Innovative Approaches to Enhance UV Protection in Knitted Fabrics: A Study

1. EXCO, Daegu, Korea Nov 1-4, 2011 The 11th Asian Textile Conference Presenter: Wong Wai Yin Dr. Jimmy Lam, Dr. C.W. Kan Influences of Knitted Fabric Construction & Color on Ultraviolet Protection

2. Overview • Introduction • Literature Review • Background • Previous Findings • Experimental Details • Results & Discussions • Conclusion • Future Study • References

3. Introduction • Increasing no. of people dying from skin cancer due to over exposure to UVR • Skin ageing, skin cancer, cataract, ↓Effectiveness ofimmune system • Excessive sun exposure in childhood is likely to contribute to skin cancer in later life • Clothing provide limited protection against UV radiation • Factors affecting UV protection of clothing: • Fiber Composition • Fabric Construction: tighter structure, smaller the fabric pores for UVR transmission • Yarn twist • Fabric Thickness, Weight • End-use conditions: Wetness / Stretching • Coloration: absorption band of dye extend into invisible UV region (290-400nm) • Chemical Treatments / Additives

4. Literature Review • Parameters affecting UV protection are well researched • Many studies have concentrated on: • Woven fabrics • Chemical approaches to enhance UV protection • UV absorbers: TiO2, ZnO, optical brightening agents • Little work has been done on: • Influence of knitted fabric construction • Structural parameters of knitted fabric against UVR transmission • UV protection provided by stretched or wetted knitted fabrics

5. Background • Aim: Improve UV protection of summer knitwear by modifying the fabric construction • Chemical Approach by using UV absorbers (ZnO,TiO2): • Problem of fiber & dye degradation by photo-catalytic mechanism • Challenges on wash-fastness & adhesion to fabrics • Pollution, water consumption of those chemical treatments • Engineering Approach by modifying fabric construction • Environmental friendly manufacturing process • Especially suitable for knitwear (more elastic and creates more open spaces when stretched) • UV protection enhanced by chemicals is only sufficient when fabric structure is closed enough

6. Previous Findings • Fabric construction with different types of stitches possess distinct UV protection ability • UV protection factor of greige & bleached cotton fabrics with: • Miss stitch >Knit stitch >Tuck stitch • Double Knitted fabrics > Single Knitted fabrics

7. Experimental Details 1. Fabric Specimens Production: Single Knit Structures Notation:

8. Experimental Details 2. Coloration with Reactive Dyes: • Reactive dyes with bi-functional group for better color fastness • Temperature rise process 25-60℃ • L.R. = 50:1 • Four shades: • Red: Levafix Red CA (MFT-TEP) • Yellow: Remazol Yellow 3RS (MCT-VS) • Blue: Levafix Navy Blue E-BNA (FCP-VS) • Black: Remazol Black A (VS-DCT) • Three level of depths: 0.1%, 1%, 3%

9. Measurements of UPF • Ultraviolet Protection Factor (UPF) indicates how much UVR is blocked by a textile materials (e.g. UPF 20 allows 1/20th of UVR passing through fabric) • Measured by Cary 300 Conc UV-Vis spectrophotometer with a schott UG 11 filter in a dry, flat and tensionless state (un-stretched) • Australian/New Zealand Standard (AS/NZS 4399:1996) • In Vitro Method: Transmittance (T%)of UV spectrum (290-400 nm) through fabric and calculating the ratio of erthemally weighted solar UVR irradiance measured by a detector with and without fabric sample in place • UV protective clothing should have a minimum UPF 15 • ↑ UPF ≈ ↓ Transmittance

10. Measurements of Color Yield (K/S sum) • Measured by a Macbeth Color Eye 7000A spectrophotometer • Acquired at CIE standard observer 10° viewing angle • Under CIE standard illuminant D65 (daylight illumination) • Specimens were folded into layers to ensure opacity but without stretching • K/S Sum value is calculated by summation of each K/S value within the visible spectrum (400-700 nm) with 10 nm intervals: • ↑ K/S ≈ ↑ Concentration of colorant in the medium

11. Results & Discussions • No major difference in color yield (K/S sum) whereas distinct difference in UPF among various knit structures in red & yellow colored fabrics • Knit & Miss structures have higher UPF than All Knit and Knit & Tuck structures • ↑ UPF ~ ↑ dye concentration (color depth) • Although darker colored fabric provides superior UV protection, thermal comfort is a concern especially for summer wear. • Darker shaded clothes absorb more infra-red radiation causing wearer feels hot K/S Sum K/S Sum

12. Results & Discussions • No major difference in color yield (K/S sum) whereas distinct difference in UPF among various knit structures in red & yellow colored fabrics • Color is not a reliable indicator for UV protective performance of fabrics • UV protection depends on dye’s absorption characteristics in UV region which further controlled by their specific structural attributes rather than the chemical class of the dye (Srinivasan et al., 2000) K/S Sum K/S Sum

13. Conclusion • For colored cotton fabrics with the 4 single knit structures: • Knit structures have significant influence in UPF but not for Color yield (K/S sum) • Knit & Miss structure provides better UV protection in all the 4 colors than the All Knit and Knit & Tuck structures • ↑ UPF ~ ↑ dye concentration (color depth) • Darker shaded clothing may not be suitable for summer wear ∵higher absorption of IR radiation, feel hotter • To achieve thermo-physiological comfort, fabrics with Knit & Miss structure are recommended for lighter shaded clothing

14. Future Works • With various knit constructions: • Influence of stretching and wetting on UV protection of knitwear with various knit constructions • Effect of fiber type • Yarn structures e.g. bulkiness & hairiness • Impact of laundering and abrasion affect UPF of various knit structures

15. References Acknowledgement 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. • Ultraviolet radiation and human health (2009). Retrieved May 10, 2011 from http://www.who.int/mediacentre/factsheets/fs305/en/index.html • Skin Cancer Facts (2010). Retrieved June 20, 2011 from http://www.cancer.org/Cancer/CancerCauses/SunandUVExposure/skin-cancer-facts • J. Fan, & L. Hunter, Engineering Apparel Fabrics and Garment, Cambridge: Woodhead: Textile Institute; Roca Raton, Fla.: CRC, 309-338, (2009). • The American Society for Testing and Materials, ASTM D1776-04, Standard Practice for Conditioning and Testing Textiles. • Australian/New Zealand Standard, AS/NZS 4399:1996, Sun protection clothing – Evaluation and classification. • M. Srinivasan and B.M. Gatewood, Textile Chemist and Colorist & American Dyestuff Reporter, 32(4), 36-43, (2000). • P.D. Dubrovski and D.Golob, Textile Research Journal, 79(4), 351-359, (2009).

16. Thank you!