Fotodegradaatioon

Fotodegradaatioon, commonly referred to as photodegradation, is the chemical and physical alteration of materials caused by exposure to light, especially ultraviolet (UV) radiation. It can occur through direct photolysis, where bonds in a molecule absorb light and break, or through indirect processes such as photooxidation, in which light-activated species like oxygen radicals attack the material. Reactions may produce discoloration, surface cracking, embrittlement, reduced mechanical strength, and changes in texture or gloss.

Mechanisms involved include the absorption of photons by the material or by photosensitizers, followed by energy transfer that generates reactive species. Oxygen, moisture, temperature, and light spectrum influence the rate and pathways of degradation. Some materials degrade slowly under ambient light, while polymers, coatings, dyes, and wood are often more susceptible. In the environment, photodegradation can contribute to the breakdown of pollutants and, for plastics, to fragmentation into microplastics, which may then undergo further chemical or biological processing.

Factors affecting the rate include light intensity and wavelength distribution, exposure duration, and the presence of stabilizers or inhibitors. Protective strategies include UV absorbers, light stabilizers such as hindered amine light stabilizers (HALS), antioxidants, antioxidants, and physical barriers like coatings or opaque packaging. Accelerated weathering tests simulate years of exposure to study durability and predict service life.

Applications and implications span material design, product aging, and environmental remediation, where photocatalysis (for example, using titanium dioxide) can degrade organic pollutants under light.