**5.2.3 Clearing phase**

Because disperse dyes have such limited solubility in water, some particulate disperse dye may still be occluded on fibre surfaces after the dyeing phase is complete (Aspland, 1997). If not removed, this surface contamination can undermine the brightness of shade as well as the wash, sublimation and crock fastness results. Commonly, the dyed polyester is cleared of surface-deposited dye as well as auxiliaries (e.g. carriers, surfactants) by means of treatment with detergent or reductive or oxidative treatments, in order to secure optimum fastness of the dyeing and also to improve the brightness of shade (Burkinshaw, 1995).

The usual treatment carried out, especially in heavy depth, is reduction- clearing, where the dyed fibre is treated in a strong reducing bath, usually made up of sodium dithionite and caustic soda. A treatment for 20 minutes at approximately 70-80C, is often sufficient to clear the fibre surface, but the ease of removal varies from chromophore to chromophore and dye to dye. This treatment acts to destroy loose azo disperse dye through chemical reduction of the azo link (Fig. 17). Anthraquinone disperse dyes are not fully destroyed by such a treatment but a degree of removal of surface dye is achieved through temporary solubilisation of the disperse dye to the alkali-leuco form. (Aspland, 1997).

Fig. 17. Chemical reaction during reduction clearing

Research indicates that the polyester dyer will typically reduction-clear in the range of 30- 50% of production shades and sometimes an even higher proportion in blend dyeing. Minimizing the need for reduction-clearing can lead to substantial productivity improvements and water and chemical savings as well as a reduction on the effluent load and should be a key objective in implementation of a rapid dyeing approach for polyester.

Dyeing with Disperse Dyes 217

Biedermann, W. (1972). Classification of Types of Precipitation Occurring in Disperse

Bird, C. L. Partovi, H. K & Tabbron, G. (1959). The Dyeing of Cellulose Acetate with

Broadbent, A. D. (2001). *Basic Principles of Textile Coloration*, SDC, ISBN 0-901956-76-7,

Brunnschweiler, D & Hearle, W. S. (Ed.) (1993). *Tommorow's Ideas and Profits;* 

Burkinshaw, S. M. (1995). *Chemical Principles of Synthetic Fibre Dyeing*, Blackie Academic &

Chao, Y. C. & Chen, S. S. (1994). Dyes for polyester microfibres, *Dyes Pigm.*, Vol. 24, No. 3,

Cegarra, J. & Puente, P. (1967). Considerations on the Kinetics of the Dyeing Process of

Choi, J-H., Hong, S-H. & Towns, A. D. (1999). Azobenzene disperse dyes-past development

Choi, J-H., Hong, S-H. Lee E-J. & Towns, A. D. (2000). Structure-wet fastness relationships of

Dawson, J. F. (1983). The Structure and Properties of Disperse Dyes in Polyester Coloration, *J. Soc. Dyers Colour.*, Vol. 99, No. 7-8, (July 1983), pp. 183–191, ISSN 0037-9859 Dawson, J. F. (1984). Fifty Years of Disperse Dyes *Rev. Prog. Coloration*, Vol. 14, No. 1, (June

Dawson, J. F. (1991). Azobenzene disperse dyes-past development and future prospects,

Dawson, T. L. & Todd, J. C. (1979). Dye Diffusion-The Key to Efficient Coloration, *J. Soc. Dyers Colour.*, Vol. 95, No. 12, (December 1979), pp. 417–426, ISSN 0037-9859 Denton, M. J. & Daniels, P. N (Ed.) (2002), *Textile Terms and Definitions*, The Textile Institute,

Derbyshire, A. N., Mills, W. P. & Shore, J. (1972). The Role of Auxiliary Products in the

Fothergill, F. (1944). A Nomogram to help in the Dyeing of Fine and Coarse Filament

Fourness, R. K. (1979). The Contribution of Disperse Dyes to Progress and Development in

