1. Ultraviolet Protection for Knitwear Fabric
Jimmy Lam, Polly Chiu
Institute of Textiles & Clothing
The Hong Kong Polytechnic University 1

2. 21-23 June 2010 Vilnius, Lithuania
Outlines
Introduction and Background
Experimental Details
UV Transmission Test
Test Method
Knitted Fabric Test
Results and Discussions
Group A: Single Knit
Group B & C : Single Knit
Group D: Double Knit
Conclusions
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3. Introduction & Backgrounds
Textile materials and clothing have been used since antiquity by human beings for the purpose of protection, comfort and adornment.
But there were not much concern on how clothing protect us against skin cancer caused by excessive exposure to solar UVR until nowadays, since people are increasing their emphasis on health and environmental protection in today’s world.
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4. 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 9th most common cancer in Hong Kong in 2006; while there were 624 new cases
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Table 1: epidemiology of melanomas in different countries in 2003 HK UK
USA
Australia
Male/Female ratio
1: 0.71
1:1.14
1:0.64
1:0.65
Incidence rate*
0.5 13
16.2
46.9
Incidence relative to that of HK 1 26
32.4
93.8
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6. Benefits to Textiles and Clothing Industries
The Hong Kong Observatory introduced the measurement of solar UV Index in Hong Kong since 1999 and presents the results of statistical analysis on the daily and hourly UV Indices.
The relationship between UV index and exposure level is shown in Table 2.
The distribution of UV index and exposure level from 1999 to 2009 is summarized in Table 3.
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7. Benefits to Textiles and Clothing Industries
Table 2: UV Index and Exposure Level
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8. Benefits to Textiles and Clothing Industries
Table 3: Frequency Distribution (number of days and percentage) of Daily Maximum UV Index in Different Exposure Categories and Months (1 August July 2009)
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9. Benefits to Textiles and Clothing Industries
From Table 2, it could conclude that the UV exposure level in Hong Kong is always in the categories from “Moderate” to “Extreme”.
In accordance with WHO’s advice, with UV exposure level greater than 3, sun protection is required.
Therefore, there is a need in Hong Kong to design and engineer lightweight knitwear fabrics with UV protection function in regard to various Hong Kong’s whole year weather situation.
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10. 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
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11. Experimental Details 11

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UV Transmission Test
UV transmission measurement was one of the most important tests in this project.
There were several UV testing standards in the textile industry: Australia/ New Zealand standard; USA standard and British & European standards.
Each standard test method used its own defined set of data for calculation and required different test conditions.
In this project, the UV blocking test was in reference to the Australia/ New Zealand Standard: AS/NZS 4399:1966 “Sun Protective Clothing-Evaluation and Classification”. It is because this standard was one of the most commonly used standard.
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13. Australia/ New Zealand
Table 4: A brief comparison of different clothing standards for UV blocking testing
Country
Australia/ New Zealand
USA
British & European
Standard number
AS/NZS 4399:1996
AATCC 183:1998
BS 7914:1998
Results expression
All three standards report results as UPF rating
Calculation method
Calculate 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 condition
Not 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
Samples required
4 samples test required
6 samples test required
Samples state
Only 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 )
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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 1/20th 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:
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Knitted Fabric Test
Five groups of knitted fabrics were produced on three different gauges circular knitting machine using both cotton and coolmax yarn.
Both single knit and double knit structures were produced with different tightness in order to evaluate the degree of knitted fabric porosity to UV protection.
A detail of these five groups of fabrics is shown in Table 5.
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Table 5: Experimental Knitted Fabrics on Single Knit and Double Knit Production
Fabric
Fabric type
Machine
Gauge
Material
Yarn count
Knitting structure
Group A
Single Knit
SJE Jumberca
22G
Cotton
32Ne
Jersey (all knit)
Lacoste (knit+tuck)
Jacquard (knit+miss)
Group B
DXC Fukuhara
20G
Group C
Coolmax
30Ne
Group D
Double Knit
Albi
16G
1X1 rib (all knit);
Full milano (knit+miss);
Full cardigan (knit+tuck);
Interlock
Group E
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Two different loop lengths (fabric tightness) were produced for each group of fabric and each fabric group has different knitting sturctures.
Details of different knitting structures are shown in Table 6.
As different knitting structures will affect the openness of the knitted loop, which in turn will affect the degree of UV protection for different type of knitted fabric.
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Table 6: Fabric Structures
Fabric type
Knit Stitch
Fabric structure
Single Knit
All Knit
Knit and Tuck
Knit+tuck+miss
Jersey (Plain)
Lacoste
Jacqaurd
Double Knit
Knit+ miss
Knit+Tuck
All Knit (interlock)
1X1 rib
Full milano
Full cardigan
Interlock
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19. Results and Discussions19

20. Group A: Single Knit Fabric
Figure 1 shows the results of UPF protection for different stitches of single knit fabric with two different knitting tensions.
The effect of tightness (loose knitted fabric vs tight knitted fabric) has little effect on UV protection. However, different knitting structures will affect the UV protection properties.
The jacquard fabric (knit+tuck+miss stitches) has the highest UV protection than jersey (all knit) fabric. The lacoste (knit+tuck) has the lowest UV protection.
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Figure 1: UPF rating on single knit cotton fabric with different knitting structures
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22. Group B & C Fabric Single Knit
Both Group B and C were produced on the DXC Fukuhara circular knitting machine with two different materials.
Group B was pure cotton yarn and Group C was coolmax yarn.
The average UPF for these two different materials are shown in Fig. 2.
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Figure 2: UPF rating on single knit fabrics using cotton and coolmax yarns
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It can be shown in Figure 2 that coolmax yarn has a higher UV rating than cotton yarn.
The UV rating is significantly higher on tightly knitted fabric than loosely knitted fabric.
For both cotton and coolmax fabrics, the UV rating is higher on plain knitted (all knit) structure than lacoste (knit and tuck) structures.
This can be explained in term of open structure of tuck stitch. Tuck stitch will make the fabric wider which in turn will increase the knitted loop porosity and decrease the UV protection,
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25. Group D & E Double Knit Fabrics
Group D and E fabrics were produced on Albi Cylinder and Dial circular double knit machine.
Group D was made by pure cotton yarn and group E was made by coolmax yarn.
Three different double knit structures were produced, namely 1X1 rib (all knit); Full Milano Rib (Knit+Miss) and Full Cardigan Rib (Knit+Tuck).
Results were shown in Figure 3.
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Figure 3: UPF rating on double knit structures by cotton and coolmax yarn
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Figure 6 Two courses repeat of interlock fabric
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Figure 5: UPF rating on interlock fabric and rib fabrics
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Conclusions
An engineering approach of the knitted fabric porosity to UV protection in terms different stitches (Knit, Tuck and Miss stitches) and fibres (cotton and Coolmax) were studied.
For the single knit structures, jacquard fabric (knit and miss stitches) has the highest UPF rating, followed by plain fabric (knit stitch) and lacoste fabric (knit and tuck stitch).
For the double knit fabrics, the highest UPF rating is interlock fabric, followed by full milano rib, 1X1 rib and the full cardigan rib gives the lowest UPF rating. These can be explained by different knit, tuck and miss stitches which will affect the porosity of knitted fabric. Tuck stitch shows the highest porosity in the fabric and followed by knit stitch and miss stitch.
For all the knitting structures, double knit fabrics give higher UV rating than single knit fabrics. Coolmax yarn gives a higher UV rating than cotton yarn.
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Acknowledgement
The authors would like to acknowledge the funding supports from the Central Research Grant (A-AS21) from the Hong Kong Polytechnic University.
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