The most important UV-degradation mechanisms for polymers are photolysis and photo-oxidation. For polyolefins it is well known that photo-oxidation is the dominating mechanism. These polymers do not have an inherent absorption at wavelengths present in terrestrial sunlight (>290 nm) so photolysis cannot play an important role. In contrast to polyolefins, the majority of engineering plastics do have absorptions at these wavelengths. As a result, for these polymers, besides photo-oxidation, photolysis can play an important role. For polyamide 6, poly(butylene terephthalate), two different copolyetheresters and bisphenol-A polycarbonate, the importance of photolysis as well as that of photo-oxidation in polymer light-induced degradation is discussed.
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