Freeman, H. & Sokolowska, J. (1999). Developments in Dyestuff Chemistry, *Rev. Prog.* 

*Coloration*, Vol. 10, No. 1, (June 1979), pp. 61–68, ISSN 0557-9325

*Coloration*, Vol. 29, No. 1, (June 1999), pp. 8–22, ISSN 0557-9325

Vol. 75, No.12, (December 1959), pp. 600–604, ISSN 0037-9859

Professional, ISBN 0-7514-0043-2, Glasgow, UK

(September 1994), pp. 205–222, ISSN 0143-7208

0037-9859

Bradford, UK

343–350, ISSN 0040-5175

2000), pp. 273–278, ISSN 1472-3581

1984), pp. 90–97, ISSN 0557-9325

ISBN 1-870372-44-1, Manchester, UK

(April 1944), pp. 93–95, ISSN 0037-9859

(November 1972), pp. 389–394, ISSN 0037-9859

ISSN 1472-3581

9859

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Dyeing, *J. Soc. Dyers Colour.*, Vol. 88, No. 9, (September 1972), pp. 329–332, ISSN

Disperse Dyes VIII– Determination of Fibre Saturation Values, *J. Soc. Dyers Colour.*,

*Polyester 50 years of Achievement*, Textile Institute, ISBN 1-870812-49-2, Manchester,

Polyester Fibers with Dispersed Dyes, *Textile Res. J.*, Vol. 37, No. 5, (May 1967), pp.

and future prospects , *Color. Technol.*, Vol. 115, Issue 1, (January 1999), pp. 32–37,

some blue disperse dyes for polyester, *Color. Technol.*, Vol. 116, Issue 9, (September

*J. Soc. Dyers Colour.*, Vol. 107, No. 11, (November 1991), pp. 395–400, ISSN 0037-

High–temperature Dyeing of Polyester, *J. Soc. Dyers Colour.*, Vol. 88, No. 11,

Rayons and Spun Rayons to the Same Shade*, J. Soc. Dyers Colour.*, Vol. 60, No.4,

Textile Coloration: An Historical Review containing Personal Experience, *Rev. Prog.* 

In the cases of pale and medium-depth dyeings or for those dyes which cannot withstand reduction-clearing, the dye fibre can be given an alkaline scour (Waring & Hallas, 1990); residues of anthraquinone dyes which may remain after reduction-clearing, may be removed using an oxidative treatment (Nunn, 1979).

#### **5.3 Thermosol process**

Thermosol dyeing process is important continuous process for dyeing polyester and polyester/cellulose fibre mixture with disperse dyes, which is used mainly for wovens and knitted materials (H. K. Rouette, 2000).

A dispersion of the disperse dye is padded onto the polyester fabric. The material is then dried using a hot flue air dryer or by infrared radiation, the latter usually giving much less migration of the dye. Final drying of the padded material takes place using heated cylinders and the dry fabric is then heated in air, or by contact with a hot metal surface, to a temperature in the range of 190-220C for 1-2min. In hot air, as the fabric approaches the maximum temperature, the disperse dyes begin to sublime and the polyester fibres absorb their vapours (A. D. Broadbent, 2001).

Dyes of lower molar mass tend to sublime more readily, but they also suffer from low fastness and poor resistance to heat treatments. Dyes of higher molar mass have better fastness properties but are more difficult to apply. After thermofixation, scouring or even a reduction-clearing treatment is necessary to remove any dye remaining on the fibre surfaces (R. M Christie et al, 2000).

PET seatbelt webbing is typically dyed with disperse dyes using thermosol dyeing processes in which the webbing is dipped continuously into a dye solution and passed through a hot chamber (ca. 220C) for approximately 2–3 min. The dyestuffs can penetrate the molecular chains of the fibres during their exposure to the hot chamber. This method has some advantages that could avoid a batchwise process (a conventional dyeing method), which is regarded as time-consuming and tedious, and would speed up the dyeing process.

