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

Importance of the Topic

Ultraviolet exposure causes plastics such as polycarbonate (PC) and polyethylene terephthalate (PET) to yellow and lose mechanical integrity. Quantifying this color change is essential for assessing material performance in automotive components, packaging, and outdoor applications. The Hazen (APHA) color scale provides a standardized measure of yellowing, facilitating quality control, lifetime prediction, and comparison across formulations.

Objectives and Study Overview

This study aimed to evaluate the yellowing of PC and PET exposed to accelerated UV irradiation by:

• Measuring total UV–visible transmittance of degraded samples.
• Calculating Hazen unit values to quantify yellowing.
• Comparing degradation rates between PC and PET over exposure times up to 30 hours (equivalent to ~7 months).

Methodology and Instrumentation

Sample Preparation:

• Flat blocks of PC and PET irradiated in an accelerated weathering tester for 0 to 30 hours.
• Exposure increments: 0, 1, 2, 3, 5, 10, 15, 20, 25, and 30 hours.

Transmittance Measurement:

• Instrument: UV–Vis spectrophotometer UV-2600i Plus equipped with ISR-2600Plus integrating sphere.
• Wavelength range: 380–780 nm, interval 1 nm.
• Slit width: 5.0 nm; scanning speed: medium.

Data Analysis:

• LabSolutions UV-Vis Color software calculated Hazen units based on total transmittance spectra.

Main Results and Discussion

1. Transmittance Spectra Trends:

• Unirradiated PC and PET showed high, nearly constant transmittance above 450 nm.
• UV irradiation progressively reduced transmittance below 600 nm, with PC falling to ~30% at 380 nm after 30 hours.
• PET exhibited greater scattering and lower transmittance than PC across wavelengths, indicating higher susceptibility.

2. Comparative Degradation:

• Overlay of transmittance spectra demonstrated that PET yellowed more rapidly and intensely than PC under identical UV exposure.

3. Hazen Scale Evaluation:

• Hazen unit values increased linearly with irradiation time for PC.
• PET’s Hazen values rose faster initially but growth slowed after 20 hours, suggesting saturation of yellowing.

Benefits and Practical Applications

The described approach enables laboratories to:

• Quantify yellowing without preparing multiple color standards.
• Implement rapid, reproducible assessments using a single integrating sphere setup.
• Support quality control in material manufacturing and weathering studies.

Future Trends and Potential Applications

Advances and extensions may include:

• Integration of real-time monitoring in outdoor aging chambers.
• Development of predictive models correlating Hazen units with mechanical and chemical degradation.
• Application to other polymers, coatings, and recycled materials.
• Coupling spectrophotometric data with machine learning for automated quality assessment.

Conclusion

UV–Vis spectrophotometry with an integrating sphere and Hazen scale analysis effectively quantifies plastic yellowing. Results show PET degrades faster than PC under UV light. LabSolutions UV-Vis Color streamlines Hazen unit calculations, enhancing throughput in analytical and quality-control laboratories.

References

1. ISO 6271:2015 Clear Liquids — Estimation of Colour by the Platinum-Cobalt Colour Scale
2. JIS K0071-1:2017 Test Methods for Colour of Chemical Products — Part 1: Estimation of Colour in Hazen Units (Platinum-Cobalt Colour Scale)
3. ASTM D1209-05(2019) Standard Test Method for Color of Clear Liquids (Platinum-Cobalt Scale)