The methods for improving the UVR protection of textiles

UVR protective textiles have gained in popularity over the past three decades. With the development of technological innovation, fabrics are given UVR protection by two main methods: chemical and physical.

2.3.4.1 Chemical method

Chemical methods are widely applied in the textile treatment and finishing processes, due to their high efficiency and effectiveness. To improve UVR protection of textiles, there are several methods: 1) the addition of ceramic particles [140] or UV absorbing agents during synthetic fibre production; 2) the treatment of textiles, using UV absorbers or UV shielding agents as either a coating on the surface or as a dye-like particle within the fibre; 3) the use of dyes with UV blocking function to colour the textiles; 4) the addition of fluorescent brightening agents in the dyeing or finishing process; 5) the use of UVR protective laundry additives [141, 142].

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(1) Chemicals

Metallic oxides (such as Al2O3, MgO, ZnO, TiO2, SiO2 and CaCO3) are generally used as an inorganic UV absorber applied in textile treatments. ZnO and TiO2 are the most popular materials used, and these materials have been produced in nanoparticle form for application [139, 143-158]. When the size of nanoparticles is similar to or smaller than wavelengths in the UVR ranges, the ability to absorb UV light is dramatically improved. These nanoparticles have a larger surface area-to-volume ratio and higher surface properties. In the range of UVR wavelength, nanoparticles with 50-120 nm have the best UV absorption, which means they also have the lowest transmissivity at this range of wavelength [139, 143-150, 155]. In the ranges of wavelengths less than 350 nm, ZnO and TiO2 have similar UV blocking effects, however, in the 350-400 nm (UVA range), the UV blocking effect of ZnO is much higher [140, 145]. TiO2, with a particle size of 30-40 nm, is good for blocking UVR in the UV region below 400 nm [159-162]; Al2O3 has strong absorption to the wavelength below 250nm [163]; the reflectivity of SiO2 to the UVR below 400 nm is up to 95% [148, 164]. These metallic oxide nanoparticles also provide other functions to textiles, such as antibacterial properties [145, 157, 165-173] and self-cleaning properties [174-176].

Using organic absorbers, such as substituted benzotriazoles, can make the UVR protection of fabrics very stable with covalent bonds between absorbers and fabrics [177, 178]. Most organic UV absorbers have a conjugated structure and hydrogen bonds and, after absorbing UVR, tautomerism in hydrogen bonding will occur, which means the ability of certain chemical compounds to exist as a mixture of two interconvertible isomers in equilibrium. The ortho-hydroxyl group is primarily responsible for UV absorption. Other organic UV absorbers are generally the derivatives of hydroxy benzonphenones, azimidbenzene, diphenyl ketone, o-hydroxy phenyltriazines, o- o-hydroxyl phenyl hydrazines [13, 140, 179].

UV absorbers can be applied onto textiles by exhaustion from a dye bath, pad-dry-cure, coating [146, 147, 180], sol-gel [167, 181] and magnetron sputtering. Dyes with good UV absorption or blocking generally have functional groups including benzophenone, Phenyl polybenzoxazines three, benzotriazole and salicylates with their chromophore. There are many different approaches for the preparation of nanoparticles, such as hydrothermal, mechanochemical, sonochemical, chemical precipitation, sol-gel, electro deposition method,

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agents can be added into the spinning dope or be blended with a polymer prior to synthetic fibre extrusion [13, 140].

(2) Disadvantages of chemicals

Questions about the risks of using chemicals for UVR protection of materials are highlighted in research. Potential dangers of chemical methods, such as cancers and genetic mutations, can arise from the inappropriate selection and use of some chemicals. The effluent and process waste can also have a negative effect on the environment. The main concern is the toxicity of ingredients of UVR protective agents and the potential health effects associated with these.

With the introduction of nanoparticle-containing agents, there is also a concern over the possibility of damage from nanoparticles.

Phototoxic chemicals. Many chemicals that absorb UVR change shape, chemical structure, energy level, and/or are broken into different compounds when exposed to UVR. These are normally labelled phototoxic. Some chemicals exhibit phototoxicity, such as:

phenylbenzimidazole, which causes intracellular and DNA damage, and Octyl methoxycinnamate which induces photosensitisation [183]; and exhibit photoallergic possibilities, such as: oxybenzon (benzophenone 3) which causes cell damage, and trianilino p-carboxyethylhexyl triazine which causes photodegradation [184]. Chemical remaining in the textiles such as dyes could be harmful to sensitive individuals such as children [185].

Cause of skin diseases. The research on the effects of sunscreens on health found that some chemical ingredients can cause potential skin allergy and carcinogenicity [115, 117, 123]. The UV absorbers can produce reactive oxygen species and generate radicals in the skin and thus may lead to the potential of developing skin cancers, such as melanoma [186] and allergic reactions [184] when the clothing is tighter or the skin excretes sweat [187].

The effect of nanoparticles. Nanotechnology has become an increasingly popular research field [188]. Nanoparticlesof <100 nm are already applied, not only in cosmetics and sunscreens, but also in textile treatments for improving UVR protection. The question that has garnered particular attention is that nano-sized ingredients may cause risks to health [118, 119], for example, small particles may penetrate into the skin [120, 121], and induce skin sensitization and inflammation. Some nanoparticles are insoluble; thereby they may residually rest on the surface of the skin, or enter the circulation system [189]. Other studies, on the contrary, have

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it means the size of nanoparticles is safe and cannot penetrate into, or through, human skin.

The toxic studies on insoluble particles showed that the toxicity is not caused by the particle size but by the chemistry [189]. It is hard to answer this question because the technology is still not sensitive enough so far to distinguish the nanoparticles or soluble ion skin penetration [190].

Besides the safety issues, nanoparticle coating method may affect other properties of the fabrics, such as dyeing capacity, tensile strength, bursting strength, bending rigidity, air permeability, hydrophobicity [157], and fabric friction [139].

Above all, the use of chemicals for UVR protection technology should be interpreted and applied with caution, since people completely rely on UVR protection products to prevent UVR-induced health problems. Also, it is important that to minimize the safety issues from chemicals used in UVR protective products at the same time. The purpose is to prevent wearers against secondary damage from the chemical treatments on the UVR protective products.

Reducing chemical use in textile treatments to achieve good UVR protection is a safe and acceptable way for consumers and can also reduce environmental pollution [191]. Therefore, research to minimise, or eliminate, the use of chemicals in textile UVR protection is important to both the wearer and the environment. Using physical methods can reduce the use of chemicals.

2.3.4.2 Physical method

If UVR protection of textiles is sufficient, then chemical usage could be reduced. Physical methods can maximise UVR protection of textiles. For example, some fibre types may have higher UV absorption than other fibre types at a certain range of UV wavelengths. Accordingly, this fibre type should be the priority of materials selection for UVR protective clothing.

Varying the arrangement of yarns can give different fabric density, for example, fabrics with a higher density should have a higher UVR protection. The arrangement of yarns with a higher fabric density should be taken into account for UVR protective fabric design.

Therefore, research on UVR protection of fibres, yarns and fabrics themselves is necessary for exploiting the capacity of UV absorption, reflectance, scattering and transmittance of textiles.

Beyond this research, the application of UVR protection of textiles and enhancing UVR protection by arranging fibre, yarn and fabric parameters are new directions for the development of UVR protective textiles. This project will address this for further study, with a

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understand the factors influencing UVR protection of textiles, in order to improve the technology, develop the UVR protection and increase performance factors of UVR protective clothing.