### **6. References**


In the cases of pale and medium-depth dyeings or for those dyes which cannot withstand reduction-clearing, the dye fibre can be given an alkaline scour (Waring & Hallas, 1990); residues of anthraquinone dyes which may remain after reduction-clearing, may be

Thermosol dyeing process is important continuous process for dyeing polyester and polyester/cellulose fibre mixture with disperse dyes, which is used mainly for wovens and

A dispersion of the disperse dye is padded onto the polyester fabric. The material is then dried using a hot flue air dryer or by infrared radiation, the latter usually giving much less migration of the dye. Final drying of the padded material takes place using heated cylinders and the dry fabric is then heated in air, or by contact with a hot metal surface, to a temperature in the range of 190-220C for 1-2min. In hot air, as the fabric approaches the maximum temperature, the disperse dyes begin to sublime and the polyester fibres absorb

Dyes of lower molar mass tend to sublime more readily, but they also suffer from low fastness and poor resistance to heat treatments. Dyes of higher molar mass have better fastness properties but are more difficult to apply. After thermofixation, scouring or even a reduction-clearing treatment is necessary to remove any dye remaining on the fibre surfaces

PET seatbelt webbing is typically dyed with disperse dyes using thermosol dyeing processes in which the webbing is dipped continuously into a dye solution and passed through a hot chamber (ca. 220C) for approximately 2–3 min. The dyestuffs can penetrate the molecular chains of the fibres during their exposure to the hot chamber. This method has some advantages that could avoid a batchwise process (a conventional dyeing method), which is

Aspland, J. R. (1992). A Series on Dyeing, Chapter 8: Disperse Dyes and Their Application to

Aspland, J. R. (1993). A Series on Dyeing, Chapter 9: The Structure and Properties of

Aspland, J. R. (1997). *Textile Dyeing and Coloration*, AATCC, ISBN 0-9613350-1-7, NC,

Baldwinson, T. M. (1989). Post-stentered wash fastness of disperse dyes on polyester-the

Biedermann, W. (1971). Effect of Crystal Modification on Dyeing Behaviour of

Polyester, *Text. Chem. Col.*, Vol. 24, No. 12, (December 1992), pp. 18–23, ISSN 0040-

Disperse Dyes And Related Topics, *Text. Chem. Col.*, Vol. 25, No. 1, (January 1993),

significance of various test conditions, *J. Soc. Dyers Colour.*, Vol. 105, No. 7-8,

Disperse Dyes, *J. Soc. Dyers Colour.*, Vol. 87, No. 4, (April 1971), pp. 105–111, ISSN

regarded as time-consuming and tedious, and would speed up the dyeing process.

removed using an oxidative treatment (Nunn, 1979).

**5.3 Thermosol process** 

knitted materials (H. K. Rouette, 2000).

their vapours (A. D. Broadbent, 2001).

(R. M Christie et al, 2000).

**6. References** 

490X

USA

0037-9859

pp. 21–25, ISSN 0040-490X

(August 1989), pp. 269–276, ISSN 0037-9859


Dyeing with Disperse Dyes 219

Koh, J. Oh, M-J., Kim, H. & Kim, S. D. (2006). Alkaline Dissolution Monitoring of Radial-

Leadbetter, P. W. & Leaver, A. T. (1989). Disperse Dyes - the Challenge of the 1990s:

Lewin, M. & Pearce, E. M. (Ed.) (1985). *Handbook of Fiber Science and Technology, Volume IV*,

Lewis, D. M. (1999). Coloration in the Next Century, *Rev. Prog. Coloration*, Vol. 29, No. 1,

McCarthy, B. J. & Burdett, B. C. (1998). Eco-labelling and Textile Eco-labelling, *Rev. Prog.* 

Mehta, H. P. & Peters, A. T. (1981). Substituent Effects on the Colour, Dyeing and Fastness

Murray, A. & Mortimer, K. (1971). Carrier Dyeing, *Rev. Prog. Coloration*, Vol. 2, No. 1, (May

Nunn, D. M. (Ed.) (1979). *The Dyeing of Synthetic Polymers and Acetate*, SDC, ISBN 0-901956-

Oakes, J. (2001). Photofading of Textile Dyes, *Rev. Prog. Coloration*, Vol. 31, No. 1, (June

Patterson, D. & Sheldon, R. P. (1959). The Dyeing of Polyester Fibres with Disperse Dyes.

