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PMMA and PC undergo photochemical aging leading to a gradual loss of material transparency and appearance during service life, which is desired to reach 50 years or more. Available artificial weathering test methods are unable to distinguish materials in terms of the speed of aging in outdoor use as roof materials. In order to design an appropriate accelerated or time-compressed test method, the 'worst case' scenario of the respective climatic conditions must be found. Therefore, samples of PMMA and PC were exposed to artificial weathering tests using different climatic conditions in terms of relative humidity and surface wetness. In the case of PMMA, it was found that water accelerates the photo degradation enormously. The fastest aging occurred when liquid water and UV radiation acted simultaneously on the sample surface and the PMMA reached its highest water content during weathering. In the case of PC, it was found that both vapour and liquid water speed up the photoaging, similarly to PMMA. But differently from PMMA, the worst case scenario for PC proved to be weathering conditions with high relative humidity. A test method has to be able to run artificial weathering under the different moisture conditions which can occur in the field.
To examine the action of acid atmospheric precipitation on the light stabilisers in automotive coatings two common clearcoat types (TSA and 2K-PU) blended with commercially available HALS and UVA were subjected to artificial weathering (Acid Dew and Fog test and Acid-free weathering test) and natural weathering outdoors in Jacksonville, FL. Tracing gloss and haze during weathering the test results showed that the influence of acid stress on the long-term performance of the clearcoats depended on the kind of the stabilisation system.