Language
- Chinese

language

Tel

Tel

+8618142863185
Follow us

Official Accounts

Official Accounts
Top

News

Introduction to UV Absorbers and Their Applications

Release time:

2016-03-25 10:46

Introduction to UV Absorbers and Their Applications

I. What are UV Absorbers?

1. UV absorbers are a class of substances that can prevent the degradation of polymers caused by sunlight or other artificial ultraviolet light; they are a type of light stabilizer.

2. Since sunlight contains a large amount of ultraviolet light, which is harmful to colored objects and has a wavelength ranging from approximately 290 to 460 nm, this harmful ultraviolet light causes color molecules to eventually decompose and fade through chemical redox reactions. By using UV absorbers, we can effectively prevent or mitigate the damaging effects of ultraviolet radiation on protected objects.

3. After the addition of a UV absorber, this high-energy ultraviolet radiation can be selectively absorbed and converted into harmless energy that is either released or consumed. Since different types of polymers have varying susceptibility to degradation by ultraviolet radiation, the wavelengths of UV radiation that cause degradation also differ among polymers. Consequently, different UV absorbers are capable of absorbing different UV wavelengths. When selecting a UV absorber, it is essential to take into account the specific type of polymer involved.

II. Mechanism of Ultraviolet Absorbers

1. The reason why UV absorbers can absorb ultraviolet light is that these compounds contain two structural components: a conjugated π-electron system and a structure capable of hydrogen atom migration. Some UV absorbers, however, possess only the former component.

2. UV absorbers contain at least one ortho-hydroxyphenyl substituent in their molecular structure. In these compounds, the ortho-hydroxy group forms a chelate ring with either a nitrogen or oxygen atom. After absorbing ultraviolet radiation, the hydrogen bonds within the chelate ring break, leading to molecular isomerization and thermal vibration of the intramolecular structure. As the hydrogen bonds are disrupted and the chelate ring opens, the molecular structure undergoes significant changes. In this way, harmful ultraviolet light is converted into harmless thermal energy and released, thereby protecting the material.

3. In this process, the chelate ring formed within the molecule is key to its ability to absorb ultraviolet light; the energy-sensitive range required to open this ring precisely corresponds to the ultraviolet wavelength range of 290–400 nm.

4. Additionally, as a UV absorber, it must also remain chemically stable under the influence of ultraviolet or visible light without undergoing photochemical reactions; exhibit good chemical and water stability, as well as excellent thermal stability; have low volatility; demonstrate good compatibility with polymeric materials and not be extracted by solvents.

III. Requirements for UV Absorbers

1. It can strongly absorb ultraviolet radiation (especially wavelengths between 290 and 400 nm);

2. Good thermal stability—remains unchanged even during processing and exhibits low thermal volatility.

3. Good chemical stability, with no adverse reactions occurring with the material components in the product.

4. Excellent miscibility—can be uniformly dispersed throughout the material without blooming or exudation.

5. The absorbent itself has good photochemical stability, does not decompose, and does not change color.

6. Colorless, non-toxic, and odorless;

7. Resistant to soaking and washing;

8. Inexpensive and readily available;

9. Insoluble, or poorly soluble in water.

IV. Classification of UV Absorbers

According to their chemical structure, UV absorbers can be classified into salicylate esters, benzophenones, benzotriazoles, substituted acrylonitriles, triazines, and hindered amine compounds.

1. Benzotriazole class

This class of compounds represents the largest in terms of production volume and the most diverse in terms of variety among UV absorbers, and research both domestically and internationally in this field is highly active. The synthesis of benzotriazole UV absorbers typically involves the diazotization of aromatic amines to form diazonium salts, which then undergo coupling reactions with phenolic compounds to generate intermediate azo pigments, followed by reduction and cyclization to complete the synthesis.

2. Benzophenones

The production volume and variety of this type of UV absorber rank second only to benzotriazoles.

Its synthetic route essentially involves two-step reactions: the synthesis of 2,4-dihydroxydiphenone and the synthesis of alkoxydiphenone.

V. Research Directions on Ultraviolet Absorbers

1. High molecular weightization

Reduce the volatility of additives and minimize losses during the reaction process.

2. Multifunctionality

Enable a stabilizer molecule to simultaneously possess functional groups with different roles, thereby achieving multiple stabilizing effects (e.g., thermal stabilizers, antioxidants, etc.).

