1. New green chemical techniques in textile coloration processes
Dr. Richard S. Blackburn
Senior Lecturer and Head of Green Chemistry Group
Centre for Technical Textiles
UNIVERSITY OF LEEDS, LS2 9JT, UK

2. Where can Green Chemistry have an impact in Coloration?
Dye chemistry
Alternative synthesis, sustainable source, natural platform chemicals
Dyes in effluent
Reduction (efficiencies of sorption) and cleaner treatment technologies
Auxiliary chemicals
Reduction in use and emission of harmful auxiliaries (e.g. salt, reducing agents, carriers)
Application processes
Reduction in energy, water usage, time
Coloration of ‘greener’ fibres
PLA, PHAs, lyocell, etc.
© University of Leeds 2006

3. Sustainable platform chemicals
Natural dyes derived from plant material represent a more sustainable source of colorants
Natural dyes colour natural fibres (cotton, wool, silk) to a greater or lesser extent
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
Natural dyes have found limited success in coloration of synthetic fibres
PET has a 45% share of the global textile market
Madder plant (Rubia tinctorum L.) is an important dye plant
produces the dye alizarin (1,2-dihydroxyanthraquinone)
also contains rubiadin (1,3-dihydroxy-2-methylanthraquinone) and purpurin (1,2,4-trihydroxyanthraquinone)
© University of Leeds 2006

4. Sustainable platform chemicals
Derivatisation of alizarin to produce more hydrophobic molecule
higher affinity for hydrophobic polyesters
Successful synthesis of 1-hydroxy-2-ethylanthraquinone (1H2EA)
93% yield
confirmed by FT-IR and NMR
OH at 1-position not derivatised due to intramolecular hydrogen bond formation and lower intrinsic reactivity
© University of Leeds 2006

5. Sustainable platform chemicals
Problem with application of alizarin is pH sensitivity
1H2EA displays no such sensitivity due to derivatisation of 2-OH
Table: The effect of pH on solubility and colour of alizarin and 1H2EA pH
Alizarin
1H2EA 4
v. sparingly soluble
no colour
insoluble 7
sparingly soluble
orange/yellow colour 10
soluble
purple colour
© University of Leeds 2006

6. Sustainable platform chemicals
Dyes applied with dispersing agent to PET and PLA
Colour strength (K/S) achieved with 1H2EA higher than alizarin
Dyeings unlevel, poor quality with alizarin
Dyeings level, bright, good quality with 1H2EA
Alizarin gives higher K/S on PET w.r.t. PLA, but opposite observed for 1H2EA
increased interactions with PLA via alkyl chain addition
Table: Colour strength (K/S) values of dyed samples
Conditions of application
Alizarin
1H2EA
PET
PLA
1% omf at 90 °C
1.5
4.3
1% omf at 100 °C
3.1
2.1
5.1
1% omf at 130 °C
6.5
8.7
4% omf at 115 °C
2.2
10.6
4% omf at 130 °C
19.2
20.9
© University of Leeds 2006

8. Sustainable platform chemicals
Wash fastness comparable and excellent on all dyeings
Light fastness considerably higher for 1H2EA compared to alizarin
2-OH susceptible to photo-oxidation, as it cannot form an intra-molecular H-bond
In 1H2EA 2-OH derivatised, so not as susceptible to photo-oxidation
Table: Light fastness of dyed samples (1-8 scale)
Conditions of application
Alizarin
1H2EA
PET
PLA
1% omf at 90 °C 3 5
1% omf at 100 °C 6
5/6
1% omf at 130 °C 4
4% omf at 115 °C
3/4
4% omf at 130 °C
© University of Leeds 2006

9. Green Chemistry Sulphur Dyeing
Economical, good colour strength, good fastness dyeings on cellulosics
Significant share of the colorants market
annual consumption of ca. 70,000 tons
C. I. Sulphur Black 1 alone represents a substantial portion (20-25%) of dyestuff market for cotton
highest consumption of any single textile dye in the world
Complex mixtures of reproducible, but uncertain, compositions
Contain within their ring structure thiazole, thiazone, or thianthrene as chromophores
All sulphur dye molecules contain disulfide linkages
© University of Leeds 2006

10. Mechanism of sulphur dyeing
Initially dye is in insoluble oxidised (pigment) form
Addition of reducing agent cleaves a proportion of the disulfide linkages to form the partially soluble ‘leuco’ sulphur form
Further addition of reducing agent and increase in redox potential causes reduction of the remaining disulfide linkages and quinoneimine groups
After exhaustion of the dye onto fibre, the reduced, adsorbed dye is reformed in situ within the fibre by air or chemical oxidation
© University of Leeds 2006

