34 UV Protective Finishes

S. Karpagam Chinnammal

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1. Introduction

 

The Ultraviolet light radiation from the sun is absorbed by ozone layer or reflected back into space, hence only a little amount reaches the earth’s surface. But in recent years, the whole world is suffering from all kinds of pollution, consequently damaging the earth’s protective ozone layer. The reduction of ozone layer in the upper atmosphere have led to increased danger of exposure of skin to UV radiations resulting in increasing risk of skin cancer. So, the importance of UV protective finish has substantially increased.

 

2.  Learning objectives

  • To understand about Ultraviolet Radiation and its effects
  • To understand the Need, Application and Use of Ultraviolet Protective Finish To get an insight into the assessment and standards for UV protection
  • To learn about the Factors contributing to the UV protection of textiles

   3.  Ultraviolet Protective Finish

 

Ultraviolet protective finish is a specialty finish for protecting the fabric from UV radiation so that it protects human underlying tissues from UV radiation. These finishes include chemical compounds that absorb energy in the UV zone of the electromagnetic range. Sun protective finish or UV blockers are other names for this finish.

 

4. What is UV Radiation?

 

Sunlight is the natural source of energy that reaches the surface of the earth. This solar radiation consists of infrared, visible light (from red to violet) and ultraviolet radiation. Ultraviolet radiations roughly contribute to 10 % of sun’s energy, most of the harmful radiations emitted by the sun are absorbed by the atmosphere and only about 5 % of the harmful radiations reach the surface of the earth.

 

Electromagnetic radiations of wave length in the range of 100nm to 400 nm are referred to as UV radiation or UV rays. Solar UVR that reaches the earth’s surface contains radiation in the range 290 to 400 nm due to atmospheric absorption of the shorter wavelengths below 290nm.

 

Based on the range of wavelength, the UV radiations are categorized into three regions.

 

UVA-Ultra violet radiation in the range 320nm to 400nm have longer wavelength which on exposure to skin penetrates and generally causes wrinkling and speeds up aging of the skin. UVA accounts for 90% of total UV radiation reaching the earth surface.

 

The shorter UVB radiation in the range 290nm-320nm is much stronger and dangerous to the skin and eyes than UV A. UV-B radiations on excessive exposure penetrate few millimeters of the skin and correspond to greater damage of the human skin like sun burns, redness and skin cancer. UVB is mostly absorbed by the Ozone layer and only a small amount reaches the earth’s surface, but it’s potential in causing sunburn is much more than UVA.

 

The most injurious to the skin and eyes are the shortest UVC radiations in the range 100 nm to 290nm. It is completely absorbed by the atmosphere and does not reach the earth so it is not considered a health concern.

 

5.  Effects of UV radiation

 

5.1.On humans

 

Ultraviolet rays represent a very small portion of the solar spectrum but affect all living organisms and their metabolism. Energy level is inverse to wave length, so the UV radiations the shortest wavelengths in the spectrum possess high energy and are harmful to the human skin and eyes.

 

These radiations can cause a range of effects from simple tanning to highly malignant skin cancers, if unprotected. Penetration of UV rays into the top layer of the skin leads to damage in the lower layer and prolonged exposure may lead to severe and chronic reactions and damage, such as premature ageing of skin, wrinkles, photo dermatitis, phototoxic reactions to drugs, erythema (skin reddening), sunburn, increased risk of melanoma (skin cancer), Eye Damage (Opacification of the Cornea) and DNA damage. And with decrease in ozone layer these are expected to increase. This has forced the development of UV protection finishes.

 

5.2.On textiles

 

UV radiations is not only harmful to the living creatures; it is also responsible for deterioration in useful properties and service life of materials like textiles, furniture etc. UVR accelerate the physical and chemical deterioration processes of the polymer of textile product, due to absorption of energy and ultimately leads to strength loss of the textile product, yellowing of cellulosics, photo-oxidation of pololefins etc. UV radiations also attack the dyes present in the goods resulting in spotting and loss of colour.

 

The degradation can be reduced by using UV stabilizers, which scatter the energy acquired from these ultraviolet radiations in the harmless manner thus, protecting the material and getting themselves destroyed in the process.

 

6.  Ultraviolet protection

 

Stratospheric ozone absorbs the ultraviolet radiations from the sun and protects the earth from the harmful radiation. But ozone is getting depleted due to the presence of air pollutants such as fluorocarbons, sulphur dioxide, carbon monoxide and hydro carbons present in the environment. With increase in depletion of ozone layer there is steady increase in the amount of UV rays reaching the earth. It is predicted that one percent decrease in ozone concentration will increase the rate of skin cancer by 2 to 5 %. As too much exposure of these radiations leads to harmful effect it is highly important to guard the skin.

