Cellulosic fabrics transmit UV A and UV B equally with the transmittance ratio (TA/TB) 0.9. When dyed with the reactive dyes, the UPF increases from 4.7 to 5.0 - 14.0 depending upon the concentration, which is not sufficient to satisfy the minimum requirements. Some of the vinyl sulphone dyes and monochlorotriazine dyes possess UVR absorption characteristics, which also increase with the concentration. Cellulosic fabrics dyed with these dyes show reduced UVR transmission from 24.6% to 10-20% and 27.8% to 8-22% for UV A and UV B respectively. When mixtures of these dyes are used, the UPF increases synergistically. Some combinations of disperse reactive mix can give prolonged UV protection with a UPF of 50+ for PIC blends.

Optical brightening agents or fabric whitening agents are used at the finishing operations, as well as in the wash cycles, and their effect on UPFs has been demonstrated extensively in the past. Optical brightening agents are often applied to enhance the whiteness of textiles by UV excitation and visible blue emission. The phenomenon of excitation and emission is caused by the transition of electrons involving p-orbitals from either conjugated or aromatic compounds.

Most optical brighteners have excitation maxima within the range of 340 - 400 nm. OBA can improve the UPF of cotton and cotton blends, but not of fabrics that are 100% polyester or nylon. The presence of OBA in the PIC blends (67/33) to the extent of 0.5% can improve the UPF from 16.3 to 32.2, which is more or less closer to that obtained using the UV absorbers with 0.2% (UPF 35.5). Washing the fabrics leads to a loss of UPF in the case of OBA-treated fabrics, and the UPF reaches the level of that in untreated fabric after 10 washes, which shows the semi-permanent nature of the finish and protection. Another limitation of many OBAs is that they mostly absorb in the UVA part of the day light spectrum (93%) but have a weak absorption in UV absorption around 308 nm (92%), which plays an important role in skin disease.

References:

1. Saravaban D.," AUTEX Research Journal" ,7(1 )2007.53-62
2. Mallik S.K., Arora T., "UV Radiations: Problems and Remedies", Man Made Textiles in India2003 (5) 164 -169
3. Achwal WB., "Use of UV Absorbers in Textiles", Colourage 1995 (10)44 -45
4. Reinert G., Schmidt E., Hilfiker, "Use of UV Absorbers in Textiles", Textilverendlung 1994 (75) 606
5. Gupta K.K., Tripathi V.S., Ram H., Raj H., "Sun Protective Coatings", Colourage 2002 (6) 35 -40
6. EI Zaher N.A., Kishk 5.5., "Study of the Effect of UVR on the Chemical Structure, Mechanical Properties and Crystallinity of Nylon - 6 Films', Colourage 1996 (11) 25 - 30
7. "Microscopical Observations of the Abrasive and Ultraviol Deterioration of NomexAramid Fibre", Textile Res. J. 1977 (3) 171 -177
8. Hunt R., "Opportunities in UV Protection" Knitting International200J( 51 -53
9. Gantz G.M., Sumner W.G., "Stable Ultraviolet Light Absorbers", Textile Res. J 27 (3) 244 -251
10. Hustvedt D., Crews P.c., "The Ultraviolet Protection Factor of Natural Pigmented Cotton", The Journal of Cotton Science 2005 (9) 47 - 55
11. Krizek D.T., Gao W., "Ultraviolet Radiation and Terrestrial Ecosystem" Photochemistry and Photobiology 79 (5) 2004 379 - 381
12. Sunscreen - Wikipedia, the free encyclopedia.htm
13. http://en.wikipedia.org/wiki/acacia-catechu
14. http://www.bioone.org

About The Authors:

Neha Singh is an Assistant Professor, Department of Textile Design, NIFT, New Delhi & Prof. (Dr.) Suman Pant is associated with Department of Home Science, Banasthali University, Rajasthan.

Originally published in: Textile Review, August-2010