Anti-UV finishing of textiles
2016-07-18 College of Fashion Technology, Shanghai University of Engineering and Technology Qian Rushan Zhu Chuanlong et al
Abstract: From the influence of the fiber type and structure of the fabric on the UV resistance of the fabric, the mechanism of ozone layer destruction by chlorofluorocarbons and the damage to the human body are reviewed. After a comprehensive analysis of the current shortcomings in anti-UV finishing of fabrics, it is proposed that nano-anti-UV is the research direction of anti-UV finishing.
Keywords: Ozone fabric anti-UV finishing agent
1Introduction
Since German physicist Ritter discovered ultraviolet light in 1801, people have been understanding and studying ultraviolet light for more than two centuries. Ultraviolet rays are an electromagnetic ray from solar radiation. The International Commission on Illumination (CIE) divides the ultraviolet spectrum into three different bands. According to the ultraviolet wavelength, it can be divided into: near ultraviolet LNA (315-400nm), far ultraviolet UVB (280-315nm) and ultraviolet Short UV LNC (100-280). Electromagnetic waves with wavelengths below 300nm in sunlight are almost absorbed by ozone in the atmosphere and hardly reach the ground. Therefore, most of the radiation that reaches the ground is near ultraviolet and far ultraviolet. Appropriate exposure to ultraviolet rays is good for the body. It helps the body absorb calcium, strengthens the body’s non-specific immune function and defense capabilities, and promotes the secretion of certain hormones in the body. However, excessive exposure to ultraviolet rays can cause physical discomfort and even lead to many diseases. A large number of animal experiments have shown that UV-B ultraviolet radiation can damage the cornea and lens, causing eye opacity. Some studies have also shown that ultraviolet radiation can disrupt the human body’s immune system (such as causing people to produce melanin), suppress immunity, and worsen or increase diseases such as tuberculosis and herpes simplex.
Excessive UV rays can cause severe damage to skin in particular. The shorter the wavelength of ultraviolet rays, the more harmful it is to human skin. Short-wave UV rays can pass through the dermis, while medium-wave UV rays can enter the dermis. Excessive ultraviolet rays can damage the DNA in skin cells, causing sun spots and pigmentation. If the DNA damage of epidermal cells increases and exceeds its repair capacity, it can cause skin cancer.
In recent years, as people’s requirements for living standards have become higher and higher, while enjoying comfort, a large amount of fluorine and chlorine compounds have been emitted into the atmosphere, causing increasingly serious damage to the ozone layer. The amount of ultraviolet radiation reaching the ground increases, and the damage to the human body becomes more and more serious. Therefore, research on human body protection from ultraviolet radiation has received attention, and clothing is an effective protection tool for the human body. Therefore, it is necessary to carry out anti-ultraviolet finishing on textiles. Preventing ultraviolet rays from damaging the skin while maintaining the original properties of the fabric has become a key issue in the textile dyeing and finishing industry. One of the important topics.
2 Anti-UV finishing of fabrics
2.1 Factors affecting the transmission of ultraviolet rays through fabrics
Fabrics without anti-UV finishing have certain UV protection effects. The UV protection effect is related to the type, shape structure, structure and thickness of the fabric. It is generally believed that fibers containing benzene rings and aromatic amino acids in their molecular structures (such as polyester, wool, silk, etc.) have strong absorption of ultraviolet light below 300 nm and low ultraviolet transmittance; fibers with a smooth cylindrical shape are The light reflectivity is high; the fabric structure has fewer interweaving points and a longer floating length (such as satin weave), which has better anti-UV radiation effect; thicker fabrics have less UV transmittance.
The structure of cotton fiber does not contain benzene rings and has a longitudinally twisted and matte shape. Ultraviolet rays can easily penetrate cotton fabrics, so anti-UV finishing of cotton fabrics is particularly important.
2.2 Classification of anti-UV finishing agents
The research on anti-UV finishing agents has attracted people’s attention very early. According to the anti-UV mechanism, it can be divided into: reflective anti-UV finishing agents, absorption-type anti-UV finishing agents and nano-type anti-UV finishing agents.
2.2.1 Reflective anti-UV finishing agent
Reflective anti-UV finishing agents have no absorption effect on ultraviolet rays, but rely on the reflection of light to reduce the transmittance of ultraviolet rays. Also known as UV screener. This type of shielding agent is non-toxic, odorless, non-irritating, has good thermal stability, does not decompose and is non-volatile. Most of them are metals, metal oxides and salts, typically such as Ti02, Zn0, Al02, kaolin, and talc. Powder, carbon black, iron oxide, lead oxide and CaC03, etc., the reflectivity of ultraviolet light with a wavelength of 310-400nm can be as high as 95%.