 

The best ways to care for oneself against the harmful effects of UV radiation are: avoiding outdoors specially during midday, using sunscreen creams or lotions and wearing protective clothes. Role of sun block creams is to absorb or reflect UV rays. Apart from sunscreen lotions, textile materials and accessories made of textile materials are chiefly used for UV protection. Protection offered by UV protective clothing is more durable than sun screens.

 

The basic purpose of a garment is to protect the wearer from weather, but it is also a supreme means of protecting oneself from harmful UV rays. The UV rays incident on the fabric is absorbed, reflected or transmitted. Higher the transmission of UV rays through the fabric lower is the protection offered by the fabric. The extent of protection of skin by textile materials greatly depends on the fabric structure. Protective effect of clothing can be improved by wearing thick materials, darker colours or several layers one on top of other. The UV blocking property of a fabric is enhanced when a dye, pigment, delustrant or ultraviolet absorber finish is present that absorbs ultraviolet radiation and blocks its transmission through a fabric to the skin. Various nano finishes, using titanium dioxide and zinc oxide, also increase the UV absorbency. In order to achieve a balance between a high UV protection factor, wearing comfort and durability, in recent years special fibres with built in UV protection have been developed. They contain titanium dioxide, which reflects and/or absorbs harmful UV radiations so that it does not reach the skin.

 

Fabric treated with UV absorbers ensures that the clothes deflect the harmful ultraviolet rays of the sun, reducing a persons UVR exposure and protecting the skin from potential damage. The extent of skin protection required by different types of human skin depends on UV radiation intensity and distribution in reference to geographical location, time of day and season. This protection is expressed as SPF or UPF higher the SPF/UPF value better is the shield against UV radiation

 

7.  Sun protection factor (SPF)

 

Sunscreens are rated by SPF; it is an assessment of the amount of protection provided by the sun screen against UVR. SPF is the factor by which the period of exposure to sun can be extended without reddening skin. For ex SPF 10 means, one can stay 10 times longer before burning than if one was wearing no sunscreen. It ranges from 2-50+.

 

8.  Ultra violet Protection Factor (UPF)

 

UPF measures the effectiveness of textile fabrics in shielding the human skin from UV radiation. It is expressed as the relative amount of time required for the skin to show redness with and without the textile material under regular exposure to solar radiations. If a person experiences skin redness on exposure to sun after 10minutes, then on wearing a textile material of UPF 20 he would experience the same amount of skin redness after 200 minutes. A UPF score of 30 indicates that only 1/30th of the UVR striking the fabric surface essentially passes through it. Higher the UPF of a textile, the better is its ability to guard the skin it covers.

 

UPF Values

 

S.No UPF values UV protective range
1 15-24 Good protection
2 25-39 Very Good protection
3 40-50,50+ Excellent protection

 

9.  UV Absorbers

 

UV stabilisers based on their method of action are classified into three different categories – UV absorbers, Quenchers, Hindered amine light stabilizers (HALS). HALS provides very good resistance against UVR. UV absorbers strongly absorb UV in the wavelength of 290-360nm and provide good protection from UVR. They are either organic or inorganic colorless substances that absorb UV light effectively and convert the energy into relatively harmless thermal energy without itself under going any appreciable irreversible chemical change or inducing any chemical change in the textile molecule. Ultra violet absorbers have UPF rating of UPF 50+ to UPF 500+.

 

9.1. Organic UV absorbers

 

The important groups of UV absorbers are 2-hydroxybenzophenones, 2-hdroxypheny benzotriazoles, 2-hydroxphenyl-s-triazines.

 

Organic UV absorbers are mainly derivatives of o-hydroxyl benzophenones, o- hydroxyl phenyl triazines, o-hydroxyl phenyl hydrazines. The ortho hydroxyl group in the molecule helps in absorption and to make the compound soluble in alkaline solution. Organic compounds like benzotriazole, hydro benzophenone and phenyltriazine can be applied by normal padding or coating. Ortho hydroxyphenyl and diphenyltriazine derivatives have excellent sublimation fastness and self dispersing formulation. It can be applied by pad thermosol process and also in print paste.

 

9.2. Inorganic UV absorbers

 

The existence of inorganic pigments in the fibers helps in better dispersion of light from the substrate, thus providing better protection. Metal oxides like ZnO as UV-blocker are more stable when compared to organic UV blocking agents.

 

The most common nanoparticles used to impart UV protection are ZnO, TiO2, SiO2, Al2O3 etc. They provide a protection benefit by reflecting, scattering or absorbing harmful UV. Inorganic fillers are formed from micro fine particles of titanium dioxide or zinc oxide that reflect the incident UV light like tiny mirrors.

