Effect of Stretching on UV protection of Knitted Fabrics Presenter: Dr. Jimmy K.C. Lam Wai-yin Wong...
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Transcript of Effect of Stretching on UV protection of Knitted Fabrics Presenter: Dr. Jimmy K.C. Lam Wai-yin Wong...
Effect of Stretching on UV
protection of Knitted Fabrics
Presenter: Dr. Jimmy K.C. Lam
Wai-yin Wong & Jimmy K.C. Lam*
2
OVERVIEW
1. Introduction
2. Significance
3. Ultraviolet Radiation
4. Assessment of UV protection of textiles
5. Main Factors affecting UV protection of textiles
6. Stretch (Tension)
7. Methodology
8. Results
9. Conclusion
10. Future Works
11. Acknowledgement
12. References
3
1. INTRODUCTION
Increasing number of people dying from skin cancer each year over
the world and over-exposure to ultraviolet radiation (UVR) deemed to
be one of the main reasons1
Clothing is recommended by physicians and medical experts as
one of the primary methods of protecting the skin form the harmful
UVR2-3
Clothing offers more durable protection against the deleterious
impacts of UVR than sunscreen
Limited protection against UVR is usually enhanced by chemical
approach with UV-absorbers (e.g. TiO2, ZnO)
Knitted fabrics are more porous and elastic than woven fabrics,
UV protection of knitwear enhanced by chemical is only sufficient when
the fabric structure is closed enough
4
Skin is our biggest organ of the body
Clothing has the ability to absorb, reflect, or scatter radiant energy
thereby it can be considered as a kind of wearable sunscreen
which is essential and suitable to everyone
Fabric construction offers the simplest and healthiest
solution to achieve good UV protection without additional
finishing processes
Highly beneficial to those having extreme sensitivity to sunlight,
living in sunlight-intensive regions and for those with outdoor
occupations
Extensive exposure to UVR at the age between 10 and 24 has been
identified as a potent risk factor in developing skin cancer4
Worth to develop children’s UV-protective clothing
2. SIGNIFICANCE
5
Electromagnetic radiation consisting visible light (50%), infrared
radiation (45%) and UVR (5%)
Essential for our well-being (synthesis of vitamin D, for growth and
maintenance of a healthy skeleton)
Depletion of stratospheric ozone layer is a serious environmental
problems
Decrease of 1% in ozone lead to increases in UVR at Earth’s surface
and may eventually lead to a 2.3% increase in the rate of skin
cancer5
3. ULTRAVIOLET RADIATION
6
4. ASSESSMENT OF UV PROTECTION OF TEXTILES
(1) In vivo measures the minimum erythema dose (MED) (minimum quantity of
radiant energy required to produce first detectable reddening of skin, 22±2 hours after exposure) of UVR using human skin as a test indicator
tests the ability of a fabric to protect against sunburn with measurement of MEDs on the skin protected and unprotected by a fabric
SPF is the ratio of the time of solar radiation exposure required for the skin to show redness with and without protection by fabric6-7
Pro: gives the direct response of the human body to UVRCon: it is difficult to conduct it as a standard test method because it
involves human subjects (ethical issue) and relies on the optical measurement techniques to count the MED
7
(2) In vitro Simpler, less time consuming, more reliable, widely adopted
UV protection ability of fabrics is expressed as Ultraviolet Protection Factor (UPF)
Measure UVR transmittance through a fabric over UV spectrum (290-400 nm)
A spectrophotometer equipped with an integrating sphere is used to measure
the UVR transmittance and UPF is calculated from the ratio of the average UVR
transmitted through air to the average UVR transmitted though the fabric8
Calculated UPF value is rounded into a multiple of 5 (from 5+ to 500+) and
UPF>50 are generally indicated as 50+
Although definition of UVR given in the international standards start at 280 nm,
UVR irradiance at wavelengths below 290 nm is not used in the calculation of UPF
because these wavelengths are unlikely to reach the earth surface9
8
Australian/New Zealand standard (AS/NZS 4399:1996)9
Using a solar spectrum measured in Melbourne
Measures UPF of fabric in dry and tensionless (un-stretched)
state
At least 4 specimens tested (2 from machine direction and 2 from
cross machine direction)
UPF 20 ~ allow 1/20th of UVR falling on its surface to pass through it;
which means that it would reduce UVR exposure by a factor of 20
For the purposes of labeling, sun protective clothing shall be
categorized according to its rated UPF
A textile product must have a minimum UPF of 15 to be rated as UV
protective
UPF RatingUVR Protection
CategoryEffective UVR
transmission (%)UPF Rating
15 – 24 Good Protection 6.7 – 4.2 15, 20
25 – 39 Very Good Protection 4.1 – 2.6 25, 30, 35
40 – 50, 50+ Excellent Protection ≦2.5 40, 45, 50, 50+
9
5. MAIN FACTORS AFFECTING UV PROTECTION OF TEXTILES
Fiber Types
Fabric Construction and Yarn properties
Dye characteristics (Color)
Additives and Nanotechnology
Moisture content (Wetness)
Stretch (Tension)
End-use conditions (Wash and wear)
10
6. Stretch (Tension)
Stretching is a common end-use conditions
Knitwear fabric is easily deformed or stretched
Stretching a fabric will normally cause ↓UPF:
Open up spaces in fabrics & alter fabric structure
↑Porosity accompanied by a decrease in fabric thickness
Knitted fabrics construction changed in openness/closeness more
than woven fabrics
Yarns in knitted fabrics have a greater freedom of movement
11
Moon and Pailthorpe (1995) found there is 15.5% of elongation in
average of elastane garments worn and caused a remarkable
reduction of UPF.10 Measurements of elongations were measured on body
part expecting to have a high incidence of skin cancer
Kimlin et al. (1999) also studied effect of stretch of stocking against UVR
transmission11
Clark et al. (2000) investigated the effects of areal and linear stretches12
Osterwalder et al. (2000) also found increase of UVR penetration is
almost linear with stretch.13 The relationship between stretch and
UVR penetration (%) is illustrated.
