photostabilizers

Photostabilizers are additives used to protect polymers and coatings from light-induced degradation, especially from ultraviolet (UV) radiation. They function by absorbing UV energy, quenching excited states, or scavenging reactive species formed during photooxidation, thereby reducing chain scission, discoloration, and loss of mechanical properties.

The main classes are UV absorbers and HALS. UV absorbers (UVAs) such as benzotriazoles, benzophenones, and triazines absorb UV photons and convert the energy into heat, preventing excited states from triggering degradation. HALS, or hindered amine light stabilizers, do not primarily absorb UV but suppress radical reactions formed during photodegradation by scavenging alkyl and peroxy radicals and by facilitating the repair or stabilization of the polymer chain.

In practice, photostabilization often relies on combinations of UV absorbers, HALS, and antioxidants, chosen to suit the polymer, processing conditions, and end-use environment. The mechanisms are often synergistic, with UV absorbers protecting against initial photochemical events and HALS mitigating radical-driven damage that follows.

Applications include plastics (such as PVC, polyolefins, and polyesters), packaging films, coatings, and automotive and electronic components, as well as cosmetics packaging and other photostable surface finishes. Important considerations include compatibility with the host polymer, optical properties like color and transparency, processing temperatures, and potential migration of additives. Regulatory and environmental concerns are also relevant, as some UV absorbers can migrate or be subject to restrictions due to toxicity or persistence.