 

9.2.1. Zn O nanoparticles

 

ZnO has a high absorption band .Apart from its exceptional UV absorption properties , ZnO has numerous other advantages like increased surface area, it does not migrate, it is not degraded by absorbed light and may improve the mechanical, optical and electrical properties of the polymer.

 

9.2.2. TiO2 nanoparticles

 

Titanium dioxide and other ceramic materials have high absorption power in the UV region of 280-400 nm and results in dispersion of UV rays and thus make it less permeable to UV rays. It also shows good photo catalytic and antibacterial properties.

 

9.3. Commercial UV absorbers include Rayosan, Tinofastcel and Ciba Geigy For practical use, UV stabilizers must demonstrate most of the following properties Maximum absorbency in the UV region ( 280-400nm )and no absorbency in visible regionStable towards electromagnetic radiation and should not get damaged or used up in fairly short timeDisperse the absorbed energy in such a way so as to cause no degradation or colour change in the medium it protects

 

Thermally stable to processing conditions and chemically inert towards other additives present during production and subsequent use It should not be noxious If used in sunscreen lotion it must not irritate the skin

 

10. Finishing with UV absorbers

 

UV absorbers are compatible with dyes and are applied by normal padding, exhaust, pad thermo sol, pad dry cure methods. UV absorber 30 -40 g /l is applied at 60°C with 20 g/l Sodium chloride using a padding mangle at 80% expression. After padding the fabric is dried at 130°Celsius for 5 minutes and cured at a temperature of 170 -180 °C Celsius for 3 minutes.

 

11. Assessment of Ultraviolet Protection of textiles

 

Two types of test methods are used to analyse the UV resistance of the fabric -in vivo (SPF) and in vitro (UPF). In vivo testing involves tests made on the back of volunteers with healthy skin. In vitro testing makes use of a spectrophotometer in the range of 280 -400nm to calculate UPF of the material.

 

The transmission of ultraviolet radiation (UV-R) through a specimen is measured on a spectrophotometer or spectro radiometer at known wavelength intervals. The UPF is calculated as the ratio of the erythemally weighed ultraviolet radiation irradiance at the detector with no specimen to the erythemally weighed UV-R irradiance at the detector with a specimen present.

 

12. Standards for UV protective textile

 

There are various methods for measuring the UPF:

 

The Australian/New Zealand standard (AS/NZS 4399:1996) , The European standard EN 13758 -1, American Association of textile chemists and colourists test method (AATCC-183) and the UV standard 801.

 

These test standards define different condition for the material being tested. The Australian /New Zealand (AS/NZS 4399:1996) and the tests under EN 13758-1 and AATCC 183 only require testing to be carried out on new textiles that are dry and un stretched.

 

The UV standard 801 is considerably more practical: for clothing textiles, the UPF is measured on the stretched, wet textile and after mechanical wear and tear caused b wearing and washing.

 

13. Factors contributing to the UV protection of textiles

 

UV protection of fabrics depends on the following parameters

 

13.1. Fiber characteristics– Natural fibres have lower ultraviolet absorption than synthetic fibres. Grey cotton is found to offer greater UV protection than bleached cotton because of the presence of natural absorbers pectin, wax etc. Wool and silk absorb more ultraviolet rays because of the presence of natural tannins and lignins. Wool has greater UPF among natural fibres. Generally silk fabrics are thin hence found to have lower UV protection than wool. Among synthetic fibres polyester has maximum UV absorption because of it aromatic structure. Polyamide fibres are less resistant against UVR. UVR property of synthetic fibres can be improved by using additives like Tio2 an UV obsorber Prior to fibre extrusion in manufacture. Specialised fibres have been developed like sun modal fabrics with UV absorbent properties. Higher transmission of UV radiation is observed in the case of bright fibres (viscose) than dull fibres.

 

13.2. Yarn structure– Twist of the yarn relates to the packing density of the fibre in the yarn structure. This corresponds to the air space within the fabric structure hence contribute to the transmittance of the UV rays through the fabric. The yarn twist becomes one of the major determinants of UPF especially of knitted fabrics as it affects the porosity of the fabric.

 

13.3. Fabric construction parameters-Fabric porosity is the most imporatnt parameter deciding the UPF of the fabric. Fabrics with closely packed threads are found to have higher UPF.

 

UPF=100/Fabric porosity

 

Based on the above expression, it may be understood that UPF is highly correlated with fabric porosity. Porosity should be below 1.5-2%. In knit structure, the loop structure facilitates porous structure hence transmit more UV rays than woven fabric. Light weight loosely woven fabrics have minimum UV protection which is preferred to use in hot outdoor climate.

