Introduction and applications of several common UV absorbers

　　A UV absorber is a kind of light stabilizer that absorbs ultraviolet rays from sunlight and fluorescent light sources without changing itself. Plastics and other polymeric materials, under the action of ultraviolet rays from sunlight and fluorescence, undergo autoxidation, leading to polymer degradation and deterioration, resulting in poor appearance and mechanical properties. Adding a UV absorber can selectively absorb this high-energy ultraviolet light, converting it into harmless energy that is released or consumed.

　　Different types of polymers have different ultraviolet wavelengths that cause deterioration. Different UV absorbers can absorb different wavelengths of ultraviolet light. When using them, the UV absorber should be selected according to the type of polymer.

　　A UV absorber should meet the following conditions: ① It can strongly absorb ultraviolet rays (especially ultraviolet rays with a wavelength of 290-400 nm); ② It has good thermal stability and will not change due to heat even during processing, and has low thermal volatility; ③ It has good chemical stability and does not react unfavorably with the material components in the product; ④ It has good miscibility and can be uniformly dispersed in the material without frosting or bleeding; ⑤ The photochemical stability of the absorber itself is good, it does not decompose, and does not change color; ⑥ It is colorless, non-toxic, and odorless; ⑦ It is resistant to washing; ⑧ It is inexpensive and readily available.

　　UV absorbers can be classified into the following categories according to their chemical structure: salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, triazines, and others.

　　No.1

　　Phenyl salicylate

　　Component: Phenyl salicylate

　　Properties and Uses: Colorless crystalline powder. It has a pleasant aromatic odor (wintergreen oil odor). Density 1.250 g/cm3, melting point 43℃, boiling point (1.6 kPa) 173℃. It is easily soluble in ether, benzene, and chloroform, soluble in ethanol, and almost insoluble in water and glycerin.

　　This product is a UV absorber used in plastic products, but its absorption wavelength range is relatively narrow. It is approved by the U.S. Food and Drug Administration for use in acrylic resin products that come into contact with food.

　 　No.2

　　UV absorber UV-P

　　Component: Reaction product of o-nitroaniline and p-cresol

　　Properties and Uses: Appearance is colorless or light yellow crystals. It is soluble in gasoline, benzene, acetone, and many other organic solvents. It has very low solubility in water and is not decomposed by strong alkalis or strong acids. It can react with heavy metal ions to form salts. It can absorb ultraviolet light with a wavelength of 270～280 nm. Melting point 130～131℃.

　　This product is mainly used in polyester, chlorinated polyester, acetate fiber, polyvinyl chloride, polystyrene, organic glass, polyacrylonitrile, and other resins. Its stability in transparent products is better than in colored products. The dosage in products is 0.1%～0.5%.

　 　No.3

　　UV absorber UV-O

　　Component: 2,4-Dihydroxybenzophenone

　　Properties and Uses: This product is a light-colored needle-like crystal or white powder. Moisture <0.5%. Ash <0.5%. Melting point 136～149℃. Soluble in acetone, methanol, ethanol, methyl ethyl ketone, dioxane, N-methylpyrrolidone, and ethyl acetate, very difficult to dissolve in water, n-heptane, and benzene. The solubility of this product in some solvents (g/100 ml solvent, 25℃) is acetone 50, benzene 1, ethanol >50, water <0.5, n-heptane <0.5.

　　This product is a UV absorber suitable for polyvinyl chloride, polystyrene, epoxy resin, cellulose resin, unsaturated polyester, coatings, and synthetic rubber. The maximum absorption wavelength range is 280～340 nm, and the general dosage is 0.1%~1%. However, its light stabilization effect is not outstanding.

　　No.4

　　UV absorber UV-9

　　Component: 2-Hydroxy-4-methoxybenzophenone

　　Properties and Uses: This product is a light yellow or white crystalline powder. Density 1.324 g/cm3. Melting point 62～66℃. Boiling point 150～160℃ (0.67 kPa), 220℃ (2.4 kPa). Soluble in acetone, ketone, benzene, methanol, ethyl acetate, methyl ethyl ketone, and ethanol, and most organic solvents, insoluble in water. The solubility of this product in some solvents (g/100 g solvent, 25℃) is benzene 56.2, n-hexane 4.3, ethanol (95%) 5.8, carbon tetrachloride 34.5, styrene 51.2, DOP 18.7.

