[Bite Chemical] About the types of light stabilizers and their mechanisms of action

Ultraviolet radiation can trigger photo-oxidative degradation of polymer materials. Light stabilizers are plastic aids that inhibit or slow down the degradation of polymer materials caused by photo-oxidation. agent. It can shield or absorb ultraviolet energy, quench singlet oxygen and decompose hydroperoxides into inactive substances, etc., so that the polymer can eliminate or slow down the possibility of photochemical reactions under the radiation of light, and prevent or Delay the photoaging process, thereby extending the service life of polymer products. With the rapid development of polymer synthetic materials, especially the increasing use of synthetic materials in outdoor applications, light stabilizers have become an important category of plastic additives and are mainly used in plastics, coatings, rubber, chemical fibers, adhesives and other high-tech applications. Molecular materials and other special polymer materials.

Light stabilizers have different functions due to their different structures and varieties. Some can shield, reflect ultraviolet rays or absorb ultraviolet rays and convert them into harmless heat energy; some can quench the excited state of molecules or groups excited by ultraviolet rays and return them to their ground state, eliminating or slowing down the occurrence of photooxidation. Possibility of reduction reaction; some capture free radicals generated by photooxidation and reduction, thus preventing free radical reactions that cause aging of products and protecting products from ultraviolet damage.

Light stabilizers can be divided into the following categories according to their mechanism of action:

(1) Free radical scavenger: According to the supply of light stabilizer UV-994 Understand that the hindered amine functional group belongs to the alicyclic amine structure. After absorbing light energy in the aerobic state, it can be converted into nitroxide free radicals NO•. These nitroxide free radicals can not only capture the nitric oxide radicals generated during the photo-oxidative degradation of polymer materials. Alkyl active free radicals, and have a regeneration function during the light stabilization process, thus inhibiting chain reactions to achieve protection purposes. Mainly hindered amine light stabilizers (HALS) are the most promising new type of high-efficiency light stabilizers.

(2) Light shielding agent: This is a type of substance that can block or reflect ultraviolet rays, that is, it sets a barrier between the polymer and the light source to prevent ultraviolet rays from penetrating deep into the polymer, thereby playing a role The role of 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.

(3) Ultraviolet absorber: It can effectively absorb ultraviolet rays with a wavelength of 290~410nm, while rarely absorbing visible light. It has good thermal stability and light stability. According to their chemical structure, they can be mainly divided into: o-hydroxybenzophenones, benzotriazoles, salicylates, triazines, and substituted acrylonitriles. Used as an auxiliary light stabilizer and hindered light stabilizer, especially in polyolefins or coatings.

(4) Quencher: It can accept the energy absorbed by the chromophore in the plastic and emit this energy in the form of heat, fluorescence or phosphorescence, thus protecting the polymer from ultraviolet damage. . It has a good stabilizing effect on polymers and is 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.

(5) Hydroperoxide decomposer: It is one of the hindered amine light stabilizers. 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.