Indian Journal of Fibre & Textile Research Vol. 24, March 1999,-pp. 64-69

Green technology in textile processing: Part IV-Eco-friendly dyeing of polyester/cotton fabric

H T Deo', A I Wasif, B K Desai & Arindam Chakraborty

Division of Technology of Fibres and Textile Processing,

Department of Chemical Technology, University ofMumbai,

Matunga, Mumbai 400 019, India

Received 31 March 1998; accepted 3 June 1998

New eco-friendly dyeing processes are described for dyeing of polyester/cotton blend fabrics with disperselreactive and di sperse/vat dyes. By process modifications (Eco-Dyeing I and Eco-Dyeing II) and by substituting the non-ecofriendly chemicals with the eco-friendly ones, a significant reduction in pollution load in terms of Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand'(COD) has been achieved. The reductions achieved in BOD and COD respecti vely are 10.47% and 14.38% for dyeing with disperse/reactive dyes and 7.56% and 12.82% for dyeing with disperse/vat dyes. A substantial saving in water consumption has also been achieved in both the methods of dyeing. Eco-Dyeing II , in particular, results in 85% savi ng in water consumption.

Keywords : Disperse dye, Dyeing, Eco-dyeing, Polyester/cotton fabric, Reactive dye, Vat dye, Water recycl in g

I Introduction In recent years, the production capacity of polyes­

ter has increased tremendously in India. Due to the existing tropical conditions, a large proportion of the polyester produced is blended with cotton, viscose and . polynosic fibres . The popularity of polyes­ter/cotton blend is due to its reasonable price, excel­lent combination of aesthetic properties and superior easy care performance I .

In general , the polyester/cotton b~ends are dyed with two classes of dyes by batchwise or continuous methods2

. In India, thtse ble~ds are dyed by the batchwise methods. The most common process is the two-bath dyeing process, wher:ein polyester compo­nent is dyed with disperse dye foilowed by the dyeing of cotton component with· reactive, vat or sulphur dye. Although the two-bath dyeing involves addi­tional labour and is hme consllming, it often produces shades ' of good fastness. For dyeing polyester/cotton blends, disperse/reactive combination is, at times, preferred to disperse/vat combination, because it is comparatively cheap~r. and i's known · for its brilliant shades with good 'fastness properties).

• The author,hoschanged hi s name from H T Lokhande to H T Deo. To whom all the correspondence should be addressed.

Kenyon4 reported that polyester/cotton blends can be dyed by reverse dyeing technique with vinyl sul­phone colours. leI reported a process for batch col­ouration of polyester/cotton blends, wherein alkali stable disperse dyes and high-exhaust reactive dyes (Procion HE) are used. The high stability of HE reac­tive dyes up to 1100e allows the application of both disperse and reactive dyes in a single bath at boil.

Hildebrand and Fiegel5 reported a pH sliding method (a one-bath process) in which the pH of the dyebath containing disperse and reactive dyes is al-10wed to change slowly from alkali:1e to acidic. The reactive dyes are fixed first in the alkaline medium, followed by disperse dyes in acidic medium. Marschner and Hildebrand6 developed AT process (acid fixation) for continuous dyeing of polyes­ter/cellulosic blend fabrics, wherein Levafix EA and Levafix PA dyes react with cellulose in the presence of dicyandiamide without alkali . Saus et aC reported a novel dyeing process using supercritical carbon di­oxide medium that completely avoids water pollution. Vlyssides and Israilides8 characterized the effluent generated during the dyeing of polyester/cellulose blend fabrics .

In the present work, an attempt has been made to dye the polyester/cotton blend fabric with safe dyes,

DEO e( al.: GREEN TECHNOLOGY IN TEXTILE PROCESSING: PART IV 65

eco-friendly auxiliaries and chemicals, and to reduce effluent volume and waste concentration in effluents. Attempts have also been made to achieve savings in water consumption, reuse the low load effluent after suitable treatment and to increase productivity.

2 Materials and Methods 2.1 Materials

Polyester/cotton (70:30) blend fabric having the following specifications was used: warp count, 2/40s; weft count, 20s; pickslin, 62; and endslin,52.

Serene Red RGLS ( c.1. Disperse Red 202), Navi­non Red 6B-90 (C.1. Vat Red 13) and Procion Bril­liant Red H-8B (C.1. Reactive Red 31) were used.

S~dium hydrosulphite (GR grade), common salt, sodium hydroxide, sodium carbpnate, acetic acid, formic acid, calcium chloride, magnesium sulphate, ferric chloride, mercuric sulphate, silver sulphate, potassium dichromate and ferrous sulphate, all of AnaiaR grade, were used as such.

Product CD and Ultra NC ( both from C.D. Corpo­ration, Mumbai) and Sando fix WEI (Clariant India Ltd, Mumbai ) were used.

2.2 Methods 2.2.1 Dyeing

The polyester/cotton fabric was desized, scoured, bleached and mercerized by the conventional meth­ods. The fabric was then dyed with disperse/reactive and di sperse/vat dyes by the conventional method as well as Eco-Dyeing I and Eco-Dyeing II processes.