11. Reducing agents in sulphur dyeing
Sulphur dyes themselves have a relatively low detrimental environmental impact
free from heavy metals and AOX
Significant environmental problem with the dyeing process
employ sulfides as reducing agents
90% of all sulphur dyes are reduced using sodium sulfide
Discharge of sulfides only permissible in very small amounts (usually the legal allowance is 2 ppm)
danger to life from liberated hydrogen sulfide
corrosion of sewerage systems
damage to treatment works
high pH
aquatic life down stream significantly affected
damage to the DNA of tadpoles
classed as micropollutants
over time the substance can reach high concentrations
© University of Leeds 2006

12. Alternative reducing agents
Thiourea dioxide from both a practical and ecological point of view
dyeings comparable, but environmental effect unclear
significantly more expensive than sodium sulfides
Indirect cathodic reduction processes
successfully reduce sulphur dyes
some reducing agent was required to prevent premature re-oxidation of the dye
dyeing was comparable
electrolysis is an appreciably more expensive technology
Glucose/NaOH
above 90°C has sufficient reducing potential
no current systems in commercial use
dyeings secured had lower colour strength and fastness
no fundamental work on the reducing sugar/NaOH system conducted to understand optimum
© University of Leeds 2006

13. Application of various reducing D-sugars
D-arabinose
D(-)-fructose
D(+)-galactose
α-D-glucose
β-D-lactose
D-maltose
sodium polysulfide
sodium hydrosulfide
Blackburn, R. S.; Harvey, A. Env. Sci. Technol. 2004, 38 (14), 4034.
© University of Leeds 2006

14. D-arabinose
D(-)-fructose
D(+)-galactose
α-D-glucose

15. β-D-lactose
D-maltose

16. Environmental and economical considerations
Relative theoretical COD and price of reducing agents per kg dyed cotton
Reducing agent
g O2 kg-1 dyed cottona
£ kg-1 dyed cottona
sodium sulfide
51.3
1.60
sodium hydrosulfide
71.3
1.18
D-arabinose
66.6
28.06
D(-)-fructose
1.65
D(+)-galactose
4.14
α-D-glucose
0.58
β-D-lactose
70.1
2.08
D-maltose
4.30
a Based on 2.5 g dm-3 reducing agent (typical optimum concentration) at a liquor ratio of 25:1
© University of Leeds 2006

17. Greener reactive dyeing of cellulose
Treatment of cellulose with cationic, nucleophilic polymers to enable reactive dyeing at neutral pH without electrolyte addition
Reactive dyeing problems
High electrolyte concentrations used
High colour concentrations in effluent
High volume of water consumed
© University of Leeds 2006

18. Problems with high electrolyte concentration
High levels of salt (sodium sulfate/chloride) used when dyeing cotton
Particularly reactive dyes
Fibre has negative charge in water
Repels anionic dyes – low adsorption
Electrolyte screens negative charge
Overcomes repulsion between dye anions and negative fibre surface to allow adsorption
Soil too alkaline to support crops
Kills aquatic life
Examples of fresh water courses turned saline downstream from reactive dyeing operations
Difficult to remove from effluent
© University of Leeds 2006

19. Mechanism of reactive dye fixation to cellulose (Nucleophilic substitution)

20. Mechanism of reactive dye fixation to cellulose (Michael Addition)

21. Colour (unfixed dye) in effluent
Reactive dyes poor fixation
10-40% dyestuff hydrolysed
Goes down drain
Aesthetically unpleasant
Blocks sunlight
Algae overpopulate
Reduction in O2 levels in water
Suffocation of flora and fauna in watercourses
Clean effluent
High cost
© University of Leeds 2006

22. High water consumption
High level of water used in reactive dyeing
Incredible volume used in wash-off of hydrolysed dye
Up to 10 separate rinsings
High energy consumption
50% total cost dyeing procedure
© University of Leeds 2006

23. Pre-treatment agents
Copolymer of diallyldimethylammonium chloride and 3-aminoprop-1-ene (PT1)
Copolymer of
4-vinylpyridine quaternised with 1-amino-2-chloroethane
(PT2)
© University of Leeds 2006

