Analysis of yellowing of a polyvinyl chloride sheet Part 1: Evolved gas analysis-MS

Significance of the Topic

The durability and performance of polymeric products are directly affected by chemical degradation processes such as yellowing, which can compromise aesthetics, mechanical properties and ultimately product value. Monitoring such degradation at different service stages is critical for quality control, product development and lifespan prediction in industries relying on polyvinyl chloride (PVC) materials.

Study Objectives and Overview

This study aims to compare the chemical behavior of the white and yellowed surfaces of a PVC sheet using evolved gas analysis–mass spectrometry (EGA-MS). By characterizing the gaseous products released during controlled thermal decomposition, the work seeks to identify differences in degradation pathways and heat resistance between the two surfaces.

Methodology and Instrumentation

The experimental approach involved:

• Sample preparation: Both surfaces of the PVC sheet were pulverized to ~0.2 mg.
• EGA-MS setup: A Multi-Shot Pyrolyzer (EGA/PY-3030D) coupled directly to a gas chromatograph injection port and mass spectrometer detector via a 2.5 m UADTM-2.5N heated transfer tube (0.15 mm i.d.).
• Thermal program: Furnace ramp from 100 to 600 °C at 20 °C/min; GC split ratio 1/50; carrier gas flow 1 mL/min; GC oven held at 300 °C.

Main Results and Discussion

EGA thermograms for both surfaces exhibit two major features:

• A broad desorption peak near 300 °C, identified by m/z 36 as hydrogen chloride (HCl). The yellowed surface releases HCl at lower onset (160 °C) and apex (300 °C) temperatures compared to the white surface (248 °C onset, 308 °C apex), implying reduced thermal stability and earlier dehydrochlorination in the degraded layer.
• A high-temperature degradation peak around 450 °C corresponding to bulk PVC chain scission, which is nearly identical for both surfaces.

The shifted HCl evolution profile on the yellowed side suggests alterations in polymer structure or additive distribution that lower its heat resistance. Further characterization (see PYA3-022E) is needed to elucidate the detailed chemical modifications responsible for discoloration.

Benefits and Practical Applications

This EGA-MS method provides a rapid, quantitative means to detect early-stage degradation of PVC surfaces by monitoring HCl release profiles. Such insights support:

• Quality assurance in manufacturing and aging studies.
• Optimization of stabilizer formulations to mitigate yellowing.
• Predictive maintenance and lifecycle management of PVC-based products.

Future Trends and Opportunities

Advances in pyrolysis interface design, coupling with high-resolution MS and tandem MS approaches will enhance identification of trace degradation products. Integration of machine learning for thermogram pattern recognition could enable automated assessment of polymer aging, enabling real-time quality monitoring in production lines.

Conclusion

Evolved gas analysis–MS effectively differentiates the thermal degradation behavior of white and yellowed PVC surfaces, revealing earlier HCl release in the discolored layer. This analytical strategy offers a sensitive tool for studying polymer deterioration and guiding formulation improvements to extend service life.

Reference

• Frontier Laboratories Ltd. PYA3-021E Multi-functional Pyrolyzer Technical Note: Analysis of yellowing of a polyvinyl chloride sheet Part 1: Evolved gas analysis-MS.
• Frontier Laboratories Ltd. PYA3-022E Multi-functional Pyrolyzer Technical Note.