Stability to Sunlight and UV Radiation

Unstabilised PE very rapidly becomes brittle when exposed (prolonged exposure) to sunlight, caused mainly by UV radiation. Degradation is accompanied by marked deterioration in mechanical properties, gloss loss, and cracking. 

Light stabilisers (photostabilisers) are chemical compounds that interfere in the physical and chemical processes of light-induced degradation. The service life of unprotected PE in the dark at 20 °C is 8-10 years, and that of stabilised or crosslinked PE in moderate climates is 15-20 years. In tropical climates the service life is only two to five years, even if the products (pipes, tubes) contain stabilisers ( 2%) the lifetime of films is only three months. 

There are four classes of light stabilisers having different modes of action. These are discussed next. 

Combined formulations of light stabilisers and antioxidant systems are more effective in photostabilisation. The most efficient are combinations of nickel-containing light stabilisers and HAS with UV absorbers. Some application fields require the incorporation in LDPE films of certain fillers, for example, china clay, talc, and chalk. These fillers have a pronounced antagonistic effect on the light stability of the films, which is attributed mainly to transition metals present in the fillers as impurities. An increased concentration of light stabilisers is necessary in these cases. 

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