Ultraviolet protection properties of knitted fabrics
Double knitted fabrics offer higher ultraviolet protection than single knitted fabrics owing to their heaviness and thickness, finds G Sivashankari.
Sunlight is the inherent source of energy reaching the earth´s surface. Approximately 5 per cent of the incident sunlight constitutes ultraviolet radiations. The UV spectrum present in the sunlight has shorter wavelength ranging from 280 nm?400 nm. The Ultraviolet radiations possess high energy and are harmful to the human skin and eyes. Based on the range of wavelength, the UV radiations are categorised into three regions. The UV-Aradiations (320 ´ 400 nm) have longer wavelength, which on exposure to skin penetrates causing premature ageing and does not make any visible effect to the skin. The shorter UV-B radiations (290´320 nm) penetrate few millimetres and damages the skin causing sun burns. The shortest UV-C radiations are the most injurious to the skin but hardly reach the earth´s surface. Hence the UV ´ B radiations on excessive exposure corresponds to greater damage to the human skin like sun burns, inflammation and skin cancer.
Ultraviolet protection: Ozone layer present in the earth´s atmosphere absorbs the Ultraviolet radiations from the sun acting as a protective shield blocking the harmful radiations from the sun. With increase in depletion of ozone layer due to emissions from the earth´s surface there is steady increase in the amount of UV rays reaching the earth. As excessive exposure of these radiations leads to detrimental effect it is highly significant to protect the skin. Studies have proved clothing as an ideal means of protecting the skin from 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 degree of protection of skin by textile materials largely depends on the fabric construction parameters.
Ultraviolet Protection Factor (UPF): UPF refers to the degree of protection of the clothing covering the human skin from ultraviolet radiations. It is the ratio between the time duration to cause skin redness with and without the textile material under constant exposure of solar radiations. If a person experiences skin redness on exposure to sun after 10 mins, then on wearing a textile material of UPF 15 he would experience the same amount of skin redness after 150 mins, which may be better understood by the table: