Coloration of textiles

1. NATURAL DYESOpportunities for a greener textile and coloration industryDr. Richard S. BlackburnCentre for Technical TextilesUniversity of Leedsr.s.blackburn@leeds.ac.uk

2. Coloration of textiles • Textiles essential to everyday life • Dyeing characterised by high environmental pollution and high health risk to personnel handling harmful substances (dyes, auxiliaries, etc.)* • Synthetic colorants can be harmful and cause allergies in humans† • 1856 William Perkin accidentally discovered Mauveine • Research into natural dyes over last 150 years very limited • Consumer demand for 'natural' products incorporating natural ingredients • Move to find renewable resources (synthetic colorants from finite resources, e.g. petroleum) • Search for new sources of natural colorants has intensified • Interest in natural dyes has recently increased * Blackburn, RS, Burkinshaw, SM. Green Chem. 2002, 4 (1), 47. † Lea, AGH. In: Atsuchi, K (Ed.), HPLC in Food Analysis, Academic Press, London.

3. Natural colorants • Some ‘experts’ highlight various problems(land for growth, poor technical performance) • Others concentrate on advantages of technologies based on sustainable resources* • Textile, coloration and agricultural industries in UK all require rejuvenation • Use of natural colorants offers a potential to link all three areas • Development of new alternative crops is a principal objective of the DEFRA Science and Innovation Strategy • Synergy needed between different sectors by pooling different knowledge bases • Provision of high quality raw materials linked to novel dyeing methods applying natural dyes * Hill, DJ. Rev. Prog. Color. 1997, 27, 18.; Ali, SI. J. Soc. Dyers. Color. 1993, 109, 13.

4. Current limitations of natural dyes • Traditionally yield and concentration lower than synthetic dyes • Large quantities of raw material to obtain the same depth of colour • Limited success in coloration of synthetic fibres (polyester has a 45% share of the global textile market) • Nearly all natural dyes need application with a mordant (salts of Cr, Sn, Zn, Cu, Al, Fe) to secure sufficient wash and light fastness and to give good build-up • Effluent contains heavy metals far in excess of allowable limits • Argued that employing mordants of Al and Fe negative environmental impact is lower • Extremely desirable to develop new methods of fixation using non-metal mordants • Some research ongoing within EC (AIR2.CT94.0981) to determine how natural dyes can be produced and used in sustainable and efficient processes† • Modern cultivation methods of producing: • Isatis tinctoria (woad), Reseda luteola (weld), Solidago virgauria (golden rod), Rubus tinctorum (madder) † Hancock, M. Potential for colourants from plant sources in England and Wales. 1997, ST0106.

5. Examples of natural dyes • Madder produces red anthraquinone dye in its roots, most important being alizarin (1) • Weld produces yellow flavanoid colorants from foliage and flowers, most important being luteolin (2) 2 1

6. Extraction • Dyes have been extracted from plant material by a number of methods, not all entirely ‘green’ • Desirable to extract using superheated water • ‘Clean’ solvent with minimal environmental impact • Recently reported* that polyphenol dyes have been successfully and rapidly extracted from elderberry, raspberry and blueberry using water at 120°C • Superheated water under pressure between 125 and 175°C has been shown to rapidly extract the oxygenated compounds† • Extraction by superheated water could be a viable process for production of high quality natural colorants * Lauro G J; Francis F J. Natural food colorants: science and technology, Proceedings of a symposium. Institute of Food Technologists,1999, 336. † Delgado-Vargas F; Jimenez A R; Parades-Lopez O. Crit. Rev. Food Sci. Nutrit. 2000, 40, 193-195.

7. Objectives ofGreen Chemistry Group (UoL)and opportunities for research • Identify the key variables affecting the production of sustainable, consistent plant based dye compounds • Develop environmentally friendly extraction and concentration processes • Develop a range of natural and environmentally safe textile dyes • Develop coloration processes using natural dyes to obtain high colour depth and high fastness dyeings on natural fibres • Employment of non-metal mordants to enhance these parameters • Develop coloration processes using natural dyes to obtain high colour depth and high fastness dyeings on synthetic fibres • Application of natural dyes using scCO2 • Chemically modify natural dyes to enhance fastness and to secure additional colour gamut (range of shades) on a variety of substrates • Develop pilot-scale dyeing processes

8. Objectives ofGreen Chemistry Group (UoL)and opportunities for research • Important non-textile natural coloration research opportunities: • Packaging • Plastics • Cosmetics • Personal care • Food } improve biodegradability of system? } direct human contact/consumption

9. Toxicology • Unmodified natural dyes may have a significantly lower environmental impact (broken down through biological processes) • Should not assume that ‘natural’ means safe • Toxicology of successful natural dyes needs to be researched extensively • Will not require new testing, as all potential natural compounds will have extensive testing already carried out • Any chemical modification of the dyes may require new toxicology testing

10. LCA • Life Cycle Assessment of the whole textile dyeing process will be essential to demonstrating the sustainability of this proposed system • University of Leeds researchers experienced in this type of assessment • LCA will study environmental aspects and potential impacts throughout the product’s life (i.e. ‘cradle-to-grave’) • from plant material growing • land use • acquisition through processing • application • end use • disposal

11. Expertise @ UoL • Richard Blackburn • Colour chemistry, coloration processes, dye-fibre interactions, fastness testing • Chris Rayner • ‘Green’ chemical modification, applications in scCO2 • Tony Clifford • ‘Green’ extraction processes, superheated water