Peters, A. T. & Chao, Y. C. (1990). 1,4-Bis(arylamino)-5-nitro-(and 5-amino-)-8-

Peters, A. T. & Cheung, S. K. (1985). Dyestuffs for synthetic polymer fibres: 4-*N*-

Perspiration Fastness Subcommittee. (1952). Investigations into Fastness to Perspiration,

Peters, A. T. (1985). Dyestuffs for Synthetic Polymer Fibres: 4-*N*-morpholinoazobenzenes,

Schroeder, H. E & Boyd, S. N. (1957). Dyes for the Hydrophobic Fibers1, *Textile Res. J.*, Vol.

Trotman, E. R. (1984), *Dyeing and Chemical Technology of Textile Fibres*, John Wiley & Son,

Waring, D. R. & Hallas, G. (Ed.) (1990). *The Chemistry and Application of Dyes*, Plenum Press, ,

*Pigm.*, Vol. 13, No. 2, (June 1990), pp. 123–133, ISSN 0143-7208

27, No. 4, (April 1957), pp. 275–285, ISSN 0040-5175

Mechanism and Kinetics of the Process for Purified Dyes, *Trans. Faraday Soc.*, Vol.

hydroxyanthraquinones: bluish-green dyes for synthetic polymer fibres, *Dyes* 

morpholinoazobenzenes, J. Chem. Tech. biotechnol., Vol. 35, Issue 7, (October

*J. Soc. Dyers Colour.*, Vol. 68, No. 10, (October 1952), pp. 392–394, ISSN 0037-

*J. Chem. Tech. Biotechnol.,* Vol. 35, No. 7, (July 1985), pp. 335–340, ISSN 0268-

Properties of 4-N-β-cyanoethyl-N-β-hydroxyethylaminoazobenzenes part I— Monosubstituted Derivatives, *Dyes Pigm.*, Vol.2, No. 4, (October 1981), pp. 259–269,

*Sci.,* 99, Issue 1, (January 2006), pp. 279-285, ISSN 0021-8995

Marcel Dekker Inc, ISBN 0-824773-35-7, New York, USA

*Coloration*, Vol. 28, No. 1, (June 1998), pp. 61–70, ISSN 0557-9325

Moncriff, R. W. (1970). *Man-made Fibres,* Heywood, ISBN 0-592063-32-1, London, UK

1989), pp. 33–39, ISSN 0557-9325

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55 (1959), pp. 1254-1264, ISSN 0014-7672

1985), pp. 335–340, ISSN 1097-4660

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ISBN 0-3064-3278-1, New York, USA

ISSN 0143-7208

36-8, Bradford

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2575

(June 1999), pp. 23–28, ISSN 0557-9325

type Polyester Microfiber Fabrics by a Cationic Dye-Staining Method *J. Appl. Polym.* 

(Meeting Demands for Increasingly Higher Levels of Wash Fastness in the Exhaust Dyeing of Polyester/cellulosic Blends), *Rev. Prog. Coloration*, Vol. 19, No. 1, (June


Giles, C. H. & McKay, R. B. (1963). The Lightfastness of Dyes : A Review, *Textile Res. J.*, Vol.

