Using UV-2600i Plus to Evaluate Ultraviolet- Degraded Plastics Based on the Hazen Color Scale

Significance of the Topic

The exposure of transparent plastics to ultraviolet radiation leads to irreversible yellowing and reduced mechanical performance. Quantitative color assessment is essential for material development, quality control and service-life prediction in sectors such as automotive, packaging and construction.

Objectives and Study Overview

This study demonstrates a method for evaluating UV-induced yellowing of polycarbonate (PC) and polyethylene terephthalate (PET) using a UV-Vis spectrophotometer combined with an integrating sphere. Color changes are expressed in Hazen units, enabling simple, standardized comparisons over accelerated weathering times of up to 30 hours.

Methodology and Instrumentation

Samples of PC and PET were exposed to continuous UV irradiation in an accelerated weathering tester, simulating approximately seven months of natural sunlight over 30 hours. Total UV transmittance spectra were recorded between 380 and 780 nm at 1 nm intervals, using a 5 nm slit width and medium scan speed. An ISR-2600Plus integrating sphere attached to a UV-2600i Plus spectrophotometer captured scattered and direct light. Measurement baselines were obtained without samples, followed by sequential spectra collection after specified irradiation intervals.

Main Results and Discussion

Unirradiated PC and PET both show high transmittance across the visible range. With increasing UV exposure, both plastics exhibit a progressive drop in transmittance below 600 nm, indicating yellowing. After 30 hours, PC transmittance at 380 nm fell to roughly 30 % of its initial value, while PET showed even greater losses.

• An overlay comparison revealed PC maintains higher short-wavelength transparency than PET.
• Hazen unit values, computed by LabSolutions UV-Vis Color software, rose linearly with irradiation time for PC, from near zero to approximately 300 units over 30 hours.
• PET displayed a faster initial increase in Hazen units, leveling off beyond 20 hours, indicating a different degradation kinetics.

Practical Benefits and Applications

The described approach offers a straightforward workflow for quantifying plastic yellowing without preparing multiple color standards. It supports routine quality checks in manufacturing lines, comparative aging studies and compliance testing against industry standards.

Future Trends and Potential Applications

• Integration of real-time monitoring systems for in-situ color tracking during outdoor exposure.
• Development of advanced software modules to correlate color metrics with mechanical or chemical degradation data.
• Extension of the method to other polymer types and composite materials for broader industrial adoption.

Conclusion

A UV-Vis spectrophotometer with an integrating sphere and Hazen scale analysis provides a reliable and efficient means to track UV-induced yellowing in PC and PET. The method distinguishes differences in degradation rates and offers actionable data for material evaluation and process control.

Instrumentation Used

• Shimadzu UV-2600i Plus UV-Vis Spectrophotometer
• ISR-2600Plus Integrating Sphere Attachment
• Iwasaki Electric Accelerated Weathering Tester

References

• ISO 6271:2015 Clear liquids — Estimation of colour by the platinum-cobalt colour scale
• JIS K0071-1:2017 Test methods for colour of chemical products — Part 1: Estimation of colour in Hazen units
• ASTM D1209-05(2019) Standard Test Method for Color of Clear Liquids (Platinum-Cobalt Scale)