Although UV shielding agents have unique advantages, the breathability, hand feel and washability of the fabrics after treatment are poor, and the color, fastness and whiteness of the fabrics are reduced, and some even cause allergic reactions in the human body. Therefore, this type of finishing agent is mostly used in parasols, tents, etc., but is rarely used in clothing fabrics.
2.2.2 Absorbent anti-UV finishing agent
Absorbent anti-UV finishing agents, also known as UV absorbers, can strongly and selectively absorb high-energy UV rays and release them in other lower-energy forms (such as longer wavelength light or heat), thereby avoiding the effects of UV rays on Damage to human skin, while the absorber itself is not damaged by ultraviolet rays. The principle of its absorbent is generally considered to be divided intoIntra-proton transfer: The hydroxyl group in the structure forms an intramolecular six-membered ring containing hydrogen bonds with the N or O atoms in the nearby structure. The six-membered ring opens after absorbing energy under ultraviolet irradiation, accompanied by the enol and keto structures. The conversion of harmful energy into harmless light waves or heat energy release, the six-membered ring then closes and recovers.
As a UV absorber for fabrics, it should meet the following conditions:
(1) Safe and non-toxic, no allergic reaction to the human body, and no threat to human health;
(2) Meet environmental protection requirements;
(3) Good resistance to commonly used solvents and washing resistance;
(4) There is no coloring after absorbing ultraviolet rays;
(5) No or little impact on the physical properties and fabric style such as whiteness, fastness, strength and feel of the fabric;
(6) It has certain stability.
Common UV absorbers are:
① Benzophenone compounds:
It is the earliest UV absorber used. The carbonyl group and hydroxyl group in the molecule of this type of compound form intramolecular hydrogen bonds to form a chelate ring structure. After absorbing ultraviolet light, the internal hydrogen bonds oscillate, the stable chelate ring opens, and the absorbed energy is released in the form of heat energy. In addition, the carbonyl group in the molecule will be excited by the absorbed ultraviolet light energy to form an enol structure. Tautomerism, which also consumes some energy.
Such compounds include: 2-hydroxy. 5 chlorobenzophenone, 2-4 dihydroxybenzophenone, etc. This type of compound has multiple hydroxyl groups, has good adsorption capacity for fibers, and can absorb ultraviolet light from 280 to 400 nm. It is mainly used in polypropylene, polyester, cellulose and other fibers. However, it has almost no absorption of ultraviolet light below 280nm, and sometimes tends to turn yellow. In addition, it is relatively expensive, so it is rarely used in the market.
② Salicylates:
There are also internal hydrogen bonds in the molecules of salicylate UV absorbers. At the beginning, the UV absorption capacity is low and the absorption range is narrow (less than 340nm). However, after irradiation for a certain period of time, the absorption gradually increases. The reason is that molecular rearrangement occurs under ultraviolet irradiation to form a benzophenone structure with strong ultraviolet absorption ability, which strengthens its ultraviolet absorption ability. The bishydroxybenzophenone and its derivatives generated after rearrangement can absorb part of the visible light and appear yellow. This will cause the fabric to turn yellow after finishing. In addition, this kind of absorbent has a low melting point, is easy to sublimate, and has a low absorption coefficient, so it is rarely used.
③ Benzotriazoles:
The working principle of benzotriazole UV absorbers is similar to that of benzophenones: the UV absorption effect of benzotriazole is better than that of benzophenone UV absorbers, and can absorb light of 300-400nm, and does not It absorbs light with a wavelength above 400nm, so it will not turn yellow, and has the advantages of volatility resistance and oil resistance. The structure of benzotriazole absorbers is very close to that of disperse dyes, so its application range is limited. It can be processed on polyester using high temperature and high pressure methods. However, if it is to be applied to nylon, wool, silk and cotton fabrics, it needs to be connected in the molecule. an appropriate number of sulfonic acid groups.
④ Triazines:
Triazine and triazole UV absorbers both contain N and rely on the intramolecular hydrogen bonds formed by N and H and the conversion of enol and keto structures to effectively absorb UV rays. They have high absorption of UV light between 280 and 380nm. ability. The absorption effect of triazine absorbers is proportional to the number of hydroxyl groups, so the absorption capacity is stronger than that of benzotriazoles. Its disadvantage is that it has poor compatibility with polymers and the fabric is easy to color after finishing.