 

The weave or construction of fabrics is the main factor affecting UVR coming through the fabric. The more closely woven fabric the less UVR is transmitted, Twill weave is much denser than satin or sateen weave due to its high compactness and will have better UPF. The cover factor of the fabric is the main parameter for UV protection.

 

UPF also increases with fabric weight and thickness. Heavier clothing minimizes UVR transmission by virtue of having smaller spaces between yarns thus blocking more radiation and thicker fabrics have better UV protection.

 

13.4. Stretch-Stretch offers poor protection than inelastic fabrics as it increases the pore size and found to increase the UV transmittance. Loose Fit garments offer increased air space between the skin and fabric, which reduces the transmittance of UV rays to the skin.

 

13.5. Effect of chemical treatment-

 

13.5.1. Dyeing modifies the proportion of UV light transmitted through fabrics and increases UV protection performance. Depending on their chemical structure, the absorption band of many dyes used to colour textiles extends into the UV spectral region and hence dyes act as UV absorbers and increase the UPF of the fabric. Fabrics with darker colours transmit less UV light than light colours and darker shades of the same hue have higher UV protection ability. Increased concentration of dye of same colour on same fabric led to darker shade of fabric, which also increased the UPF. It is because more dyes were presented to absorb UV lights and thus lower transmission was achieved. Eg navy blue transmits less UV than light colours

 

13.5.2. Bleaching process lowers the UPF of cotton fabrics as it removes the natural absorbers.

 

13.5.3. Flourescent whitening agents –Fabrics treated with Optical brighteners ie Flourescent whitening agents reflect or absorb UV rays hence cater to better protection.

 

13.5.4. Ezymatic treatment-Cellulase widely used in biopolishing removes protruding fibres from the fabric surface. It is found that the enzymatic treatment increased the UPF of the fabric

 

13.6. Moisture- Wet fabrics have lower UPF .Water in the interstices of the fabric reduces the scattering effect and therefore increases its UV radiation permeability

13.7. Laundering-causes changes in physical properties of fabrics and hence affects UV blocking performance. Shrinkage of fabrics occurs after laundering in cotton fabrics as the fibre swells closing the space

13.8. UV Absorbers- Finally the specially designed absorbers is the strongest way to protect from UV radiation

  1. Application of UV protective finish

Since the most probable time for long term solar exposure is in summer, the articles for UV protective finish are lightweight woven and knitted fabrics intended for producing shirts, blouses, T shirts, swimwear, beach wear, sportswear, and the like. Industrial fabrics designed for awnings, canopies, tents, hats, umbrellas, shoes, baby carrier cover and blinds may also benefit from UV protective treatment. The area of most rapid consumption of sun protective textiles is geo textiles, packaging textiles, protection textiles and agricultural textiles.

  1. Characteristics of UV finish

It is a specialty finish for protecting the fabric from UV radiation. Protects human’s underlying tissues from UV radiation. Protects against short wavelength radiation i.e. from 100 – 400 nm, Non-yellowing or fading of fabric. Should be applied during dyeing under a reductive process. Applicable by exhaust as well as padding method.

  1. Conclusion

Due to depletion of ozone layer, intensity of UV radiation reaching the earth surface has increased, affecting human beings, and therefore UV protection is necessary. Human skin is vulnerable to UV exposure and hence needs to be protected. Sunscreen is applied to face and hands however other parts of the body require to be protected by means of UV protective clothing. These are developed through various finishing techniques using UV absorbing chemicals.There is a growing consumer demand for increased sun protection which has driven the sun care market into innovative areas, including UV protective clothing.

you can view video on UV Protective Finishes

REFERENCE

 

  1. http://www.fibre2fashion.com/industry-article/1/69/uv-protection-finishes1.asp
  2. http://www.autexrj.org/No1-2007/0192.pdf
  3. G.Sivashankari ,Ultraviolet protection properties of knitted fabrics, The Indian textile journal, May 2015 Vol CXXV No.8 Pp-94-95
  4. Vinay G Nadiger and S R shukla, Developments in UV protective textiles-II, Asian dyer, December 2012, January 2013 p 26-29
  5. www.autexrj.com/cms/zalaczone_pliki/6-07-1.pdf-pdf
  6. http://www.autexrj.com/cms/zalaczone_pliki/6-07-1.pdf
  7. http://www.tikp.co.uk/knowledge/material-functionality/uv-resistance

WEBLINK

 

http://www.t-pot.eu/docs/HGK/HGK_20090922_5INFMP_Zimniewska_Innovations in UV protection by textiles.pdf