12
UPF label of garment may not reflect actual UV protection in
a wearing situationis as fabric is measured in a relaxed state
Limited research on UV protection of knitted fabrics with
different structures
Aim: Investigate impact of stretching on UV protection of
bleached single and double knitted cotton fabrics constructed with
different knit structures
13
7. METHODOLOGY
Materials Stoll CMS 822 14G computer flat knitting machine 100% cotton yarn with yarn count 3/40s Bleached fabric specimen 10 knit structures
14
Weft knitted fabrics (stitches)
Knit stitch: formed by needle receives new
loop and knock–over the old loop that held from
the previous knitting cycle
Tuck stitch: formed when needle reaches to a
height during rising that the old loop is not
cleared but the needle hook catch a new yarn
during downloading movement
Miss stitch: formed at the height that neither
the old loop is cleared nor needle hook can
catch new yarn during downloading movement
15
UPF Measurement
Ultraviolet Protection Factor (UPF) of fabric specimens was measured by
Cary 300 Conc UV-Vis spectrophotometer (In-vitro method)
Australian/New Zealand Standard AS/NZS 4399:1996
Dry, flat and tensionless state (un-stretched)
Both machine and cross-machine directions (Wale and course directions)
Linear stretch (stretch in one direction only) by 15% elongation from its
original un-stretch state
UPF= 𝐸𝑒𝑓𝑓𝐸′= σ 𝐸λ × 𝑆λ × ∆λ400nm290nmσ 𝐸λ
400nm290nm × 𝑆λ × 𝑇λ × ∆λ
16
8. RESULTS
3.1 Effect of stretching on UPF of bleached single knitted cotton fabrics
All Knit Knit + Tuck Knit + Miss (25%)
Knit + Miss (50%)
0
5
10
15
20
25
13.8 12.4
13.9
19.7
10.8
7.6 9.4
14.3
8.1 7.7 9.8
13.4
Impact of stretch on UPF of bleached single knit-ted cotton fabrics
Un-stretch Stretch-Vertical Stretch-Horizontal
Single Knit Structures
UP
F
Significant difference in UPF between fabrics in un-stretch state and fabrics stretched
in vertical and horizontal directions (F2, 69 = 24.28, p ≤ 0.05)
No significant difference in UPF between fabrics stretched in vertical and
horizontal directions (p = 0.616)
All the single knitted cotton fabrics here cannot be rated as UV protection (minimum
UPF 15) and the situation is even worse after stretching
17
Resulted UPF in both stretching directions are averaged for
further calculation of reduction in UPF (%) of fabrics
Reductions in UPF (%) by stretching for the four single knit structures
are listed in table:
The reduction in UPF of Knit & Tuck fabrics are the highest (38.6%)
Other three single knit structures have similar reductions in UPF by
stretching (range of reduction in UPF: 29.5 - 31.4%)
Fabrics with tuck stitches have worse UV protection not only in un-
stretch state but also in the stretched state with higher reduction in
UPF (%) than the other three single knit structures
Single Knit Structures
Reduction in UPF (%)
Stretched-Vertically Stretched-Horizontally AverageAll Knit 21.6 41.1 31.4Knit & Tuck 39.1 38.1 38.6Knit & Miss (25%) 32.6 29.4 31.0Knit & Miss (50%) 27.3 31.6 29.5
18
3.2 Effect of stretching on UPF of bleached double knitted cotton
fabrics
1x1 Rib Half Cardigan Full Cardigan Half Milano Full Milano Interlock05
101520253035404550
21.2
12.8 14.2
28.9 29.4
45.0
17.9
7.8 7.8
22.3 21.6
30.3
11.2 10.6 9.5
17.7 20.1
29.2
Impact of stretch on UPF of bleached double knitted cotton fabrics
Un-stretch Stretch-Vertical Stretch-Horizontal
Double Knit Structures
UP
F
All the double knit structures experienced significant reductions when the fabrics
were either stretched in vertical or horizontal directions (F2, 105 = 9.636, p ≤ 0.05)
No significant difference in UPF between fabrics stretched
in vertical and horizontal directions (p = 0.749)
19
Double knitted fabrics have better UV protection than the single
knitted fabrics in both un-stretch & stretched states
The reduction in UPF of Full Cardigan is the highest (39.2%) while
the other five double knit structures have similar reductions in UPF
by stretching (range of reduction in UPF: 28-33.8%)
