Highlight of the article: Growing awareness of the need for sun protection, which is related to the incidence of sun-induced skin damage and its connection to increased UV exposure. Importance UV protective finishes on textiles to combat the harmful effect of UV radiations, its incorporation in fibres, dyes and other processes to create skin friendly UV protective clothing.
The World will be a hollow ball of ice-coated rock without the heat and light of the sun. The sun is warming our oceans, stirring our climate, creating our patterns of weather, and giving energy to rising green plants that provide life on earth with food and oxygen. However, with all the positive attributes, the sunlight also comes with its own set of disadvantages.
Exposure to small amounts of sunlight is beneficial to the species, as it leads to bone growth and vitamin assimilation. Over-exposure to the sun however increases the risk of permanent skin damage. Important protective measures are recommended by dermatologists, like avoiding prolonged exposure to the skin, wearing sunglasses and using cosmetics equipped with sunscreen. Also, the use of textile garments with UV protective finishes.
Ultraviolet Radiations are electromagnetic rays with a wavelength between 100-400nm. Solar UVR that reaches earth has wavelength between 290-400nm. So, depending upon the wavelength, it is classified into three regions:
- Ultraviolet region – A (UVA) (320-400nm)
- Ultraviolet region – B (UVB) (290-320nm)
- Ultraviolet region – C (UVC) (100 nm and 290 nm)
UV-B and UV-A can reach the earth’s surface and cause serious health problems like skin cancer (melanoma), erythema (skin reddening), sunburn, DNA damage, acceleration of skin ageing, eye damage and etc. UV-C is entirely absorbed by ozone layer. Therefore, having the need of UV protective finish in the field of textiles. The UV protection by textile is a function of the physio-chemical characteristics. The wavelengths of maximum danger to skin are 305 -310 nm. Therefore, to be able to exhibit effectiveness in protecting the wearer from solar UV radiation, textiles must have UV protection in the range of 300-320 nm.
The SPF (Solar protective factor) is the ratio of the potential erythemal effect (skin reddening) to the actual erythemal effect transmitted through the fabric by the radiation which can be calculated from spectroscopic measurements. In Europe and Australia, the SPF is known as UPF.
SPF is referred to as the ultraviolet protection factor (UPF). A fabric with an SPF of > 40 is considered to provide excellent protection against UV radiation. UV protective treatment is given to industrial fabrics for awnings, canopies, tents and blinds. Lightweight knitted and woven fabrics should be combined with UV protective finishes to have products like shirts, blouses, T shirts, swimwear, sportswear, etc. as the most exposure to the sun is during the summers. Protection of the skin against the action of solar radiation is a relatively new objective of textile finishing, since the textile does not always guarantee adequate protection. When radiation strikes a fibre surface, it can be reflected, absorbed or transmitted through the fibre or pass between fibres.
The relative amounts of radiation reflected, absorbed or transmitted depends on several factors:
- Fibre type
- Smoothness of the fibre
- Fabric construction
- Moisture content
- UV absorbents and more
Polyester, silk and wool fabrics are better UV blockers than cotton or rayon and polyester fibres even show a better absorption-due their aromatic nature. The transmission can also be reduced due to tighter weave which in turn enables greater protection. With the same weave structure, the SPF of the fabric increases with its thickness so, when there’s a closed texture (having low porosity), there is low transmission of UVR. SPF increases as the relative humidity is raised which is strongly dependent on the type of fibre. Dyes have a considerable influence on UV permeability as they can absorb light in the UVR spectral region. Absorbing property of each dye is different and unique to their dyestuff. Their UV protection power is dependent on concentration. Binary mixture of monochlorotriazine dyes provide higher SPF than the individual ones. Lengthening of the chromophoric chain of two linked dyes owing to their interaction leads to an increase of the SPF of fabric.
UV absorbers are colourless compounds with very high absorption in the 290-400 nm UV range. UV absorbers embedded in fibres transform electrical energy from excitation into thermal energy. They act as radical scavengers and scavengers to oxygen. Cibatex UPF is a two-group UV absorber. Repeated washing is considered stable because of the bi-reactive structure of this absorber. This can be applied to fabrics such cotton and cotton blends. Cibafast W is a derivative of monosulphonated benotriazole. Applied to mixture of wool, silk, polyamide fibres. They are joined by covalent bond to the fibre to permanently enhance the UV defence. UV absorbers used in the dyeing process reduce the intake of dye, except for post-treatment use. They are compatible with the dyes and are applied using standard methods of padding, exhaust, pad thermosol, pad dry cure. UV absorbers are added between 30-40g / l depending on the form and structure of the fibre. The main limitations of UV are that they cannot be applied together with other finishing agents in one bath.
Then also comes special finishing agents like TiO2 particles and Ryosan finish. Synthetic UV absorption can be adjusted by pigmentation by TiO2 particles, which eventually contributes to the dispersion of UV rays. They get wrapped in the fibre and are easy to wash. It also contributes to permanent UV defence development. Rayosan is a commercial UV-absorber which can react with fibres like reactive dyes. Rayosan C paste and CO liquid products are used for finishing cellulose. The Rayosan finish has a good washing fastness.
The need to shield humans from toxic UV radiation is clear when confronted with a thinning ozone layer and the rise in the number of skin cancer cases. Textiles with a sufficiently high SPF rating are a part of combating skin cancer and this will require the development of stronger UV absorbers suitable for low SPF fibres. Sun security requires a combination of sun avoidance and the use of protective clothing and accessories. The three ways of guarding against the deleterious effects of UV radiation are to limit the exposure period to sunlight, using sunscreens and protective clothing.
Itisikta Pani (NIFT Bhubaneshwar)