　　This product is a UV absorber suitable for polyvinyl chloride, polyvinylidene chloride, polymethyl methacrylate, unsaturated polyester, ABS resin, and cellulose resin, and many other plastics. The maximum absorption wavelength range is 280～340 nm, and the general dosage is 0.1%～1.5%. It has good thermal stability and does not decompose at 200℃. This product absorbs almost no visible light, so it is suitable for light-colored transparent products. This product can also be used in paints and synthetic rubber.

　　Safety Precautions: Japan and Italy stipulate that when this product is used in products that come into contact with food, the maximum dosage should not exceed 0.3%.

　　No.5

　　UV absorber UV-531

　　Component: 2-Hydroxy-4-n-octyloxybenzophenone

　　Properties and Uses: This product is a light yellow or white crystalline powder. Density 1.160 g/cm3 (25℃). Melting point 48～49℃. Soluble in acetone, benzene, ethanol, isopropanol, slightly soluble in dichloroethane, insoluble in water. The solubility of this product in some solvents (g/100 solvent, 25℃) is acetone 74, benzene 72, methanol 2, ethanol (95%) 2.6, n-heptane 40, n-hexane 40.1, water 0.5.

　　This product is an ultraviolet absorber that strongly absorbs ultraviolet light with a wavelength of 270-330 nm. It can be used in various plastics, especially polyethylene, polypropylene, polystyrene, ABS resin, polycarbonate, and polyvinyl chloride. It has good compatibility with resins and low volatility. The general dosage is 0.1% to 1%. Synergistic effects are observed when used with a small amount of 4,4'-thiobis(6-tert-butyl-m-cresol). This product can also be used as a light stabilizer for various coatings.

　　Safety Precautions: This product has low toxicity, and many countries permit its use in plasticized products that come into contact with food. For example, the United States allows its use in polyolefins, the United Kingdom has a maximum dosage of 0.6%, Italy has a maximum dosage of 0.5% for polyethylene and polypropylene, and Japan's dosage is 0.5% for polyethylene, 1% for polypropylene, 0.5% for AS resin and ABS resin, and 0.2% for polyvinyl chloride (cannot contact oily foods or foods with an ethanol content exceeding 20%).

　　No.6

　　UV Absorber UVP-327

　　Component: 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole

　　Performance and Applications: This product is a UV absorber. Its characteristics and applications are similar to UV-326. It strongly absorbs ultraviolet light with a wavelength of 270-380 nm. It has good chemical stability and extremely low volatility. It has good compatibility with polyolefins, especially suitable for polyethylene and polypropylene. In addition, it can also be used in polyvinyl chloride, polymethyl methacrylate, polyformaldehyde, polyurethane, unsaturated polyester, ABS resin, epoxy resin, and cellulose resin, etc. This product has excellent heat sublimation resistance, washability, gas fading resistance, and mechanical property retention. Synergistic effects are observed when used with antioxidants to improve the thermo-oxidative stability of the product. The general dosage in plastics is 1% to 3%.

　　Safety Precautions: This product has low toxicity. Japan, the United States, France, and Italy permit its use in polyolefin plastics that come into contact with food, with a maximum dosage of 0.5%. For other plastics that come into contact with food, Italy stipulates a maximum dosage of 0.2%, while Japan and France stipulate 0.5%.

　　No.7

　　UV Absorber RMB

　　Component: Resorcinol monobenzoate

　　Performance and Applications: This product is a white crystalline powder. Melting point 132-135℃, boiling point 140℃ (20Pa). Bulk density 0.68g/cm3(20%). Soluble in acetone and ethanol, slightly soluble in benzene, water, n-heptane, etc.

　　This product is a UV stabilizer, its effectiveness is similar to benzophenone-type stabilizers. It is mainly used in polyvinyl chloride, cellulose resin, polystyrene, the general dosage is 1% to 2%.

