1 µl of each solution. Pyrolysis was performed using an OPTIC-4 inlet with ramp rates set to 5, 10, 20, 30, and 60 °C/s, reaching a final temperature of 600 °C. Thermal treatment products were separated on a GL Sciences InertCap 5 MS/Sil (30 m × 0.25 mm, 0.25 µm) column and detected by a Shimadzu QP2010 GC-MS. The GC oven was programmed from 45 °C (3 min hold) to 340 °C at 15 °C/min, and mass spectra were recorded from m/z 50 to 400 in full scan mode.

Instrumentation

• OPTIC-4 Multi Mode Inlet with DMI taper liner
• Shimadzu QP2010 GC-MS
• GL Sciences InertCap 5 MS/Sil column (30 m × 0.25 mm, 0.25 µm)
• CombiPAL autosampler

Main results and discussion

Polystyrene pyrolysis yielded styrene monomer with slight retention time shifts: faster ramps decreased RT from 7.345 min (5 °C/s) to 7.103 min (60 °C/s). Peak heights increased at higher ramp rates despite some variability in areas. For polycarbonate, major decomposition products (bisphenol A, p-isopropenyl phenol, and phenol) exhibited enhanced peak intensities and sharper peaks under 30–60 °C/s conditions. Overall, faster ramps improved chromatographic efficiency, particularly for higher molecular weight components, by minimizing band broadening and reducing secondary reactions.

Benefits and practical applications

• Enhanced detection of high molecular weight pyrolysates for polymer composition and quality control.
• Reduction of sample transfer losses due to absence of heated transfer lines and valves.
• Cost-effective and flexible setup suitable for routine QA/QC and research laboratories.
• Rapid analysis throughput enabled by fast temperature ramps.

Future trends and applications

Advancements may include coupling fast pyrolysis ramps with high-resolution mass spectrometry and tandem MS for detailed structural elucidation. Automation and kinetic modeling tools could further refine ramp profiles for specific polymer classes. Emerging applications in recycled materials, nanocomposites, and advanced polymers will benefit from rapid, in-depth compositional analysis.

Conclusion

Implementing fast inlet temperature ramp rates in pyrolysis-GC significantly improves chromatographic performance for polymer analysis. The most pronounced benefits are observed for less volatile, high molecular weight fragments. The OPTIC-4 setup delivers a simple, economical, and efficient solution for polymer characterization.

References

1. Iwan Horsting. Pyrolysis ramp rate comparison with Polystyrene and Polycarbonate. Application Note No. 115, GL Sciences B.V., Eindhoven.