Evaluation of deterioration degree of exterior wall coatings using Micro-UV Irradiator - Part 1 Acrylic coatings with and without UV absorber and HALS

Importance of the Topic

Acrylic coatings are widely applied on exterior building surfaces for their color rendering and stability. Prolonged UV exposure accelerates photodegradation, leading to aesthetic and structural decline. Incorporating UV absorbers and HALS enhances coating longevity. Evaluating the deterioration process under controlled UV irradiation provides critical insights for material optimization and quality assurance.

Objectives and Study Overview

The study aims to assess the degradation behavior of acrylic coatings with (Sample A) and without (Sample B) UV absorber and HALS under accelerated UV exposure. Using a Micro-UV Irradiator and EGA-MS analysis, the investigation quantifies photostability and degradation kinetics over irradiation periods up to 20 hours.

Methodology

• Sample Preparation: Two test coatings applied to Eco-Cup UV support; Sample A contained Tinuvin 400 (UV absorber) and Tinuvin 292 (HALS); Sample B lacked additives.
• UV Irradiation: Samples irradiated at 60 °C in air for 1–20 hours using a mercury-xenon lamp in the Micro-UV Irradiator.
• Evolved Gas Analysis: Pre- and post-irradiation thermal desorption monitored by EGA-MS under helium; temperature ramp from 100 °C to 700 °C at 20 °C/min.

Used Instrumentation

• Multi-Shot Pyrolyzer EGA/PY-3030D
• Micro-UV Irradiator UV-1047Xe
• UADTM-2.5N analytical column (2.5 m, 0.15 mm i.d.)
• Vent-free GC/MS adapter and Side-hole Eco-Cup UV sample holders

Main Results and Discussion

Sample A demonstrated stable EGA thermogram profiles over 10 hours of UV exposure, with minimal shifts in peak apex temperature and consistent FWHM values. In contrast, Sample B displayed an 8 °C decrease in peak apex temperature and a doubling of FWHM from 31 °C to 70 °C after 10 hours, indicating significant polymer matrix breakdown. FWHM evolution plots confirmed superior durability of stabilized coatings versus unstabilized ones throughout the irradiation series.

Benefits and Practical Applications

• Quantitative assessment of photostabilizer effectiveness in acrylic formulations.
• Rapid evaluation protocol for coating durability in QA/QC and R&D.
• Guidance for optimizing additive concentrations to extend service life.
• Adaptable methodology for weathering tests across various polymer coatings.

Future Trends and Opportunities

Advancements may include coupling EGA-MS with GC/MS for detailed degradation product profiling, integrating real-time monitoring systems, and employing predictive modeling to forecast long-term performance. Exploration of novel stabilizers and nanocomposite additives will further enhance coating resilience under diverse environmental stressors.

Conclusion

EGA-MS analysis coupled with Micro-UV irradiation effectively differentiates between stabilized and unstabilized acrylic coatings, providing a robust framework for evaluating photostability. Incorporation of UV absorbers and HALS significantly mitigates thermal degradation, underscoring their critical role in coating longevity.

References

T. Yuzawa et al., Polymer Degradation and Stability, 96 (2011) 91–96.