Gordon, PF & Gregory, P. (1983). *Organic Chemistry in Colour*, Springer-Verlag, ISBN 0-

Green, A. G & Saunders K. H. (1923). The Ionamines: A New Class of Dyestuffs for

Green, A. G. (1924). The Progress of Research in the Jonamine Dyestuffs, *J. Soc. Dyers Colour.*,

Griffiths, J. (Ed.) (1984). *Developments in the Chemistry and Technology of Organic Dyes*,

Hallas, G. (1979). The Effects of Terminal Groups in 4–Aminoazobenzene and Disperse Dyes

Heimanns, S. (1981). Carrier Dyeing, *Rev. Prog. Coloration*, Vol. 11, No. 1, (June 1981), pp. 1–

Heir, S. W., Cornbleet, T. & Bergheim, O. (1946). The Amino Acids of Human Sweat, *J. Biol. Chem.*, Vol. 166, No. 1, (November 1946), pp. 327–333, ISSN 0021-9258 Hoffman, K., McDowell, W. & Weingarten, R. (1968). The Behaviour of Mixtures of

Ingamells, W. (1993). *Colour for Textiles: A User's Handbook*, SDC, ISBN 0-901956-56-2,

Johnson, A. (1989). *The theory of coloration of textiles*, SDC, ISBN 0-901-95648-1, Bradford,

Kassim, S. A. & Peters, A. T. (1973). New Intermediates and Dyes for Synthetic-polymer

Kenneth, J. & Skelly, J. K. (1973). Dyeing of Texturised Polyester Yarn, *J. Soc. Dyers Colour.*,

Kim, I. S., Cho, H. M., Koh, J. & Kim, J. P. (2003). Low-Temperature Carrier Dyeing of

Koh, J. & Greaves, A. J. (2001). Synthesis and Application of an Alkali-clearable Azo

Koh, J. S. & Kim, J. P. (1998a). Sythesis of Phthalimide Based Alkali-clearable Azo Disperse

Koh, J. S. & Kim, J. P. (1998b). Application of Phthalimide Based Alkali-clearable Azo

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(December 2003), pp. 3896–3904, ISSN 0021-8995

3, (September 1998), pp. 265–272, ISSN 0143-7208

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Blackwell Scientific Publications, ISBN 0-632013-04-4, Oxford, UK

Acetate Silk, *J. Soc. Dyers Colour.*, Vol. 39, No. 1, (January 1923), pp 10–16, ISSN

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Disperse Dye Containing a Flurosulfonyl Group and Analysis of its Alkalihydrolysis Kinetics, *Dyes Pigm.*, Vol. 50, No. 2, (August 2001), pp. 117–126, ISSN

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387117-48-2 , New York, USA

0037-9859

ISSN 0037-9859

8, ISSN 0557-9325

0037-9859

0037-9859

0143-7208

UK.

Bradford, UK


**11** 

*India* 

**Pre-treatment of Textiles Prior to Dyeing** 

Cotton is the leading fibre in Textile Industry. Cotton is still the "King" of fibers because most of the world's apparel is made of Cotton. Apart from its fairly good strength, it is considered to provide comfort due to good moisture absorption and wicking properties1. It is estimated that approx. 20 million tons of Cotton is processed worldwide yearly. Unlike man made cellulosic fibers such as Rayon and Lyocell, Cotton must be properly prepared

Amount of water consumed depends to a large extent (refer Table A3), on machine design and complexity of process (refer Table B, C3). Different machines have their own

**1. Introduction** 

Singeing

 Bleaching Neutralization Peroxide removal Bio-polishing Mercerizing

Optical Brightening

 Good desizing effect Removal of seed husks

 High color yield Levelness of the effects

**1.2 Objectives of pre-treatment<sup>2</sup>**

 Lowest possible fiber damage High degree of Whiteness

Good Physical/Technological ratings

for Dyeing, printing and finishing.

**1.1 Typical pre-treatment of cotton involves<sup>2</sup>**

 Desizing (Conventional and Enzyme Processes ) Scouring (Conventional and Enzyme Processes )

Removal of foreign substances from the fibers

High and even Hydrophilicity / Rewettability

**2. Water consumption in textile industry** 

Edward Menezes and Mrinal Choudhari

*Rossari Biotech Ltd., Mumbai,* 

