Textile Research Journal

2 downloads 0 Views 246KB Size Report
Clark, I. E. S., Grainger, K. J. L., Agnew, J. L., and Driscoll, C. M. H., Clothing .... Kullman, R. M. H., Clarence, O. G., and Ruppenicker, G. F.,. Air Permeability of ...
Textile Research Journal http://trj.sagepub.com

Ultraviolet Protection Factor of Gray-state Plain Cotton Knitted Fabrics Snezana B. Stankovic, Dusan Popovic, Goran B. Poparic and Mateja Bizjak Textile Research Journal 2009; 79; 1034 DOI: 10.1177/0040517508102016 The online version of this article can be found at: http://trj.sagepub.com/cgi/content/abstract/79/11/1034

Published by: http://www.sagepublications.com

Additional services and information for Textile Research Journal can be found at: Email Alerts: http://trj.sagepub.com/cgi/alerts Subscriptions: http://trj.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.co.uk/journalsPermissions.nav Citations http://trj.sagepub.com/cgi/content/refs/79/11/1034

Downloaded from http://trj.sagepub.com at KoBSON on July 1, 2010

Textile Research Journal

Article

Ultraviolet Protection Factor of Gray-state Plain Cotton Knitted Fabrics Snezana B. Stankovic1

Abstract

The protection provided by clothing against ultraviolet (UV) radiation has been the subject of considerable recent research. However, a lack of investigations concerned with the influence of yarn properties on UV protection capabilities of fabrics seems to be present. This study investigated the influence of yarn twist and surface geometry on these properties of fabrics. The gray-state plain cotton knitted fabrics were produced from yarn differing in twist level under controlled conditions, so as to obtain as similar as possible construction of the fabrics. These plain knitted (single jersey) fabrics were spectrophotometrically assessed and UV protection factor was calculated. The results obtained indicated that yarn twist to a great extent influenced the UV protection properties of the knitted fabrics through the influence on yarn compactness and surface properties, which in turn influenced the open porosity of the fabric. The results were also interpreted as the consequences of minimal differences between knitted fabrics’ construction (different stitch density), which could not be avoided because of the yarn twist differences.

Textile Engineering Department, Faculty of Technology and Metallurgy, University of Belgrade, 11120 Belgrade, Serbia

Dusan Popovic and Goran B. Poparic Faculty of Physics, University of Belgrade, 1100 Belgrade, Serbia

Mateja Bizjak Department of Textiles, Faculty of Natural Science and Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia

Key words

air permeability, hairiness, open porosity, plain cotton knitted fabric, twist, ultraviolet protection factor, yarn

The beneficial effects of human exposure to ultraviolet radiation (UVR) are well known. The main benefit is promoting the synthesis of vitamin D from precursors in the skin. Other beneficial effects of UVR are mainly therapeutic. However, prolonged and repeated, both occupational and recreational, sun exposure of the population causes some detrimental effects. The most obvious short-term effect of over-exposure to UVR is sunburn, also known as erythema. Chronic sun damage leads to skin photoaging and non-melanoma and melanoma skin cancer. The proportion of the UV region (100–400 nm) is about 5–6% of the total incident radiation and can be classified

Textile Research Journal Vol 79(11): 1034–1042 DOI: 10.1177/0040517508102016 Figure 1 appears in color online: http://trj.sagepub.com

by wavelength into three regions. Light radiation of wavelength 315–400 nm represents UVA region. UVB radiation is in the range of 280–315 nm [1]. The region below 280 nm is UVC radiation, which is extremely dangerous. Fortunately, UVC and some UVB radiation (100–290 nm) do not reach the earth’s surface due to absorption by the stratospheric ozone in the atmosphere.

1

Corresponding author: Textile Engineering Department, Faculty of Technology and Metallurgy, University of Belgrade, 11120 Belgrade, Serbia. e-mail: [email protected]

© The Author(s), 2009. Reprints and permissions: http://www.sagepub.co.uk/journalsPermissions.nav

