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The UV Weathering Tester (mwt) is used in more labs throughout the world than any other accelerated weathering tester. In just a few days or weeks, the mwt can reproduce damage that may occur over months or even years outdoors. Long term exposure to sunlight leads to the degradation of plastic materials. In particular, the non-visible uv radiation characterized by short wavelengths is responsible for photo-degradation, a process that generally results in breaking down the polymer chains. This frequently results in a deterioration of the physical properties, changes in color or chalking of the part surface. As an example, films lose their flexibility and disintegrate, garden furniture becomes brittle or stadium seats become chalky. In order to limit or postpone the onset of degradation, several types of uv light stabilizers can be added to the polymer. The most important stabilizer types work by screening out the harmful ultraviolet light – for instance uv absorbers such as benzophenones or small dispersed particles such as carbon black or inorganic pigments. One important factor, when the light stability of a given material or the performance of a uv stabilizer needs to be assessed, is the selection of a suitable test method. Besides outdoor exposure that closely reflects natural weathering conditions but requires long exposure times, artificial weathering tests have been developed using light sources such as xenon arcs or fluorescent lamps under controlled temperature and humidity conditions
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