Full Cardigan has the highest proportion of tuck loops among the six
double knit structures
A tuck loop tends to extend wider than a knit loop which increases the
fabric width and thus more UV radiation can be transmitted
Double Knit Structures
Reduction in UPF (%)
Stretched-Vertically Stretched-Horizontally Average1x1 Rib 15.8 47.0 31.4 Half Cardigan 38.9 17.0 28.0 Full Cardigan 45.1 33.4 39.2 Half Milano 22.6 38.8 30.7 Full Milano 26.7 31.6 29.1 Interlock 32.6 35.1 33.8
20
9. CONCLUSION
Both the bleached single knitted and double knitted cotton exhibit a
significant reduction of 30-40% in UPF when stretched by 15% linear
directions
Vertical and horizontal stretching give similar reductions in UPF
Bleached single knitted cotton fabrics cannot be rated as UV protective
(minimum UPF 15) in the un-stretch state and the situation get worse when
the fabrics were stretched
Bleached double knitted fabrics retain to be UV protective even if they are
stretch by 15% in linear direction
Fabrics with miss loops and the Interlock structure retain UV protective ability
when the fabric is stretched
Knit & Tuck structure (single knit) and Full Cardigan (double knit with tuck
loops) exhibited the highest reduction in UPF
Fabrics with tuck loops are not recommended for UV protective knitwear
21
10. FUTURE WORKS
Stretching in different percentages (e.g. 5%, 10%, 15%, 20%) of
elongation
Stretching and wetting simultaneously
Stretching colored fabrics, different materials (e.g. elastane added
fabrics)
Improvement on the stretching apparatus
Standardized method for measurement of UPF of a stretched fabric
in the future
22
The research is funded in part by the General Research Fund (A-SA21) from the University Grants Committee, Hong Kong and The Hong Kong Polytechnic University, Hong Kong.
11. ACKNOWLEDGEMENT
23
12. REFERENCES1. Ultraviolet radiation and human health (2009). Retrieved May 10, 2011 from
http://www.who.int/mediacentre/factsheets/fs305/en/index.html2. Hurwitz, S. (1988). The Sun and sun protection: recommendations for children. Journal of
Dermatologic Surgery and Oncology, 14(6), 687-680.3. Hacker, S.M., Browder, J.F. and Ramoscaro, F.A. (1993). Basal-cell carinoma – choosing the best
method of treatment for a particular lesion.2. Postgraduate Medicine, 93(8), 101-111.4. Capjack, L., Kerr, N., Davis, S., Fedosejevs, R., Hatch, K.L. and Markee, N.L. (1994). Protection of
humans from ultraviolet radiation through the use of textiles: a review. Family and consumer sciences research journal, 23(2), 198-218.
5. Roy, C.R., Gies, H.P., and Toomey, S. (1995). The Solar UV Radiation Environment: Measurement Techniques and Results. Journal of Photochemisty and Photobiology. B, Biology, 31(1-2), 21-27.
6. Menter, J.M. and Hatch, K.L. (2003). Clothing as solar radiation protection. Current Problem in Dermatology, 31, 50-63.
7. The American Society for Testing and Materials, ASTM D6544-2011, Standard Practice for Preparation of Textiles Prior to Ultraviolet (UV) Transmission Testing.
8. Gies, H.P., Roy, CR., Elliot, G. and Wang, Z. (1994). Ultraviolet radiation factors for clothing. Health Physics, 67(2), 131-139.
9. Australian/New Zealand Standard, AS/NZS 4399:1996, Sun protection clothing – Evaluation and classification.
10. Moon, R. and Pailthorpe, M. (1995). Effect of Stretch and Wetting on the UPF of Elastane Fabrics. Australasian Textiles, 15(5), 39-42.
11. Kimlin, M.G., Parisi, A.V. and Meldrum, L.R. (1999). Effect of stretch on the ultraviolet spectral transmission of one type of commonly used clothing. Photodermatology Photoimmunology Photomedicine, 15(5), 171-174.
12. Clark, I.E.S., Grainger, K.J.L., Agnew, J.L. and Driscoll, C.M.H. (2000). Clothing Protection Measurements. Radiation Protection Dosimetry, 91(1-3), 279-281.
13. Osterwalder, U., Schlenker, W., Rohwer, H., Martin, E. and Schuh, S. (2000). Facts and fiction on ultraviolet protection by clothing. Radiation Protection Dosimetry, 91(1-3), 255-260.