Textiles protection against UV radiation

Textiles can provide protection from ultraviolet rays, the capability of which depends on the type, weave, thickness, and construction of materials as well as chemical finishes present on the fabric, reveal Rajni Yadav and Anjali Karolia.

Ozone layer functions as a protective screen against the detrimental effects of suns hazardous UV radiations. It filters out the UV radiation coming from the sun and prevents the human being from severe skin disease. But due to air pollutants such as fluorocarbons, sulphur dioxide, carbon monoxide and hydrocarbons, etc., present in the environment, a deep imbalance is created in the eco-environment system.

To protect from the detrimental effects of UV radiation, sun protecting materials like creams, lotion, etc., have been in the market since long, but recently awareness of protective clothing is in the forefront. Dermatologists also keep emphasising that the best protective technique to avoid excessive exposure to the sun is to wear textiles to cover your body.

Clothing has the ability to protect the skin from incident solar radiation because the fabric from which it is made can reflect, absorb and scatter solar wavelengths so that it does not penetrate the textile materials. The skin does not therefore come into contact with the radiation. This is however a borderline case. Fabrics differ in their ability to attenuate light in this way because they differ in fibre composition and moisture content as well as in type and concentration of dye, optical whiteners or UV absorbing finishes adsorbed to fibres.

How does UV rays work on fabric?

When incident radiation contacts a fabric, part of radiation is scattered from the surface and the remaining is absorbed by or penetrates/transmits through the fabric. A fraction of the radiation passes through the fibres and spaces between the yarns.

The absorbed radiation is taken by the chromophore in the fibres as well as by other materials present (dyes, de-lustruants, optical brighteners, finishes). Incident light during use may not be perpendicular to the fabric surface, but may contact it at an angle, thereby increasing the scattering and effective cover.

The extent to which a woven or a knitted fabric transmits, absorbs, or reflects UV radiation determines its sun protection properties. The transmission, absorption, and reflection are in turn dependent on the fibre, fabric construction (thickness and porosity) and finish. Therefore it is transmitted radiation that reaches the skin. Higher is the transmission, or lower is the absorption, lower is the protection offered by the textile for the wearer.

Effect of fabric parameters on UV protection

There are various parameters which influence the ultra violet protection of a finished textile. These include the fibre type, cover factor, fabric construction. These are discussed here under (3, 4, 5).

Nature of the substrate

The transmissibility of UV radiation against different textile fibre is different. The raw cotton has higher sun protection factor than bleached cotton because the natural pigments, pectin and waxes act as UV radiation absorber. Wool fibre exhibits maximum protection while silk has intermediate protection value between cotton and wool. Polyamide fibres have less resistance against UV radiation while polyester fibres exhibit high absorption due to their aromatic structure. Acrylic shows low UPF due to the dipole interaction of the nitrile group.

Cover factor

Prof Pailthorpe describes the cover factor in terms of per cent UVR transmission of an ideal textile. He defines an ideal textile as being:

1. i. A fabric in which yarns of the str