　　No.8

　　Light Stabilizer AM-101

　　Component: 2,2'-Thiobis(4-octylphenoxy)nickel

　　Performance and Applications: This product is a green powder. The absorption peak in the ultraviolet region is 290 nm (in chloroform). It is suitable for polyolefin plastics such as polyethylene and polypropylene. It is particularly effective for the light stabilization of films and fiber products and can improve processing performance. This product has a good synergistic effect when used with UV absorbers, further improving light stabilization performance. Its main drawbacks are its darker color, which causes the product to be colored, and at high temperatures, it reacts with thioester-type auxiliary antioxidants, causing the product to turn grayish-black.

　　Safety Precautions: This product is toxic and should be used with caution.

　　No.9

　　Light Stabilizer GW-540

　　Component: Tris(1,2,2,6,6-pentamethylpiperidyl) phosphite

　　Performance and Applications: This product is a white crystalline powder. Melting point 122-124℃. Soluble in ethanol, chloroform, acetone, benzene, etc., insoluble in water.

　　This product is a hindered light stabilizer. It does not absorb ultraviolet light itself, but it can capture active free radicals produced by polymer degradation, decompose hydroperoxides, and transfer the energy of excited state molecules, etc. Its light stabilization effect is 24 times that of general UV absorbers. This product is suitable for polyethylene, polypropylene, etc. It has good compatibility with resins and good processing performance, and it is also low in toxicity. In addition to its light stabilization effect, it also has good anti-thermo-oxidative aging performance. However, this product has poor heat resistance and should not be used in hot water media for a long time. In addition, this product is best processed and used at temperatures below 270℃; above this temperature, weight loss is more serious.

　 　No.10

　　Light Stabilizer 744

　　Component: 4-Benzoyloxy-2,2,6,6-tetramethylpiperidine

　　Performance and Applications: This product is a white crystalline powder. Melting point 95-98℃, decomposition temperature above 280℃. Soluble in acetone, ethanol, ethyl acetate, toluene, insoluble in water.

　　This product is a hindered light stabilizer. It hardly absorbs ultraviolet light itself, but it can effectively capture the active free radicals generated by the action of ultraviolet light on high molecular materials, thus exerting a light stabilization effect. This product is suitable for various plastics such as polypropylene, polyethylene, polystyrene, polyurethane, polyamide, and polyester, and its effect is particularly prominent in polyolefins. The light resistance of this product is several times that of general UV absorbers. It is non-coloring, non-polluting, has good heat resistance and processability, and has excellent synergistic effects when used with antioxidants and UV absorbers.

　　No.11

　　Triazine UV Absorber

　　Component: 2,4,6-Tris(2'-n-butoxyphenyl)-1,3,5-triazine

　　Performance and Applications: This product is a light yellow powder. Melting point 156-165℃. Soluble in hexamethylphosphoramide, soluble in dimethylformamide when heated, slightly soluble in n-butanol, insoluble in water.

　　This product is an ultraviolet absorber that absorbs ultraviolet light with a wavelength of 300～380nm. It is suitable for various plastics such as polyvinyl chloride, polyformaldehyde, and chlorinated polyether. The dosage is generally no more than 1%. Its light stabilization performance is superior to UV-9 and UV-531, but this product has coloring properties, which can make the product slightly yellow, and its compatibility with resins is also poor.

　　No.12

　　Light Stabilizer HPT

　　Component: Hexamethylphosphoramide

　　Properties and Uses: This product is a colorless or light yellow transparent liquid with a slightly pungent and astringent odor. Density 1.0253～1.0257g/cm3 (20℃), freezing point 27℃, boiling point 116～117℃ (1.48kPa), refractive index 1.4582～1.4589 (20℃). It is soluble in polar and non-polar solvents and is miscible with commonly used plasticizers such as dioctyl phthalate, dioctyl sebacate, and triphenyl phosphite in any proportion.

　　This product can be used as a polyvinyl chloride light stabilizer. It can provide the product with excellent outdoor anti-aging performance, hence it is known as a high-efficiency weather-resistant agent for polyvinyl chloride. Adding 2～5 parts of this product to polyvinyl chloride film can not only significantly improve its weather resistance and cold resistance, but also reduce the processing temperature by about 10℃. In addition, this product can also be used as an excellent solvent for various polymer materials such as polyamide, polyurethane, urea-formaldehyde resin, and polyphenylene sulfide.