PPE

what is the anti ultraviolet finishing of textiles and what are the common UV Absorbents?

With the continuous improvement of people’s quality of life, the research on the impact of ultraviolet on human body is also in-depth. Since the decrease of stratospheric ozone layer thickness and the existence of ozone hole were observed in Antarctica in October 1982, the problem of ultraviolet radiation caused by the destruction of ozone layer thickness has become one of the focuses of increasing attention

ultraviolet

ultraviolet is a kind of electromagnetic radiation. The 1nternational Commission on illumination (C1E) divides the ultraviolet in solar radiation into three wavelength bands

long wavelength UV-A (wavelength 3l5nm-400nm). UV-A accounts for 90% of the total amount of ultraviolet rays reaching the ground, causing skin blackening and even skin cancer

medium wavelength UV-B (290nm-3l5nm). This is the cause of sunburn

short wavelength UV-C (wavelength l80nm-290nm). Can be absorbed by the ozone layer, can not reach the ground

it can be seen that UVA and UVB are the most harmful to human body

the factors that influence the anti ultraviolet property of fabric

the anti ultraviolet property of fabric, as the name suggests, is the ability of fabric to absorb or reflect ultraviolet. At present, UPF (abbreviation of ultraviolet protection factor) is mainly used to express the ability of fabric to protect against ultraviolet in the world. 1t is the ratio of the average amount of ultraviolet radiation to unprotected skin to the amount of ultraviolet radiation after the fabric to be tested is covered. The value and protection grade of UPF are shown in the table

influencing factors

1 yarn material

textile fiber itself has a certain absorption and shielding effect on ultraviolet, and different types of fiber have different absorption and transmission ability for ultraviolet. The lower the absorption capacity, the higher the transmittance and the worse the anti ultraviolet performance

in all widely used fiber materials, polyester contains benzene ring, which has high UV absorption capacity; The ability of nylon to absorb ultraviolet light is poor; There are aromatic amino acids in wool, silk and other protein fibers, which have strong absorption of light in the wavelength of less than 300 nm, and their anti ultraviolet performance is between that of polyester and nylon

for cellulose fiber, the UV transmittance of bleached cotton yarn and viscose fabric is relatively high, while the UV protection coefficient of unbleached cotton yarn fabric is slightly higher because of its natural pigment and lignin as absorbents; Flax fabric has good anti ultraviolet performance because of the groove like voids in the fiber and many voids on the tube wall; The content of sodium copper chlorophyllin in bamboo fiber is a safe and excellent ultraviolet absorbent. 1ts ultraviolet resistance is much better than that of cotton fiber, ramie and flax fiber

in recent years, the method of adding shielding agent can effectively improve the anti ultraviolet ability of fiber

2 yarn structure

the yarn twist affects the tightness and surface properties of the yarn, and then affects the opening degree of the fabric and the transmission performance of ultraviolet light. Some researchers believe that the main influencing parameters of yarn anti ultraviolet performance are yarn thickness (or diameter) and yarn crimp rate. Because these parameters have direct influence on fabric structure, the influence of yarn structure can be incorporated into the influence of fabric structure parameters

3 fabric structure parameters

the fabric structure parameters that affect the UV protection performance of textiles are mainly weave structure, tightness, thickness, etc. The fabric structure is related to the tightness, density, thickness and mass per unit area of the fabric. The fabric structure determines the space geometry and porosity of the fabric. 1t is generally believed that the influence of its anti ultraviolet performance mainly lies in the two parameters of compactness and thickness. The tighter and thicker the fabric is, the better its anti ultraviolet performance is

4 color

the color of fabric is determined by the absorption characteristics of dyes in the visible light region, which is different from the absorption characteristics of dyes in the ultraviolet light region. Therefore, the color of fabric is not the main factor determining the anti ultraviolet performance of fabric

at present, there is a consistent conclusion on the influence of color on the anti ultraviolet properties of textiles: some dyes have strong absorption capacity in the visible spectrum region, and also have partial absorption capacity in the ultraviolet spectrum region; Generally, the UV protection performance improves with the increase of color depth, and dark blue and black have the best UV protection performance in various colors

