ABSTRACT

Beside the vital and powerful role of sun in our everyday lives the overdose of UV radiation on skin can lead to potential skin damage from exposure to the sun's ray. Compare with visible light that interacts with dyes UV radiation interacts with ultraviolet absorbers and fluorescent whitening agents. Middle UV-rays (UV-B region, l=280-315 nm) causes acute and chronic reactions and damages such as skin reddening or increased risk for other diseases.

For such reason it is important to protect the people from the ultraviolet radiation falling on garments and sun-screening textiles such as tends. The level of such protection of fabric depends of a large number of factors as the type of fiber, porosity, density, moisture, color and FWA in the case of white textiles. In this paper cationized cotton fabric was treated with UV reactive apsorber on the base of oxalanilide, Tinofast CEL, to improve the UPF of fabric. Exacust method was applied following peroxide bleaching and optical bleaching procedure. For optical bleaching three stilben derivates as optical brighteness agents were used in wide concentration range. The UV protection factor (UPF) measurements were done using Varian Carry-50 AnAs UV-Vis spectrophotometer, the whiteness degree and yellowness by Datacolor Spectraflash 600 PLUS-CT and relative intensity of fluorescence by Carl-Zeiss Fluorometer. The aim of the paper was to study the FWA's fluorescence changes of sunprotected white cotton fabric.

1. INTRODUCTION

Ultraviolet skin protection by fabrics has been a topic for ten years but UV absorbers have been on the market for over twenty years to protect various substrates (tires, coated fabrics, etc.) against UV degradation or to improve light fastness. Fabric can reflect, absorb and scatter solar wavelengths that reaches the earth's surface in the range of 280 nm to 3000 nm, consisting of UV, VIS and IR radiation, Menter and Hatch (2003). The UV radiation represents 7 % of total solar emission. It is divided into UV-A (400-320 nm), UV-B (320-280 nm) and UV-C (<280 nm). UV-B rays are only partially absorbed by ozone and reach the earth causing erythema (sunburn), sun tanning, photocarcinogenesis and "photoaging" although UV-B is a small fraction, about 10 % of total UV radiation, Geis et al. (1998) and Neves (2003).

On the basis of good fabric UV protection it is clear that clothing has the ability to protect the skin from incident solar energy. This protection depends on fiber composition and moisture content, type and concentration of dye, optical brighteners and UV-B protective agents. Optical bleached textiles absorb the UV light and remitt it as the bluess, redness and greeness light resullting in the textile that appears whiter, Shenai (1999). According to this fact FWAs on textile can influence on UPF values in the wide range of FWAs concentration, GrancariC and SoljaCiC (1980).

Ultraviolet protection factor, UPF values (Table 1) indicates the ability of fabrics to protect the skin against sun burning. It indicates how much longer a person can stay in the sun with the fabric covering the skin as compared with the uncovered skin to obtain same erythemal response. The UPF can be calculated by the following equation Menter (2003):

where:

E (l)= spectral weighting function of erythemal action spectra
S (l) = spectral irradiation for appropriate solar radiation spectrum [W m-2 nm-1]
t(l) = spectral transmittance through specimen
Dl = appropriate wavelength measuring interval [nm]

2. MATERIAL AND METHODS

The fabric used was a circular weft knitted fabric S-307 of 100 % carded raw cotton (123 g/m2), 87 cm wide in tubular form, having 11 wale/cm and 14 courses/cm. Fabric was desized, traditionally scoured with NaOH and enzimatically scoured with BioPrep 3000L, than bleached in peroxide baths, GrancariC, PuSiC and Tarbuk (2004). Samples were mercerised standard way. Cationization using 3-chlor-2-hydroxy-propyl-trimetyl-ammonium chloride (CHPTAC) was carried out during mercerisation, GrancariC, Tarbuk and DekaniC (2004). Raw and pretreated cotton knit samples were treated with the optical brightener Uvitex BHT (Ciba) in a wide concentration range (0.06% V 6%) and treated with 0,5 % of UV absorber Tinofast CEL (Ciba).

Relative intensity of fluorescence was measured on Spekol (Carl Zeiss, Jena) device adapted to measuring fluorescence in relation to the standard (Fluorescence Reference Standard, Datacolor). CIE whiteness and yellowness were measured using spectrophotometer Datacolor SF 600 PLUS-CT and UPF values using transmission spectrophotometer Varian Cary 50 Solarscreen according Australian/New Zeland Standard AS/NZS 4399:1996. Air permeability was measuerd according DIN 53 887.

