Polymer photodegradation occurs when UV light from the sun is absorbed by chemical groups in the polymer formation called chromophores. The UV radiation calculated in nanometers (nm) and ranges between 280 and 400, but the most aggressive part of the UVB range is the very short wavelengths between 280 and 315 nanometers. UV stabilizers have been developed and are added to a polymer to inhibit the photoinitiation processes.
There are two types of light stabilizers : Ultraviolet Absorbers and Hindered Amine Light Stabilizers (HALS). UV absorbers are a type of light stabilizer that functions by competing with the chromophores to absorb UV radiation. Absorbers change harmful UV radiation into harmless infrared radiation or heat that is dissipated through the polymer matrix.
HALS are long-term thermal stabilizers that act by trapping free radicals formed during the photo-oxidation of a plastic material and thus limiting the photodegradation process. The ability of Hindered Amine Light Stabilizers to scavenge radicals created by UV absorption is explained by the formation of nitroxly radicals through a process known as the Denisov cycle.