Improve material weather resistance: Are you familiar with UV absorber standards?

Improve material weather resistance: Are you familiar with UV absorber standards?

Coatings Industry：

  Ⅰ. Terms and Definitions

Sunlight contains a large amount of harmful ultraviolet rays with wavelengths ranging from 290 to 460 nm, which can cause discoloration of colored materials. These harmful UV rays trigger chemical redox reactions and eventually break down color molecules, leading to fading. The application of UV absorbers can effectively prevent or mitigate the damage caused by ultraviolet radiation to protected substrates.

UV absorbers are a type of light stabilizer. They can absorb ultraviolet rays from sunlight and fluorescent light without undergoing any chemical changes themselves.

When exposed to sunlight and fluorescent light, plastics and other polymer materials undergo auto-oxidation triggered by UV radiation. This causes polymer degradation and deterioration, resulting in impaired appearance and mechanical properties.

Incorporating UV absorbers enables the materials to selectively absorb high-energy ultraviolet rays, converting them into harmless energy for release or dissipation. Since polymers degrade under UV rays of different wavelengths depending on their type, various UV absorbers target specific wavelength ranges. Therefore, UV absorbers shall be selected according to the type of polymer in use.

  II.Relevant Standards

• HG/T 5084-2016(2023)UV Absorber — 2-Hydroxy-4-n-octyloxybenzophenone (UV-531)
• SN/T 5258-2020 Determination of UV-320 and UV-328 UV absorbers in coatings — High performance liquid chromatography
• SN/T 5259-2020 Determination of UV-320, UV-327, UV-328 and UV-350 UV absorbers in coatings — Gas chromatography-mass spectrometry

  III. Classification and Functions of UV Absorbers

UV absorbers shall meet the following requirements:

• Capable of strongly absorbing ultraviolet rays, especially those with a wavelength ranging from 290 to 400 nm;
• Excellent thermal stability with low thermal volatility, and no deterioration during material processing;
• Good chemical stability, and no adverse reactions with other components in finished products;
• High compatibility for uniform dispersion in materials, without blooming or exudation;
• Superior photochemical stability of the absorber itself, free from decomposition and discoloration;
• Colorless, non-toxic and odorless;
• Good resistance to washing and leaching;
• Economical and easily available.

Benzotriazole UV absorbers are widely used domestically at present. However, triazine UV absorbers deliver remarkably better performance.

Triazine absorbers feature excellent UV absorption capacity along with multiple advantages. They are widely applicable to polymers, and possess good thermal stability, processing stability and acid resistance. In practical use, triazine UV absorbers work excellently in synergy with hindered amine light stabilizers (HALS). Combined application achieves superior results compared with separate use.

   IV.Several Common UV Absorbers

(1) Reaction product of o-nitroaniline and p-cresol

Appearance: Colorless or pale yellow crystals. Soluble in gasoline, benzene, acetone and other organic solvents, while barely soluble in water. It is not decomposed by concentrated alkalis or concentrated acids, and can form salts with heavy metal ions. It absorbs ultraviolet light at wavelengths of 270–280 nm. Melting point: 130–131 °C.

It is mainly applied to resins such as polyester, chlorinated polyester, cellulose acetate, PVC, polystyrene, polymethyl methacrylate and polyacrylonitrile. It performs better in transparent products than in colored ones. The recommended dosage in finished products is no more than 0.5%.

(2) 2-Hydroxy-4-methoxybenzophenone (UV-9)

Pale yellow or white crystalline powder. Density: 1.324 g/cm³. Melting point: 62–66 °C. Boiling point: 150–160 °C (0.67 kPa), 220 °C (2.4 kPa).

Soluble in most organic solvents including acetone, benzene, methanol, ethyl acetate, methyl ethyl ketone and ethanol, but insoluble in water. Solubility in selected solvents (g/100 g solvent, 25 °C): benzene 56.2, n-hexane 4.3, 95% ethanol 5.8, carbon tetrachloride 34.5, styrene 51.2, DOP 18.7.

As a UV absorber, it is suitable for various plastics such as PVC, polyvinylidene chloride, polymethyl methacrylate, unsaturated polyester, ABS resin and cellulose resin. Its maximum UV absorption wavelength ranges from 280 to 340 nm. The typical dosage is 0.1%–1.5%. It features excellent thermal stability and does not decompose at 200 °C. Hardly absorbing visible light, it is ideal for pale and transparent products. It can also be used in paints and synthetic rubber.

(3) 2-Hydroxy-4-n-octyloxybenzophenone (UV-531)

Pale yellow or white crystalline powder. Density: 1.160 g/cm³ (25 °C). Melting point: 48–49 °C. It is soluble in acetone, benzene, ethanol and isopropanol, slightly soluble in dichloroethane, and insoluble in water.

Solubility in selected solvents (g/100 g solvent, 25 °C): acetone 74, benzene 72, methanol 2, 95% ethanol 2.6, n-heptane 40, n-hexane 40.1, water 0.5.

As a UV absorber, it strongly absorbs ultraviolet light at wavelengths of 270–330 nm. It is applicable to a wide range of plastics, especially polyethylene, polypropylene, polystyrene, ABS resin, polycarbonate and PVC. It features good compatibility with resins and low volatility. The typical dosage is 0.1%–1%. It shows an excellent synergistic effect when used together with a small amount of 4,4'-thiobis(6-tert-butyl-p-cresol). This product can also serve as a light stabilizer for various coatings.

(4)2-(2'-Hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole (UV-327)

As a UV absorber, it has similar properties and applications to benzotriazole UV-326. It strongly absorbs ultraviolet light at wavelengths of 270–380 nm, featuring good chemical stability and extremely low volatility. It exhibits excellent compatibility with polyolefins, and is particularly suitable for polyethylene and polypropylene.

It can also be used in PVC, polymethyl methacrylate, polyoxymethylene, polyurethane, unsaturated polyester, ABS resin, epoxy resin and cellulose resin. This product boasts outstanding resistance to thermal sublimation, washing resistance, gas fading resistance and good retention of mechanical properties. It delivers a remarkable synergistic effect when combined with antioxidants, effectively improving the thermal-oxidative stability of finished products.

(5) Resorcinol monobenzoate

White crystalline powder. Melting point: 132–135 °C. Bulk density: 0.68 g/cm³ (20%). Soluble in acetone and ethanol, slightly soluble in benzene, water, n-heptane and other solvents.

As a UV light stabilizer, it has performance similar to benzophenone-type light stabilizers. It is mainly used in PVC, cellulose resins and polystyrene, with a typical dosage of 1%–2%.

Want to know more? Please contactus at: yihoo@yihoopolymer.com. Besides the aforementioned high-performance nylon materials, we also offer various chemicalproducts such as light stabilizers, UVabsorbers, antioxidants, WPC-specific additives, nucleating agents, anti-static agents, matte polyurethane dispersions, etc. Welook forward to your inquiries!