Light stabilizers can be divided into the following categories according to the mechanism of action
(1) Light shielding agent: This is a kind of substance that can shield or reflect ultraviolet rays, so that light cannot penetrate into the interior of the polymer, thereby protecting the polymer. Light shielding agents include inorganic pigments such as carbon black and titanium oxide, and organic pigments such as phthalocyanine blue and phthalocyanine green, among which carbon black has the best shielding effect.
(2) Ultraviolet absorber: Its function can effectively absorb ultraviolet rays with a wavelength of 290~410nm, but rarely absorb visible light, and it has good thermal stability and light stability. According to its chemical structure, it can be divided into: o-hydroxybenzophenones, benzotriazoles, salicylates, triazines and substituted acrylonitriles. Used as auxiliary light stabilizer and hindered light stabilizer, especially in polyolefins or coatings.
(3) Quencher: It can accept the energy absorbed by the chromophore in the plastic and emit the energy in the form of heat, fluorescence or phosphorescence, thereby protecting the polymer from UV damage. It has a good stabilization effect on polymers and is mostly used in films and fibers. Mainly some divalent organic nickel chelates. Organonickel light stabilizers have good performance, but may be replaced by other nontoxic or low toxicity quenchers due to the toxicity of heavy metal ions.
(4) Free radical scavenger: This type of light stabilizer can capture the active free radicals generated in the polymer, thereby inhibiting the photooxidation process and achieving the purpose of light stabilization. Mainly hindered amine light stabilizers (HALS). It is the most promising new type of high-efficiency light stabilizer, and the average annual demand growth rate in the world is 20% to 30%.
(5) Hydroperoxide decomposer: It is one of hindered amine light stabilizers. Polymers can generate hydroperoxides during storage and processing, resulting in photo-oxidative degradation of polymers, and hydroperoxide decomposers can decompose peroxides, generate stable nitrogen-oxygen radicals, and further capture free radicals , thereby inhibiting polymer degradation.