Engineering Approach on Knitwear Fabric for Ultraviolet Protection Polly Chiu, Jimmy Lam Institute of Textiles & Clothing The Hong Kong Polytechnic University

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Outlines Introduction and Background Experimental Details –Tightness factor –Knitting structures –UV transmission test Results and Discussions –Effect of tightness factor to UPF –Effect of knitting structures (single and double knit) to UPF Conclusions

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Introduction & Backgrounds Textile materials and clothing have been used since antiquity by human beings for the purpose of protection, comfort and adornment. Recent times have witnessed a steadily increasing emphasis on the role that clothing can play guard against skin cancer and in particular malignant melanoma caused by excessive exposure to ultraviolet solar radiant energy.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Introduction & Backgrounds According to the World Health Organization (WHO), recent statistics shown that the number of people died from skin cancer each year is increasing; while the Australian statistics represent the highest incidence of skin cancer world-wide. In Australia, over one thousand people died from skin cancer annually and there are approximately 270,000 new cases of skin cancer diagnosed per year. Skin cancer became one of the top 10 cancers in Hong Kong for the first time in 2002, and then it ranked as the 9 th most common cancer in Hong Kong in 2006; while there were 624 new cases

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan HKUKUSAAustralia Male/Female ratio1: 0.711:1.141:0.641:0.65 Incidence rate* Incidence relative to that of HK Table 1: epidemiology of melanomas in different countries in 2003

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Introduction and background Despite the importance of protection afforded by textile fabrics against ultraviolet radiation, there are few systematic studies on the interaction between the structure and physical properties of the textile materials to UV protection especially on summer lightweight knitted fabric. However, it is believed that fabric cover factor, has a direct influence on the fabric ultraviolet protection factor [2]. The most important fabric properties in this context are: tightness factor, fibre type, yarn construction, fabric construction, finishing processes, colour, UV absorbers, wash and wear, fabric stretch and wetting [3-6]. In this research project, textile engineering approach was applied and the effect of tightness formed by different knitting tensions on UPF was examined

Experimental Details

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Tightness Factor Two experiments were conducted to investigate the effect of UV protection of knitted fabric in terms of the following: 1.The effect of different tightness/ loop lengths of plain knitted fabric to UV blocking, and 2.To study the effects of different knitting structures, tightness, washing and dyeing to UV blocking.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Knitting Structures Two set of commercial knitted samples were used for the first experiment, which were of two different machine gauges, 5G and 12G with three different loop lengths (tightness) of loose, normal and tight stitch. For the second experiment, seven set of knitted fabrics with different structures were prepared in the laboratory namely 1) single knit plain fabric; 2) single knit and tuck fabric; 3) single knit, tuck and miss fabric; 4) double knit 1X1 rib fabric; 5) double knit interlock fabric; 6) double knit full cardigan fabric and 7) double knit full Milano fabric.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Test Method In this research, protection factor (PF) was used for comparison and analysis because it is useful to quantify the UVR protection by fabric. PF indicates how much UVR is blocked by a textile material. For instance, a material with a UVR falling on PF rating of 20 would allow 1/20 th of UVR falling on its surface to pass through it; which means that it would block 95% of the UVR and transmit only 10%. The following equation is used to calculate PF:

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan UV transmission test CountryAustralia/ New Zealand USA British & European Standard numberAS/NZS 4399:1996AATCC 183:1998BS 7914:1998 Results expressionAll three standards report results as UPF rating Calculation methodCalculate mean UPF value and average of UVA & UVB transmission, to classify UPF level Similar to AS/NZS 4399:1996 Calculate the erythemally effective penetration (P): P=1/UPF Testing conditionNot specify any conditioning, normally 20  5  C and 50  20% relative humidity (RH) Require sample conditioning of 21  1  C and 65  2% RH for at least 4 hours Require sample conditioning of 20  2  C and 65  2% RH for at least 16 hours Wavelength range nm nm nm Samples required4 samples test required 6 samples test required 4 samples test required Samples stateOnly specifies testing in dry and relaxed state Provide measurements of wet and/or stretched samples Provide measurements of wet and/or stretched samples for European standard (EN )

Results and Discussions

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Effect of Tightness Factor to UPF Knitted fabric is formed by a yarn travels across the fabric inter-looping with a loop in the previously formed row, knitted fabric generally has greater openness than woven fabric due to the formation of loops. Therefore, fabric tightness factor was predicted to be an important factor affecting UPF. In this experiment, commercially knitted fabric of two different gauges (5G and 12G) was knitted with three different knitting tensions (tight, normal and loose) and the results are shown in Table 1

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan MaterialCombed cotton Machine Gauge5G12G Knitting StructureSingle jersey plain knit Knitting Tension1-3/8” (Tight) 1-4/8” (Normal)1-5/8” (Loose)1-3/8” (Tight)1-4/8” (Normal)1-5/8” (Loose) Yarn Tex Fabric Density (courses per 10cm) Fabric Density (wales per 10cm) Stitch Density (per sq. cm) Loop length (per 1 stitch) Fabric Weight (g/sq. m) Tightness Factor Fabric thickness (mm) Mean UPF Calculated UPF UVA Transmission(%) UVB Transmission(%) UVR Transmission(%) Difference of UPF between tight and loose (%) Tabe 1 Different cover factors on UPF values

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Effect of Tightness Factor Table 1 showed that higher tightness factor provided greater UV protection for both machine gauges. For the 5G samples, tightness factor for loosely and tightly knitted fabrics increased from 1.37 to 1.57; which the mean UPF increased from to respectively. The percentage of difference in mean UPF was % with tightness factor changed by 14.6%. The results showed a same trend with 12G samples, but a smaller percentage of difference in mean UPF was obtained. The percentage difference in mean UPF of 12G samples was 51.36% with 10.24% change in tightness factor.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Effect of Tightness Factor The results indicate fabrics with higher tightness will give greater UV protection. Therefore, it is possible that fabrics with higher tightness, and also higher density, have smaller micropores which provide less free space for UV radiation to pass through the fabric and resulted in higher UV protection. Figure 1 and 2 show the effect of fabric tightness to UV transmission for both 5G and 12G fabrics respectively