⑤ Organic nickel:
The mechanism of action of organic nickel polymers as UV absorbers is different from the above four types of absorbers. They are often classified as quenchers (also known as deactivators, matting agents, laser state quenchers or energy quenchers). ,
The absorption capacity of organic nickel absorbers is low. When the organic nickel polymer molecules receive the energy of ultraviolet light, they are excited into an excited state. When the ultraviolet light is lost, they return to the ground state from the excited state, converting the ultraviolet energy into a low-energy spectrum. Distribute. Thereby reducing the transmittance of ultraviolet rays. Organic nickel absorbers can form chelate complexes with some fiber fabrics under certain conditions, but they are often colored and have limitations in use.
Common UV absorbers are:
① Benzophenone compounds:
It is the earliest UV absorber used. The carbonyl group and hydroxyl group in the molecule of this type of compound form intramolecular hydrogen bonds to form a chelate ring structure. After absorbing ultraviolet light, the internal hydrogen bonds oscillate, the stable chelate ring opens, and the absorbed energy is released in the form of heat energy. In addition, the carbonyl group in the molecule will be excited by the absorbed ultraviolet light energy to form an enol structure. Tautomerism, which also consumes some energy.
Such compounds include: 2-hydroxy. 5 chlorobenzophenone, 2-4 dihydroxybenzophenone, etc. This type of compound has multiple hydroxyl groups, has good adsorption capacity for fibers, and can absorb ultraviolet light from 280 to 400 nm. It is mainly used in polypropylene, polyester, cellulose and other fibers. However, it has almost no absorption of ultraviolet light below 280nm, and sometimes tends to turn yellow. In addition, it is relatively expensive, so it is rarely used in the market.
② Salicylates:
There are also internal hydrogen bonds in the molecules of salicylate UV absorbers. At the beginning, the UV absorption capacity is low and the absorption range is narrow (less than 340nm). However, after irradiation for a certain period of time, the absorption gradually increases. The reason is that molecular rearrangement occurs under ultraviolet irradiation to form a benzophenone structure with strong ultraviolet absorption ability, which strengthens its ultraviolet absorption ability. The bishydroxybenzophenone and its derivatives generated after rearrangement can absorb part of the visible light and appear yellow. This will cause the fabric to turn yellow after finishing. In addition, this kind of absorbent has a low melting point, is easy to sublimate, and has a low absorption coefficient, so it is rarely used.
③ Benzotriazoles:
The working principle of benzotriazole UV absorbers is similar to that of benzophenones: the UV absorption effect of benzotriazole is better than that of benzophenone UV absorbers, and can absorb light of 300-400nm, and does not It absorbs light with a wavelength above 400nm, so it will not turn yellow, and has the advantages of volatility resistance and oil resistance. The structure of benzotriazole absorbers is very close to that of disperse dyes, so its application range is limited. It can be processed on polyester using high temperature and high pressure methods. However, if it is to be applied to nylon, wool, silk and cotton fabrics, it needs to be connected in the molecule. an appropriate number of sulfonic acid groups.
④ Triazines:
Triazine and triazole UV absorbers both contain N and rely on the intramolecular hydrogen bonds formed by N and H and the conversion of enol and keto structures to effectively absorb UV rays. They have high absorption of UV light between 280 and 380nm. ability. The absorption effect of triazine absorbers is proportional to the number of hydroxyl groups, so the absorption capacity is stronger than that of benzotriazoles. Its disadvantage is that it has poor compatibility with polymers and the fabric is easy to color after finishing.
⑤ Organic nickel:
The mechanism of action of organic nickel polymers as UV absorbers is different from the above four types of absorbers. They are often classified as quenchers (also known as deactivators, matting agents, laser state quenchers or energy quenchers). ,
The absorption capacity of organic nickel absorbers is low. When the organic nickel polymer molecules receive the energy of ultraviolet light, they are excited into an excited state. When the ultraviolet light is lost, they return to the ground state from the excited state, converting the ultraviolet energy into a low-energy spectrum. Distribute. Thereby reducing the transmittance of ultraviolet rays. Organic nickel absorbers can form chelate complexes with some fiber fabrics under certain conditions, but they are often colored and have limitations in use.
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