Analysis of yellowing of a polyvinyl chloride sheet Part 2: Heart-cut EGA-GC/MS

Significance of the Topic

This study addresses the discoloration, or yellowing, of PVC sheets—a common issue affecting the material’s aesthetics and mechanical integrity. Understanding the underlying degradation mechanisms and additive consumption is crucial for improving polymer longevity in applications ranging from construction to medical devices.

Objectives and Study Overview

The technical note aims to compare volatile compounds released from white and yellowed PVC surfaces using heart-cut evolved gas analysis coupled to GC/MS. Part 2 builds on initial EGA-MS results by selectively trapping and analyzing low-temperature volatiles to pinpoint early-stage degradation pathways.

Methodology

The PVC samples were pyrolyzed from 100 to 220 °C at 20 °C/min. Gases evolving in this range were cryogenically trapped at the head of a UA+-5 capillary column via a MicroJet Cryo-Trap. After trapping, the analytes underwent GC separation and MS detection to generate chromatograms of the white and yellowed surfaces.

Used Instrumentation

• Multi-functional Pyrolyzer with Auto-Shot Sampler
• MicroJet Cryo-Trap for volatile capture
• UA+-5 GC column (5% diphenyl, 95% dimethylpolysiloxane; 30 m × 0.25 mm i.d., 0.25 μm film)
• GC/MS system with split ratio 1:20, column flow 1 mL/min

Main Results and Discussion

Chromatograms reveal that hydrochloric acid (HCl) evolves only from the yellowed PVC, indicating early dehydrohalogenation. Both samples release fragments attributed to the thermal breakdown of methyltin mercaptide stabilizer, but the yellowed surface shows lower relative intensities, reflecting greater stabilizer depletion. These findings demonstrate that low-temperature elimination of HCl accelerates stabilizer consumption and promotes discoloration.

Benefits and Practical Applications

• Enables targeted detection of early PVC degradation products
• Assists in evaluating stabilizer performance under thermal stress
• Supports quality control protocols for long-term PVC stability

Future Trends and Opportunities

Emerging cryo-trapping and multidimensional GC techniques could enhance separation of complex degradation profiles. Advances in high-resolution MS will further resolve minor volatile species, guiding development of more robust stabilization chemistries. Integration with real-time monitoring could offer in-situ degradation tracking in manufacturing lines.

Conclusion

Heart-cut EGA-GC/MS effectively discriminates between white and yellowed PVC surfaces by isolating low-temperature volatiles. The selective detection of HCl and stabilizer fragments highlights early degradation steps, offering a powerful tool for material evaluation and stabilization strategy optimization.

Reference

Frontier Laboratories Ltd. Multi-functional Pyrolyzer Technical Note PYA3-022E. Analysis of yellowing of a polyvinyl chloride sheet Part 2: Heart-cut EGA-GC/MS.