5 after finishing

in the finishing process, the UV shielding agent can be fixed on the surface of the fabric to improve the UV resistance of the fabric< According to the anti ultraviolet mechanism, it can be divided into reflection type anti ultraviolet finishing agent, absorption type anti ultraviolet finishing agent and nano type anti ultraviolet finishing agent 01 reflective anti ultraviolet finishing agent reflective anti ultraviolet finishing agent has no absorption effect on ultraviolet, but only depends on the reflection of light to reduce the transmittance of ultraviolet. Also known as UV shielding agent. Most of the shielding agents are metals, metal oxides and salts, such as Ti02, Zn0, al02, kaolin, talcum powder, carbon black, iron oxide, lead oxide and CaC03, etc. the UV reflectance of these shielding agents at 310-400nm can reach 95% although the UV shielding agent has unique advantages, the finished fabric has poor air permeability, handle and washing resistance, and the color, fastness and whiteness of the fabric are decreased, some even cause allergic reaction. Therefore, this kind of finishing agent is mostly used for sunshade, tent and so on, but rarely used for clothing fabrics 02 absorption type anti ultraviolet finishing agent absorption type anti ultraviolet finishing agent is also known as ultraviolet absorbent, which can strongly and selectively absorb high-energy ultraviolet rays and release them in the form of other low-energy forms (such as long wavelength light or heat), so as to avoid the harm of ultraviolet rays to human skin, The absorbent itself is not damaged by ultraviolet radiation. 1ts absorbent principle is generally considered as the transfer of intramolecular protons: the hydroxyl group in the structure forms an intramolecular six membered ring containing hydrogen bond with the N or O atoms in the nearby structure. The six membered ring is opened after absorbing energy by ultraviolet irradiation. With the conversion of enol type and ketone type structure, the harmful energy is converted into harmless light wave or heat energy release, and the six membered ring is closed again as a fabric UV absorber, it should have the following conditions: (1) it is safe and non-toxic, has no allergic reaction to human body, and cannot pose a threat to human health< (2) meet the requirements of environmental protection< (3) good solvent and washing resistance< (4) there was no color phenomenon after absorbing ultraviolet light (5) it has little or no effect on the whiteness, fastness, strength, handle and other physical properties of the fabric and the style of the fabric (6) it has certain stability different kinds of UV Absorbents 03 nano anti UV finishing agents the development of nano materials provides a new way for UV shielding agents. Compared with general UV shielding agents, nano UV shielding agents have large specific surface area, high surface energy, easy to combine with materials, small particle size, low diffuse reflectance to visible light, high transparency, and little influence on the style of finished fabrics the UV absorption mechanism of nano materials is different from the above organic absorbents. Take nano-TiO2 as an example: the electronic structure of TiO2 is a full valence band and an empty conduction band, the band gap energy is 3.oev ~ 3.2eV, and the band gap width is generally below 3.oev. When TiO2 absorbs ultraviolet photons with energy greater than or equal to its forbidden band width, the electrons in the valence band will be excited to the conduction band, resulting in highly active and free-moving photogenerated electrons (E -) and holes (H +) the electron hole pairs generated by nano-TiO2 absorbing ultraviolet lines will re combine when various redox reactions occur, 1t releases energy in the form of heat or fluorescence, on the other hand, it dissociates into free holes and free electrons that migrate freely to the surface of the lattice or other reaction sites, and is immediately captured by surface groups. Under normal circumstances, titanium dioxide surface water will be activated to produce surface hydroxyl, capture free holes, form hydroxyl radicals, and free radicals will absorb oxygen to produce superoxide radicals, killing the surrounding bacteria and viruses. Therefore, the finished fabric not only has the ability of anti ultraviolet, but also has the effect of sterilization Deng ye and others finished cotton fabric with self-made nano titanium dioxide finishing agent. The finished fabric not only has excellent ultraviolet resistance, but also has good washing resistance, and does not affect the air permeability, handle and other properties of the fabric. Li Hong et al. Studied the anti ultraviolet finishing of flax fabric with nano-zn0, and also achieved good results< source: China Textile Joint 1nspection Co., Ltd., Quanzhou, “anti ultraviolet finishing of textiles” * the weather in summer is dry, hot and strong ultraviolet, which has become an important problem faced by the front-line workers in the oil industry in the field work, and the relevant industries have included moisture absorption and quick drying as a comfort function in the basic assessment index of summer protective clothing. However, the working environment with strong ultraviolet radiation in summer may cause potential health hazards to the front-line workers after repeated research by technical experts of special fabric R & D center of Jiangnan Branch of China Academy of Textile Sciences, we successfully developed “Lanxiang” anti ultraviolet line & amp; made of 6f30d polyester based high-performance conductive material and fine denier anti ultraviolet fiber through special production process; Anti static safety protection tooling fabric, which integrates anti-static protection performance, anti ultraviolet function and high permeability Qigong function, has a soft feel

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