A brief approach for establishing the correlation between natural & accelerated weathering of plastics

Introduction:The weathering of plastics consists of photochemical and thermal breakdown caused by sunlight, heat, moisture, and oxygen. The impact of weathering on plastics causes a decline in multiple characteristics. Consequently, understanding the impact of weathering on plastics is crucial prior to suggesting their appropriateness for different outdoor uses. However, outdoor weathering studies are time-consuming activities. To minimize outdoor testing time, an accelerated test is conducted under simulated conditions. This aids in forecasting the long-term outdoor resilience of plastics based on the known connection between short-term accelerated laboratory test results and natural weathering data

Approach:
The approach for establishing the relationship should be as follows

- First sample to be exposed to natural and accelerated weathering.
- Then degradation of properties to be measured (mechanical, optical, chemical, physical).
- After that dose-response models D= k(E.t) n to be used to relate UV exposure to degradation.
- Next step is, determining acceleration factors by comparing time or UV dose required to reach the same degradation.
- Finally, models like Arrhenius equation for temperature-driven degradation should be applied.

Key Tools & Methods: The machinery and methods of testing used for this study are given below.
- Accelerated devices: QUV, Xenon Arc, Weatherometers.
- Standards: ASTM D4329, ISO 4892.
- Validation through long-term natural exposure and data fitting.

Challenges: The weathering study is not simple since it involves so many governing factors. Therefore, it is a complex phenomenon. It is complex because of the following:
- Environmental variability in natural weathering.
- Non-linear degradation mechanisms.
- Complex interaction of UV, heat, and moisture.
- Therefore, combination of modelling (theoretical) and experimental verification is essential.

Conclusion:
An integrated experimental and modelling method enables precise lifetime forecasting of plastics by bridging natural and accelerated weathering data.

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Author
Dr. Subhas C. Shit

Ex principal Director - Central Institute of Plastics Engineering & Technology
(CIPET - Ministry of Chemicals & Fertilizers, Govt. of India)