UV absorber
Ultraviolet absorbers are a type of substance that can prevent polymer degradation caused by sunlight or other artificial ultraviolet light. They are a kind of light stabilizer. Since sunlight contains a large amount of ultraviolet light that is harmful to colored objects, its wavelength is about 290-460nm. These harmful ultraviolet light causes the color molecules to eventually decompose and fade through chemical oxidation and reduction, and the use of ultraviolet absorbers can protect the protected objects. Objects can be implemented to effectively prevent or weaken the damage to color. After adding ultraviolet absorbers, this high-energy ultraviolet ray can be selectively absorbed and turned into harmless energy for release or consumption. Due to different types of polymers, the wavelengths of ultraviolet rays that cause degradation are also different. Different ultraviolet absorbers can absorb ultraviolet rays of different wavelengths. When used, ultraviolet absorbers should be selected according to the type of polymer.
Mechanism of UV absorbers
1. The reason why ultraviolet absorbers can absorb ultraviolet light is that the molecules of this type of compounds contain two parts: a structure of a conjugated π electron system and a structure that can move hydrogen atoms. Some only have the first part.
2. The structural molecule of ultraviolet absorbers contains at least one ortho-hydroxyphenyl substituent. In this type of compound, a chelate ring is formed by ortho-hydroxyl groups and nitrogen atoms or oxygen atoms. After absorbing ultraviolet rays, hydrogen bonds Molecular isomerism occurs when fracture occurs, thermal vibration occurs in the intramolecular structure, hydrogen bonds are destroyed, chelate rings open, and the intramolecular structure changes, thus converting harmful ultraviolet light into harmless heat energy and releasing it, thus protecting the material.
3. In this process, the chelate ring formed in the molecule is the key to its ability to absorb ultraviolet light. The energy sensitive range of opening this ring is exactly the ultraviolet energy range of 290~nm wavelength.
4. In addition, as an ultraviolet absorber, it must be able to prevent photochemical reactions under the action of ultraviolet light or visible light; have good stability to chemicals and water, and good stability to heat; have low volatility; and be resistant to high temperatures. Molecular materials have good compatibility and are not extracted by solvents.
Conditions that UV absorbers should meet
1. Can strongly absorb ultraviolet rays (especially the wavelength of 290-nm);
2. Good thermal stability, will not change due to heat even during processing, and has low thermal volatility;
3. Good chemical stability and no adverse reactions with material components in the product;
4. Good miscibility, can be evenly dispersed in the material, no blooming, no bleeding;
5. The absorber itself has good photochemical stability and does not decompose or discolor;
6. Colorless, non-toxic and odorless;
7. Resistant to soaking and washing;
8. Cheap and easy to obtain;
9. Insoluble or difficult to dissolve in water.
Classification of UV absorbers
According to chemical structure, UV absorbers can be divided into salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, triazines and hindered amines.
Benzotriazoles
This type of compound is the product with the largest output and the most varieties among ultraviolet absorbers, and research at home and abroad is also very active. The synthesis of benzotriazole ultraviolet absorbers is generally made by diazotizing aromatic amines to form diazonium salts. The diazonium salts undergo a coupling reaction with phenolic compounds to form intermediate azo pigments, which are then ring-closed through reduction.
Benzophenones
The output and variety of this type of UV absorber is second only to benzotriazole.
The synthesis route is basically a two-step reaction, namely the synthesis of 2,4-dihydroxybenzophenones and the synthesis of alkoxybenzophenones.
Research direction of ultraviolet absorbers
1. High molecular weight
Reduce the volatility of additives and reduce losses during the reaction
2. Multifunctionality
Make a stabilizer molecule have groups with different functions at the same time, playing a variety of stabilizing effects (thermal stabilizer, antioxidant…)
3. Reactivity
The reactive group is introduced into the light stabilizer molecule so that it can bond with the base polymer during processing, thus permanently existing in the polymer original hot melt adhesive material imported from Germany
Applications of UV absorbers��
1. Due to different types of polymers, the wavelengths of ultraviolet rays that cause degradation are also different. Different ultraviolet absorbers can absorb ultraviolet rays of different wavelengths. When used, ultraviolet absorbers should be selected according to the type of polymer.
2. Ultraviolet absorbers used in cosmetics can reduce or completely absorb ultraviolet rays and protect the skin. However, excessive use or use of prohibited ultraviolet absorbers can cause irritation to the skin and cause skin allergies.
Phenyl salicylate
Ingredients: phenyl o-hydroxybenzoate
Performance and use: colorless crystalline powder. Has a pleasant aromatic smell (wintergreen oil smell). Density 1.250g/cm3, melting point 43, boiling point (1.6kP Cabot White Carbon Black a) 173. Easily soluble in ether, benzene and chloroform, soluble in ethanol, almost insoluble in water and glycerin. Content 99%.
This product is a UV absorber used in plastic products, but its absorption wavelength range is narrow. The U.S. Food and Drug Administration approves acrylic resin articles for use in contact with food.
Ciba Chimassorb 81
Chimassorb 81 is a benzophenone UV absorber that can provide good light stabilization protection when used in combination with hindered amine light stabilizers. Good compatibility with polyolefins and soft PVC.
Application: Chimassorb 81 is used in combination with hindered amines. It is mainly used in low-density agricultural films, linear low-density polyethylene and EVA copolymers. It can also be used as a UV screener to protect the contents of industrial/civilian packaging. In addition, when combined with hindered amine light stabilizer, it can be used in high-density polyethylene molded products, such as turnover boxes. Chimassorb 81 can also provide light stabilizing protection for other polymers, such as soft PVC and rubber; Chimassorb 81 can be used in combination with antioxidants, phosphites, and other light stabilizers.
Function: Chimassorb 81 is particularly suitable for thicker films (>100µm) and thick parts. It has low saturated vapor pressure and little loss during processing. The migration rate is low and it is not easy to bloom.
UV absorber BP-2
Chemical name: 2,2′,4,4′-Tetrahydroxybenzophenone
Molecular formula: C13H10O5
Usage: The absorption wavelength range is 320-nm. It has a symmetrical benzene ring and hydroxyl groups on both sides. Its thermophotochemical properties are stable and superior to BP-1. It is an anti-UV additive for oily cosmetics and is currently widely used. Among polyester, coatings and cosmetics, its application on fabrics has attracted attention from the textile industry in recent years, and its scope has become wider and wider.
Total Summary
1. Ultraviolet absorbers are an important category of plastic additives. In order to meet the needs of industrial development, the development trend in this field is towards high molecular weight, reactive, and multi-functional development. As a result It is environmentally friendly and highly efficient. This is the inevitable result of the sustainable development of the polymer material additive industry.
2. There is a big gap between the domestic additive industry and foreign countries. The main problems are few varieties, low output, high cost, unmatched raw material supply, poor cooperation with the plastic processing industry, and lack of technical communication. It is recommended to strengthen technological transformation, improve product quality and improve economic benefits.