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Figure 1: Effect of tightness of 5G samples On UV transmission

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Figure 2: Effect of tightness of 12G samples On UV transmission

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Effect of Knitting Structures Single Knit Structures Three single knit structures of plain fabric, knit and miss fabric and knit, tuck and miss fabric were prepared by Stoll machine using 2x20Ne 100% cotton yarn and the results are shown in Table 2.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Single knit Knitting Structure single jersey plain knitknit and tuckknit, tuck & miss Knitting Tension TightNormallooseTightNormallooseTightNormalloose Fabric thickness Mean UPF Calculated UPF UVA Transmission( %) UVB Transmission( %) UVR Transmission( %) Table 2 Results of single knit structures on UPF

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Single Knit Structures The three single knit structures showed a similar but relatively low average mean UPF value of Knit and tuck structure provided the lowest UV protection among the 3 structures, whereas the knit, tuck and miss structure provided the highest UV protection. Figure 3 shows the openness of different knit, tuck and miss stitches.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Figure 3: Effect of Knit, Tuck and Miss Stitches on UV transmission KNIT MISS TUCK

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Effect of Tuck Stitch A tuck stitch is formed by feeding a new yarn to the needle which the old loop remains around the latch and stays open. The tuck needle didn’t clear the old loop due to its intermediate rising position. A tuck loop has a shape like an inverted “V” which will form a wider, shorter and thicker fabric than plain knit alone. Hence, fabrics with tuck loops would have a more open work effect; and this contributed to the increased free spaces for UV radiation to pass through the fabric and lower its UV protection.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Effect of Miss Stitch Miss stitch, contributed differently than tuck stitch. A miss loop is also called the float or welt. It is formed as the needle does not rise up during yarn feeding, and it appears as a short length of horizontal yarn at the back of the fabric. It will form a narrower and higher density fabric than plain knit. And the fabric will be thicker and heavier if larger numbers of miss yarns are used. Therefore, fabric with miss stitches has higher density which will reduce free space for UV radiation to pass through the fabric; and this helped to increase UV protection.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Double Knit Structures Four double knit structures of 1x1 rib, interlock, full cardigan and full Milano were prepared Results are shown in Table 3.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Table 3 Results of double knit structures on UPF

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Double Knit Structures Comparing the four structures of double knit to single knits, all of them provided a significantly stronger UV protection than single knits. Double knit structures have relatively higher average mean UPF values of 24.81, except for full cardigan which was UV protection increased from full cardigan to 1x1 Rib, and then to full Milano, where interlock offered the greatest UV protection among the 4 double knit structures. The results matched with the knitting science in terms of the properties of knitted loops.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Double Knit Structures Double knit can be classified as a fabric knitted by two sets of needles of the machine or by at least two needle beds. It is different from single knitted fabric by which single knitted fabric is produced by using only one set of needles. Therefore, double knitted fabrics are generally formed with more materials (i.e. one more set of yarns) than single knits; which is believed as one of the factors contributed to higher UV protection as larger amount of fiber per unit area resulted in better UV protection since more fibers were present to block or absorb solar UV radiation.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Double Knit Structures: Cardigan Since the UV protection ability increased in ascending order as: full cardigan, 1x1 Rib, full milano and interlock; it implied that knitting structure was obviously an important factor affecting UPF. Full cardigan contains no rib courses but two courses of knit & tuck with alternatively in direction; and has identical face and back sides. The tuck stitches, as discussed in the previous part concerning single knit, made the fabric wider and shorter which lowers its UV protection. Therefore, unwashed full cardigan samples had a relatively low average mean UPF value of 7.22, 5.36 and 4.96 for tight, normal and loose knit respectively.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Double Knit Structures: Milano Full milano is different from full cardigan by composing of knit & miss stitches only. No tuck stitch is involved in milano structures. Its fabric structure is three courses per repeat. The first course is a rib course, and the second and third courses are one knit in front and one knit in back plain courses. It provides a narrower and higher density fabric with regard to miss stitches, which offers a better UV protection than full cardigan. The average mean UPF values for tight, normal and loose knits were 47.49, and respectively.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Double Knit Structures: Interlock Interlock is of a different group than rib for double knit structures. Interlock gating involves 2 sets of needles facing each other exactly on the same line. Interlock fabric is formed by two courses of 1x1 Rib meshed with each other, so it can be described as a double 1x1 Rib. Interlock has a close surface structure with both sides identical with face loops. Therefore, it provided the greatest UV protection among the double knits because it has a close structure, with more materials per unit area and hence thicker. The average mean UPF values were 29.85, and for tight, normal and loose knits.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Conclusions Textile fabric can be engineered to reduce the harmful UV radiation. Experiments show that for the knitted fabrics, tightness factor can be used to control the degree of openness of the knitted fabric. The tighter the knitted fabric, the smaller is the opening of the fabric, and the lower of UV transmission through the fabric. Double knit structures show a higher UV protection than single knit structures because double knit fabrics have more materials per unit area and closer structure, resulted in significantly highly UPF than single knits. Interlock structure shows the highest UV protection, follows by full Milano, 1x1 rib and full cardigan.

The 38th TextileResearch Symposium at Mt. Fuji, Sept , Japan Acknowledgement The authors would like to acknowledge the funding supports from the Central Research Grant (A-AS21) from the Hong Kong Polytechnic University.