(1) Light shielding agents: These are substances that can shield or reflect ultraviolet rays, preventing light from penetrating into the interior of polymers, thereby protecting polymers. 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 absorbers: They can effectively absorb ultraviolet rays with a wavelength of 290~410nm, but rarely absorb visible light. They have good thermal stability and light stability. According to their chemical structure, they can be mainly divided into: o-hydroxybenzophenone, benzotriazole, salicylate, triazine, and substituted acrylonitrile. They are used together as auxiliary light stabilizers and hindered light stabilizers, especially in polyolefins or coatings.
(3) Quenchers: They can accept the energy absorbed by the chromophore in the plastic and dissipate the energy in the form of heat, fluorescence or phosphorescence, thereby protecting the polymer from damage by ultraviolet rays. They have a good stabilizing effect on polymers and are mostly used in films and fibers. Mainly some divalent organic nickel chelates. Organic nickel light stabilizers have good performance, but due to the toxicity of heavy metal ions, they may be replaced by other non-toxic or low-toxic quenchers.
(4) Free radical scavengers: This type of light stabilizer can capture active free radicals generated in polymers, 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, with an average annual demand growth rate of 20%~30% internationally.
(5) Hydroperoxide decomposer: It is a type of hindered amine light stabilizer. Polymers can produce hydroperoxides during storage and processing, leading to photooxidative degradation of polymers. Hydroperoxide decomposers can decompose peroxides to generate stable nitrogen-oxygen free radicals and further capture free radicals, thereby inhibiting polymer degradation.