Selection of Light Stabilizers

Light Stabilizer Selection
The following factors should be considered when selecting a light stabilizer:

1. Effective absorption of ultraviolet light at 290—400nm wavelength, or the ability to quench the energy of excited-state molecules, or the ability to capture free radicals;

2. Good inherent light stability and thermal stability;

3. Good compatibility, with no exudation during use;

4. Resistance to hydrolysis and extraction by water and other solvents;

5. Low volatility and low pollution;

6. Non-toxic or low-toxic, inexpensive and readily available. 
  Light stabilizers can be divided into four categories:

(1) Light screening agents, mainly including carbon black, zinc oxide, titanium dioxide, and lithopone;

(2) UV absorbers: the most widely used industrially are benzophenones, salicylates, and benzotriazoles;

(3) Quenchers: mainly metal complexes, such as organic complexes of nickel, cobalt, and iron;

(4) Free-radical scavengers: mainly hindered amine derivatives. 
Among them, light screening agents reflect or absorb solar UV radiation, that is, they set up a barrier between the polymer and the light source, blocking ultraviolet light from penetrating into the polymer interior, thus protecting the polymer. UV absorbers are a class of organic compounds that selectively and strongly absorb the solar UV light harmful to polymers while possessing high inherent light resistance. Quenchers are a class of light stabilizers that can effectively transfer the excited-state energy of photosensitive chromophores in polymers and dissipate it in a harmless form, thereby protecting the polymer from photodegradation. Free-radical scavengers achieve their effect by capturing and eliminating free radicals to cut off the auto-oxidation chain reaction.