UV ABSORBERS & ANTIOXIDANTS
UV absorbers are used frequently in plastics, including cosmetics and films. Different UV stabilizers are utilized depending upon the substrate, intended functional life, and sensitivity to UV degradation.
UV (Ultraviolet) absorbers, such as benzophenones, work by absorbing the UV radiation and preventing the formation of free radicals.
Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent, producing free radicals. In turn, these radicals can start chain reactions which cause damage to the material. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions. They do this by being oxidized themselves, so antioxidants are often reducing agents such as polyphenols.
Polymers containing double bonds in their main chains, such as natural rubber and polybutadiene, are especially susceptible to oxidation. Oxidation and UV degradation are also frequently linked, mainly because UV radiation creates free radicals by bond breakage. Other polymers susceptible to oxidation include polypropylene and polyethylene. The former is more sensitive owing to the presence of secondary carbon atoms present in every repeat unit with which the radicals formed are more stable than those formed on a primary carbon atom.