A light stabilizer serves as an additive in polymer-based products such as plastics, rubber, coatings, and synthetic fibers. Its primary function lies in intercepting or absorbing ultraviolet (UV) radiation, neutralizing singlet oxygen, and breaking down hydroperoxide into inactive compounds. This action effectively mitigates or delays potential light-induced chemical reactions within polymers, thereby preventing or slowing processes like photooxidation and extending the overall lifespan of polymer products when exposed to light.,
The detrimental effects of ultraviolet radiation on polymers:
Solar light, which consists of electromagnetic waves, undergoes filtration upon passing through space and the ozone layer. Consequently, the radiation reaching the Earth's surface falls within the 290-3000 nm range. Visible light (400-800 nm) accounts for approximately 40%, while infrared light (800-3000 nm) comprises about 55%. Ultraviolet radiation, spanning 290-400 nm, constitutes a mere 5% of sunlight but carries substantial energy. Absorption of UV rays by polymer products triggers self-oxidation and degradation, resulting in the rupture of chemical bonds, breakage, and cross-linking. These processes lead to noticeable alterations in color, strength, and lifespan, collectively referred to as photoredox or photoaging.
Mechanism of action of light stabilizers:
Light stabilizers exhibit diverse structures and functions. Some are designed to shield, reflect, or absorb UV rays, converting them into harmless heat energy. Others work by quenching the excited states of molecules induced by UV radiation, returning them to ground states and thereby reducing the likelihood of photoredox reactions. Additionally, certain stabilizers capture free radicals generated by photoredox processes, preventing their participation in aging reactions and effectively safeguarding polymer products from UV-induced damage.