Most products are exposed to sunlight or fluorescent lighting at some time during service. Light can promote degradation, sometimes involving oxygen.
Prolonged exposure to oxygen and light especially with a wavelength between 250nm and 480nm can cause changes in color. It can also cause chalking and cracking and a deterioration in mechanical properties.
Light stabilizers can be added to plastic to protect them from the degradative effects of exposure to sun and weather. It is often advisable to use more than one type of light stabilizer in the same formulation, although they can interact. There are three major classes of light stabilizer for polyolefins:
1. UV absorber: they are low cost, effective stabilizers that function by the absorption of UV light they are effective for short term exposure.
2. Nickel quencher: energy transfer agents that are not in wide use since they contain heavy metal impart color to the final product and are not as effective as the HALS discussed in the next.
3. Hindered amine light stabilizers (HALS): the most effective of the light stabilizers for polyolefins available in the wide range of molecular weight and structures suitable for almost any application. They can also perform as long term thermal stabilizers.