Analysis of Acrylonitrile Butadiene Rubber (NBR) by Double-Shot Technique

Analysis of Acrylonitrile Butadiene Rubber (NBR) by Double-Shot Pyrolyzer® Technique

Importance of the Topic

The characterization of polymeric materials such as NBR is complicated by the presence of both base polymer decomposition products and low-molecular-weight additives. Conventional single-shot pyrolysis delivers a single chromatogram mixing volatiles, additives and polymer fragments, hindering clear component identification. The double-shot approach separates volatile additives from polymer pyrolysis products, improving analytical clarity and reliability in industrial QA/QC, materials research and regulatory compliance.

Aims and Study Overview

This application note demonstrates the use of a two-step pyrolysis technique to distinguish additives from the main polymer structure in NBR. The study compares pyrograms obtained by single-shot and double-shot modes, illustrating how thermal desorption followed by pyrolysis yields cleaner, more interpretable chromatograms.

Methodology and Instrumentation

Thermal Desorption (First Stage):

• Temperature program: 100 °C ramped to 300 °C at 20 °C/min, held for 5 min.
• Goal: selective elution of volatile additives (e.g., dioctyladipate, dioctylphthalate, dioctyl sebacate).

Instant Pyrolysis (Second Stage):

• Pyrolysis temperature: 550 °C.
• Rapid decomposition of the basic NBR polymer matrix.

Instrumentation:

• Double-Shot Pyrolyzer (PY-2020D).
• Mass spectrometer detector (m/z 29–400).
• GC column: Ultra ALLOY-5 (5 % phenyldimethylpolysiloxane), 30 m × 0.25 mm × 0.25 µm.
• Carrier gas: Helium, column flow 1.0 mL/min, total flow 100 mL/min.
• GC oven program: 40 °C (3 min), 10 °C/min to 300 °C (3 min).
• Injection port: 320 °C; sample mass ~0.3 mg.

Main Results and Discussion

Single-shot pyrograms combine additive peaks with polymer pyrolysates, complicating peak assignment. In contrast, the double-shot technique yields two distinct chromatograms: the first stage shows only additive peaks (DOA, DOP, DOS), while the second stage reveals polymer decomposition products without interference. This separation enhances confidence in identifying polymer fragments and quantifying additive content.

Benefits and Practical Applications

The double-shot method offers:

• Improved peak resolution between additives and polymer fragments.
• Faster, more accurate QA/QC workflows in rubber manufacturing.
• Enhanced capability to screen unknown samples for residual additives or degradation markers.

Future Trends and Potential Uses

Advances may include coupling double-shot pyrolysis with multidimensional GC or high-resolution MS to further improve separation and identification of complex polymer additives. Integration with automated EGA-guided temperature profiling can optimize desorption/pyrolysis parameters for new polymer systems. Expanded applications are expected in recycling, environmental monitoring of polymer breakdown products, and forensic analysis of elastomers.

Conclusion

Double-shot pyrolysis delivers a clear analytical advantage over single-shot methods for NBR, enabling the selective removal of additives followed by precise polymer decomposition analysis. This technique streamlines interpretation of complex pyrograms and supports robust materials characterization.

Reference

• Application Note PYA3-001E: Evolved Gas Analysis methods for determining optimal desorption and pyrolysis conditions.