Quantitative Analysis of Anti-Degradant Additive (6PPD) in Tire Rubber Using Pyrolysis-GC-MS

Importance of the Topic

6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) is a key antioxidant additive in tire rubber, extending product life by preventing oxidative degradation.
When released into the environment as tire road wear particles (TRWP), 6PPD converts to the toxic 6PPD-quinone, posing serious risks to aquatic life and ecosystems.
Accurate measurement of 6PPD levels in rubber materials is essential for assessing environmental impact and guiding the development of more sustainable additives.

Objectives and Study Overview

This work demonstrates a rapid, pretreatment-free method for quantitative analysis of 6PPD in tire rubber using pyrolysis-GC-MS (Py-GC-MS).
The study aims to identify and quantify 6PPD directly from rubber fragments, establish method performance metrics, and illustrate the practical reliability of the approach.

Methodology and Instrumentation

Sample Preparation:

• Calibration standards: 1 µL of 10 000 ng/µL 6PPD in toluene mixed with 20 µL styrene-butadiene rubber (SBR) solution to mimic sample matrix.
• Sample: ~0.5 mg tire rubber fragment placed into a sample cup with glass wool, no chemical pretreatment.

Analysis Workflow:

• Evolved Gas Analysis-MS (EGA-MS) to determine optimal thermal desorption profile.
• Thermal Desorption (TD)-GC-MS using Shimadzu GCMS-QP2020 NX:
   • Desorption ramp from 60 °C to 370 °C at 20 °C/min.
   • GC column: SH-5Sil MS (30 m × 0.25 mm × 0.25 µm).
   • Carrier gas: He, constant linear velocity 40.0 cm/s. Split injection (15:1).
   • MS detection: EI ionization, scan m/z 44–500.

Instrumentation Used

• Pyrolyzer: EGA/PY-3030D Multi-Shot with AS-1020E Auto-Shot Sampler.
• Gas chromatograph mass spectrometer: Shimadzu GCMS-QP2020 NX.

Main Results and Discussion

Qualitative Identification:

• Total ion chromatogram of tire extract showed a peak at ~10.43 min.
• Spectral library search (NIST-23 and Shimadzu Polymer Additives Library) confirmed the peak as 6PPD (trade name Nocrac 6C).

Quantitative Performance:

• Quantifier ion: m/z 211; reference ion: m/z 268, selected for high signal and low matrix interference.
• Calibration range 50–1000 ng, external standard linearity R2 > 0.9993.
• Repeatability from seven replicates at 50 ng: RSD = 3.3 %.
• Limit of detection (LOD): 3.0 ng; limit of quantification (LOQ): 10.2 ng.

Sample Analysis:

• Measured 6PPD content in tire rubber: 1200 mg/kg.

Benefits and Practical Applications

• Minimal sample preparation: direct analysis of rubber fragments without extraction.
• Matrix-matched calibration ensures reliable quantification.
• Rapid identification of additives via polymer additive spectral library.
• Sensitive detection suitable for environmental and quality control laboratories.

Future Trends and Opportunities

Expanding the method to monitor 6PPD transformation products and alternative antioxidants in diverse polymer matrices.
Integration with high-resolution MS for simultaneous screening of multiple tire wear compounds.
Development of standardized protocols for environmental monitoring of TRWP and associated toxicants.

Conclusion

The described Py-GC-MS approach provides a fast, reliable, and sensitive protocol for quantifying 6PPD in tire rubber.
Method performance metrics (linearity, repeatability, LOD/LOQ) meet practical requirements for research and routine analysis.
Shimadzu’s Polymer Additives Library streamlines qualitative identification, supporting the development of safer rubber additives.

Reference

• Tian et al., Science, 371 (2021) 185-189.
• ISO/TS 21396:2017, Determination of mass concentration of tire and road wear particles in soil and sediments by Py-GC-MS.