3. RESULTS AND DISCUSION

The paper investigates the fluorescence of sunprotected white cotton fabrics after preparatory finish, optical bleaching and treating fabric with an ultraviolet protective agent, Tinofast CEL. Fabric weigth (mk), air permeability, relative intensity of fluorescence (frel), degree of whiteness (WB), yellowness index (YI) and UV protection factor (UPF) were determined.

As shown in Table 2, the weight and air permeability values indicate the high shrinkage of mercerised and cationized fabrics. Weaker transmission of UV light through a more tight knitted fabric increases UPF to maximum values of 1000 (Table 3).

The relative intensity of fluorescence (frel) of untreated and treated knitted fabrics with different FWAs concentrations, and with UV absorber are shown in Figure 1 a and b. The CIE whiteness for all samples is shown in Table 3. The relative intensity of fluorescence shown in Figure 1a and b indicate that the mercerised and catonized knitted fabrics give the highest fluorescence in the whole concentration range. They absorb the highest amount of the optical brightener compare to untreated and chemical bleached samples. Fabrics treated with UV absorber show the lower fluorescence than untreated ones. Mercerised and catonized fabrics show the highest fluorescence in all cases.

Figure 1. The relative fluorescence intensity of cotton fabric treated with a. FWA and b. FWA and UV absorber vs. FWAs concentration

One more phenomenon can be seen in Figure 1 and in Table 3. Increasing the FWAs concentration higher than optimal one decrease the intensity of the fluorescence. It is result of well known bathochromic shift of the remission spectrum. As well CIE whiteness is decreasing. The whiteness of the knitted fabric shown in Table 3 indicates that concentration of Uvitex BHT 1,2 % (o.w.f.) is the optimum one for this optical brightner.

The evaluation of the protection of the knitted fabric against UV radiation is shown in Table 4 by the UPF values according to AS/NZS 4399: 1996. Untreated knitted fabrics have relatively low UPF values. Cationized knitted fabrics have the maximum UPF value (UPF=1000), what means that cationization itself make excellent UV protection. Although expected, the samples of the highest fluorescence (�Xrel) and highest whiteness degree (WB) are not those having the highest UPF. It seems that knitted fabric tightness play a major role in this context as discussed above. For mercerized and cationized cotton knitted fabrics it is important that maximum UV protection doasn"St decrease after FWA and UV treatment.

4. CONCLUSION

In each wet treatment cotton swells what leads to shrinkage of knitted fabric. Shrinkage of knitted fabric increases its tightness, and a weaker transmission of UV radiation through tighter fabrics is the reason for their better protection against UV rays.

By increasing the concentration of optical brightener the intensity of fluorescence rises, whereas whiteness decrease. The fabrics that show the highest fluorescence and whiteness do not show, at the same time, the highest UPF values. Optical brightener insures high protection against UV radiation in cotton fabrics. By treating the optically bleached cotton with an UV protective agent in low concentration range of optical brightener, the synergetic effect of both agents on UV protection is observed, while at high concentrations of optical brighteners an antagonistic action is provoked causing reduced UPF-values.

Maximum UV protection of cotton knitted fabrics accomplished during processes of mercerization and cationization does not drop after optical bleaching or ultraviolet protection.



REFERENCES

Gies, P.H. et al. 1998. Clothing and Protection Against Solar UVR: Current Status. Jour. of the Home Economics Institute of Australia 5 (2): Sunsmart Supplement S8-S11, http://www.arpansa.gov.au

GrancariC A.M. and I. SoljaCiC (1980). Einflus der Konzentration optischer Aufheller auf Fluorescenz und Weissgrad von Baumwollgeweben. Melliand Textilberichte 61:242-246.

GrancariC A.M., A. Tarbuk and T. DekaniC 2004. Electropositive Cotton. Tekstil 50 (2): 55-62.

GrancariC A.M., T. PuSiC and A. Tarbuk 2004. Enzymatic Scouring for Better Textile Properties. In 3rd INTB Conference 2004, Book of Abstracts, ed. by S. Heumann. Graz: Univ. of Technology, P18.

Menter J.M. and K.L. Hatch 2003. Clothing as Solar Radiation Protection, Basel: Karger.

Neves J. and M. Neves 2003. Ultraviolet Protection Factor. In 3rd AUTEX Conference, Book of Papers, Gdansk: Technical University of Lodz, 229.

Shenai V.A. 1999. Fabric Whitening, Colourage, Annual: 63 - 81.

About the author:

Address: Ana Marija GarncariC, Faculty of Textile Technology,
University of Zagreb, Pierottijeva 6, 10000 Zagreb, Croatia
E-mail: amgranca@ttf.hr, tpusic@ttf.hr, anita.tarbuk@ttf.hr

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