3. Reactivity enhancement

Introduce reactive functional groups into the photostabilizer molecules so that they can bond with the base polymer during processing, thereby ensuring their permanent presence in the polymeric material.

VI. Application Examples of UV Absorbers

1. Since different types of polymers have varying degrees of degradation under ultraviolet radiation, the wavelengths of UV light that cause their degradation also differ. Different UV absorbers can absorb different wavelengths of UV light; therefore, when selecting a UV absorber, it is essential to take into account the type of polymer involved.

2. UV absorbers used in cosmetics can reduce or completely absorb ultraviolet radiation, thereby protecting the skin. However, if used in excessive amounts or with prohibited UV absorbers, they may irritate the skin and trigger allergic reactions.

3. Salicylic acid phenyl ester

Ingredient: Benzyl p-hydroxybenzoate

Properties and Applications: Colorless crystalline powder with a pleasant aromatic odor (reminiscent of wintergreen oil). Density: 1.250 g/cm³; Melting point: 43°C; Boiling point (at 1.6 kPa): 173°C. Easily soluble in ether, benzene, and chloroform; soluble in ethanol; almost insoluble in water and glycerol. Purity: 99%.

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

4. Ciba Chimassorb 81

Chimassorb 81 is a benzophenone-based UV absorber that, when used in combination with hindered amine light stabilizers, provides excellent photostabilization protection. It exhibits good compatibility with polyolefins and soft PVC.

Chemical name: 2-Hydroxy-4-octyloxybenzophenone

Chemical structure:

Application: Chimassorb 81, when used in combination with hindered amine light stabilizers, is primarily applied in agricultural films made from low-density, linear low-density polyethylene, and EVA copolymers. It can also serve as a UV shield, protecting the contents of industrial and consumer packaging. Additionally, when combined with hindered amine light stabilizers, it is suitable for molding products made from high-density polyethylene, such as周转 boxes. Chimassorb 81 can also provide photostabilization protection for other polymers, including soft PVC and rubber. Chimassorb 81 can be formulated in combination with antioxidants, phosphites, and other light stabilizers.

Features: Chimassorb 81 is particularly well-suited for thicker films (>100 µm) and thick molded parts. It has a low saturation vapor pressure, resulting in minimal loss during processing. It exhibits low migration and is less likely to cause blooming.

5. UV Absorber UV-P

Chemical name: 2-(2′-hydroxy-5′-methylphenyl)benzotriazole

Molecular formula: C13H11N3O

Molecular weight: 225.3

Chemical structural formula:

Applications: As a UV absorber, this product is primarily suitable for polyester, epoxy cellulose acetate, polyvinyl chloride, polystyrene, acrylic glass, polyacrylonitrile resin, and other materials. Its maximum absorption wavelength range is 270–380 nm. Typical usage levels are: 0.1–0.5% for thin products and 0.05–0.2% for thick products.

UV Absorber BP-2

Chemical name: 2,2',4,4'-Tetrahydroxybenzophenone

Molecular formula: C13H10O5

Applications: Absorbs wavelengths in the range of 320–400 nm, features a symmetrical benzene ring with hydroxyl groups on both sides, and exhibits stable thermo-photchemical properties—superior to those of BP-1. It serves as an ultraviolet-resistant additive for oily cosmetics and is currently widely used in polyester, coatings, and cosmetics. In recent years, its application on textiles has gained increasing attention from the textile industry, and its scope of use continues to expand.

VII. Summary

1. UV absorbers are a major and important category of plastic additives. To meet the demands of industrial development, this field is trending toward higher molecular weights, reactive formulations, and multifunctionality—resulting in greater environmental friendliness and enhanced performance. This represents an inevitable outcome of the sustainable development of the polymer materials additives industry.

2. Compared with foreign countries, China’s additive industry still has a significant gap. The main issues include a limited variety of additives, low production volumes, high costs, inadequate supply of raw materials, insufficient coordination with the plastics processing industry, and a lack of effective technical communication. It is recommended to intensify technological upgrades, improve product quality, and enhance economic efficiency.

Share to:

Detailed Explanation of Ceramic Decal Application Technique

Introduction to Wood UV Coatings and Their Applications