24. High substantivity of pre-treatments for cotton
Both pre-treatment polymers are highly substantive to cellulosic fibre
ion-ion interactions between cationic groups in the agent and the anionic carboxylic acid groups in the substrate
low pKa values will be ionised at the pH values of application (pH 6-7)
Other forces of attraction
H-bonding, van der Waals
© University of Leeds 2006

25. Conformational interaction between
PT1
Conformational interaction between
PT1 and cellulose
© University of Leeds 2006

26. PT2
Ion-dipole interactions between cellulose hydroxyl groups and pyridinium residues of PT2
Yoshida H-bonding between cellulose hydroxyl groups and pyridine residues in PT2
© University of Leeds 2006

27. Mechanism of operation (schematic)
© University of Leeds 2006

28. Advantages of pre-treatment system
Polymers cationic
No requirement for salt
Nucleophiles in polymer more reactive than hydroxyl groups in fibre
Neutral pH of application
Hydrolysis minimised
Colour fixation yield maximised
Less colour in effluent
Less wash-off requirement
Significant reduction in operation time
Significant reduction in water consumption
© University of Leeds 2006

29. System comparison Procedure Wash-off stages Time (mins)
Water (ℓ/kg fabric)
NaCl (g/kg fabric)
Na2SO4 (g/kg fabric)
Na2CO3 (g/kg fabric)
Other Chemicals (g/kg fabric)
Remazol RR 6
355
145
1250
500
acetic acid (60), detergent (20)
Procion H-EXL 4
365
105
1625
detergent (20)
Cibacron F 5
295
125
1500
Pre-treatment 1
195 50
pre-treatment (10), detergent (20)

30. Publications
Blackburn, R. S.; Burkinshaw, S. M. Green Chemistry (1), 47.
Blackburn, R. S.; Burkinshaw, S. M. Green Chemistry 2002, 4 (3), 261.
Blackburn, R. S.; Burkinshaw, S. M. Journal of Applied Polymer Science, 2003, 89,
“Dye Hard”, New Scientist, 1st December 2001
“Greener Dyes”, The Alchemist, 6th February 2002
“Problem Fixed”, Chemistry in Britain, April 2002
© University of Leeds 2006

31. DyeCat Ltd. A University of Leeds Spinout Company Dr. Patrick McGowan
Organometallic chemistry
Novel polymerisation catalysts
Organometallic anticancer drugs
Dr. Richard Blackburn
Coloration of natural and synthetic polymers and fibres
Physical organic chemistry of dyeing processes
Green Chemistry in the textile and coloration industries
Prof. Chris Rayner
Organic synthesis (pharmaceuticals and fine chemicals)
Supercritical carbon dioxide
Green Chemistry
©DyeCat 2006
© University of Leeds 2006

32. DyeCat Technology
Patented technology for the preparation of light absorbing polymeric materials (IR, visible, UV).
Variety of approaches; allows flexibility in
Polymer composition
Polymer molecular weights and polydispersities
Coloration strength
Range of light absorbing chromophores
Applicable to natural and synthetic polymers (particularly polyesters such as PLA and PET).
Superior coloration technology
Homogeneous colorant throughout cross section of polymer
Increased wash and light fastness
Greatly improved preparative method
Significant cost reductions on comparable conventional technology
Reduced environmental impact
Applicable to sustainable, biodegradable polymers such as PLA and PHB.
©DyeCat 2006
© University of Leeds 2006

33. Contacts Laura Bond (general inquiries) Dr. Patrick McGowan
Dr. Patrick McGowan
Dr. Richard Blackburn
Prof. Chris Rayner
©DyeCat 2006
© University of Leeds 2006

34. Acknowledgements Colleagues Research Assistants PhD Students
Prof. Chris Rayner
Prof. Tony Clifford
Prof. Stephen Burkinshaw
Prof. Carl Lawrence
Prof. Paul Knox
Dr. Patrick McGowan
Dr. Steve Russell
Dr. Abbas Dehghani
Research Assistants
Dr. Tony Blake
Dr. Nagitha Wijayathunga
Dr. Xiangfeng Zhao
PhD Students
Iram Abdullah
Nabeel Amin
Ioannis Drivas
Parikshit Goswami
Anna Harvey
Andrew Hewitt
Nandan Kumar
Wei Zhang
Industrial Partners
Body Shop International plc (UK)
DyStar (Germany)
Lenzing Fibers Ltd. (Austria)
NatureWorks LLC (USA)
Reilly Industries inc. (USA)
Uniqema (UK)
© University of Leeds 2006