Mechanism of UV Absorbers

Mechanism of UV Absorbers
1. The reason why ultraviolet absorbers can absorb ultraviolet light is that the molecules of these compounds contain two parts: the structure of the conjugated π electron system and the structure capable of moving hydrogen atoms. There are also only the first part.
2. The structural molecule of the ultraviolet absorber contains at least one ortho-hydroxyl phenyl substituent. In this type of compound, a chelate ring is formed by the ortho-hydroxyl and a nitrogen atom or an oxygen atom. After absorbing ultraviolet rays, hydrogen bond breakage occurs Isomerization, the thermal vibration of the intramolecular structure occurs, the hydrogen bond is destroyed, the chelating ring is opened, and the intramolecular structure changes, so that harmful ultraviolet light is converted into harmless heat energy, thereby protecting the material.
3. In this process, the chelate ring formed in the molecule is the key to its ability to absorb ultraviolet rays. The energy sensitive range of opening this ring is just the ultraviolet energy range of 290-400nm wavelength.
4. In addition, as an ultraviolet absorber, it must not undergo photochemical reactions under the action of ultraviolet light or visible light; it has good stability to chemicals and water, and good stability to heat; it has low volatility; Good compatibility and no solvent extraction.
Conditions that UV absorbers should have
1. It can strongly absorb ultraviolet rays (especially with a wavelength of 290-400nm);
2. Good thermal stability, even in processing, it will not change due to heat, and the thermal volatility is small;
3. Good chemical stability, no adverse reaction with material components in the product;
4. Good miscibility, can be evenly dispersed in the material, no frost, no leakage;
5. The photochemical stability of the absorbent itself is good, no decomposition, no discoloration;
6. Colorless, non-toxic, odorless;
7. Resistant to soaking and washing;
8. Cheap and easy to get;
9. Insoluble, or hardly soluble in water.