Downloaded from http://trj.sagepub.com at KoBSON on July 1, 2010

Ultraviolet Protection Factor of Gray-state Plain Cotton Knitted Fabrics S. B. Stankovic et al. In Eastern and Southern Europe where the UV index can be as high as in Australia, it is of great interest for the population, especially for outdoor workers, children and adolescents, to protect themselves. In addition to the outdoor natural source of UVR, there are also interior artificial UVR sources such as different types of lamps for medical care and phototherapy, work places’ lightening, industrial arc welding, advertising lamps, etc. Obviously, UV exposure of people takes place in their work and leisure places, homes and outdoors. Therefore, the UVR protection provided by clothes becomes a subject of considerable interest. There are several possible pathways for UV light distribution when UVR reaches textile fabric. UVR can be reflected, absorbed and transmitted by fabric. Part of the radiation is absorbed by the fibers, i.e. it is converted to a different energy form [2]. Another part of the radiation passes directly through the fabric via gaps between the fibers and yarns and this part is referred to as the ‘transmission’ [3]. Some radiation is reflected or scattered by the fibers, which may contribute to transmitted radiation if it is not absorbed by other fibers. It is clear that all clothing provides some degree of UV protection. Several factors determine the effectiveness of clothing at reducing UVR. In addition to clothing design [4, 5], the fabric properties affecting the UV transmission through clothing include composition (fiber type), construction (tightness of weave), weight and thickness [4, 6–11]. Color and other processing techniques (bleaching, usage of UV absorbers) can also affect clothing UVR blocking capabilities as well as other parameters relating to use and wear such as wetness, stretch, heat or chemical treatments [4, 12–22]. The interaction of these parameters (fiber, yarn, fabric, processing techniques and finishing treatments) additionally complicates the understanding of clothing behavior under UVR. However, it seems that fabric open porosity, which can be defined by a variety of terms, including cover factor, fabric tightness or fabric openness, and physico-chemical type of fiber are the key parameters influencing the UV protection ability [23–25]. Several studies have reported the effect of fiber chemistry on UV protection properties of textiles. It has been found that fibers containing conjugated aromatic system of polymer chains, such as polyester, are more effective in UV absorption [3, 7, 26]. Cellulose fibers (cotton, flax, viscose) have no double bonds in their chemical structure, thus have a low intrinsic UV absorption capacity providing relatively low UV protection properties of textile fabrics made thereof [3, 7]. However, natural pigments, pectin and waxes in natural cellulose fibers act as UV absorbers having a favorable effect on ultraviolet protection factor (UPF) of gray-state fabrics. Hustvedt and Cox Crews first reported a high UPF of naturally-pigmented cotton fabrics [21]. According to other authors’ findings, the majority of UVR transmission through textile fabrics occurs through the open spaces between yarns. This has

1035

been demonstrated by a reduction of the total area of pores between yarns in fabric after washing and the subsequent reduction of UV transmission, i.e. the increase in UPF measurements [13, 16, 17, 27]. Zampetakis and Dobnik Dubrovski investigated gray-state cotton woven fabrics varying in type of weave and relative fabric densities and found high correlation between the open porosity and UPF (r=0.973), which follows the power function [11]. Subsequently, the type of wave and fabric tightness (warpweft density, stitch density) were confirmed to have indirect connection with UPF through the influence on the openness of fabric structure [12]. Despite the fact that yarn structure can also influence the inter-yarn pores or the openness of fabric, there are very few investigations concerning the relationship between the structure of yarn and the fabric UV protection effectiveness [28–30]. The subject of those investigations was the influence of yarn linear density on UV protection ability of fabric, but there is no published research concerned with the UV transmission properties of fabrics related to yarn twist and surface properties. For our paper, the idea was to evaluate the effect of yarn twist (yarn core and surface geometry) on UV protection properties of plain cotton knitted fabrics. In consideration of the fact that the structure of fabric and constituent yarn would be changed by any finishing treatments (physico-mechanical or chemical), the investigation of UV protection ability of the cotton knitted fabrics was conducted in the gray state. In such a way, the influence of yarn twist on fabric behavior under UVR becomes clearer. In this investigation, an attempt was also made to evaluate the effect of yarn structure on UPF during use of fabrics (wet treatment).

Test Methods for Quantitative Assessment of Fabrics’ UV Protection There are two principal test methods for quantitative assessment of UV protection by clothing. In vivo testing on human subjects is based on the determination of the minimal erythema dose for a test subject with and without fabric. However, cost and ethical considerations are the limitations of the in vivo test methods. In vitro test method is based on determination of the UPF, defined as the ratio of the average effective UVR irradiance calculated for unprotected skin to the average effective UVR irradiance calculated for skin protected by the test fabric. Inter-comparison measurements of different testing laboratories have shown that spectrophotometric assessment of the UV transmission through fabrics is an accurate and reproducible test method for determining UPF [31]. This method

Downloaded from http://trj.sagepub.com at KoBSON on July 1, 2010

TRJ

TRJ

1036

Textile Research Journal 79(11)

Table 1 UPF ratings and protection categories by EN 13758-2:2003. Protection category

UPF range Rating

Excellent

Transmission, %

above 40

40+