2.2.1.1 Conventional Dyeing

The two-bath HTHP method was used for dyeing polyester/cotton blend fabric. The cotton component was dyed with reactive and vat dyes using the stan­dard ·methods of dyeing.

2.2.1.2 Eco-Dyeing I

In thi~ process, the polyester component of poly­ester/cotton fabric (5 g ) was dyed first with a dis­perse dye in 1 % shade in a laboratory HTHP beaker dyeing machine and then the cotton component was dyed with a reactive or vat dye in 1 % shade in the same respective bath. The material-to-liquor ratio was kept at I :40. The following sequence was used for the dyeing :

Disperse Dyeing

The dyebath was set at 60°C with a disperse dye and dispersing agent Product CD (lg/l). The pH was

adjusted to 5 with formic acid. The sample was then put into the dyebath and temperature was raised to 130°C in 60 min. Dyeing was carried out at this tem­perature for 60 min. The dyebath was then cooled to 85°C and pH was brought to neutral by adding small quantity of soda ash.

Reactive Dyeing

In the above bath, pre-dissolved salt (20 gil) was added and dyeing was continued for 20 min. Further, 25 gil of pre-dissolved salt was added and dyeing was continued for 25 min. Pre-dissolved sodium carbon­ate (7.5 gil) was added into the bath and dyeing was carried out for 10 min. Remainder sodium carbonate (7.5 gil) was then added and dyeing was continued for 45 min, maintaining the temperature at 85°C. The bath was drained and the sample was rinsed with cold water followed by soaping with 2 gil non-ionic deter­gent Ultra NC at boil for 15 min. Again after draining the bath, the sample was given hot wash followed by a cold wash. The dye fixing treatment was given in the same bath at room temperature (30°C) with dye fixing agent Sandofix WEI (2 gil) after adjusting the pH to 9 with a little quantity of soda ash. The dyebath was drained. Finally, the sample was rinsed with cold water.

Vat Dyeing

In the same bath used for disperse dyeing, the blank vat (5 gi l caustic soda and 5 gil sodium hydro­sulphite) was added followed by the addition of vat­ted dyestuff. Dyeing was continued for 75 min while allowing the bath temperature to drop to 60°C. The bath was then drained and the fabric sample was squeezed and rinsed. Oxidation was carried out with 3mlll hydrogen peroxide (130 vol ) at 60°C for 30 min. The soaping was carried out in the same bath with 2 gi l soap and 2 gil soda ash at boil for 15 min. Finally, the sample was given a hot rinse followed by a cold rinse.

2.2.1.3 Eco-Dyeing II

In the Eco-Dyeing II , the procedure adopted was similar to the one followed in the conventional dye­ing. However, instead of using fresh water, the total wash liquors generated in dyeing of polyester with disperse dye and of cotton with reactive or vat dye were reused after giving the following treatment. The wash liquors generated in polyester dyeing and cotton dyeing were mixed and the pH was brought to 8.5

66 INDIAN 1. FIBRE TEXT. RES., MARCH 1999

with,hydrochloric acid or lime. The solution was then treated with ferrous sulphate (300 mg/l), stirred and kept stagnant for 3 h. The sludge formed was allowed to settle down and the clear liquor was passed through an activated carbon column. This colourless liquor was reused in Eco-Dyeing II.

2.2.2 Tests

Total solids, suspended solids, total dissolved sol­ids, BOD. COD, pH, KlS values, colour difference (by CCM), and colour fastness to washing and day­light were determined as reported earlier.

2.2.3 Assessment of Fastness to Rubbing

Two pieces of fabric (14 cm x 5 cm) drawn from the dyed sample, one having the le~gth direction par­allel to warp yams and th~ other parallel to weft, were used for dry rubbing. Similarly, two more fabric pieces were drawn for wet rubbing. Both the tests were carried out on a crockmeter (World Traders & Co, Mumbai) according to IS: 766(1956) method lO

•

2.2.3.1 Dry Rubbing

One test piece was fixed to the crockmeter. An­other piece of the dry undyed bleached cotton cloth was fixed in a place over the end of the finger of the crockmeter and then rubbed to and fro on the dry test piece 10 times in lOs with a downward force of 900 g on the finger.

2.2.3.2 Wet Rubbing

The procedure was similar to that used in dry rub­bing except that a wet undyed bleached cotton cloth was taken in the place of dry cloth. Degree of staining of the piece of undyed cloth was evaluated with the help of Geometric Grey Scale (Staining) and ratings

were assigned.

3 Results and Discussion Waste water generated in dyeing of polyes­

ter/cotton fabric with disperse/reactive and dis­perse/vat dye combinations by conventional, Eco­Dyeing I and Eco-Dyeing II methods was analyzed for pH, total solids, total dissolved solids, suspended solids, BOD and COD. The results are shown in Ta­ble 1.

The effluent generated in dyeing of polyes­ter/cotton fabric with disperse/reactive dye combina­tion by the conventional method shows alkaline pH and high total dissolved solids, which may be due to the usage of J.arge quantity of salt and · various other chemicals. Since the values of BOD and COD are higher in conventional dyeing, certain modifications become essential to reduce the pollution load. In Eco­Dyeing I, which is a single bath modified dyeing pro­cess, the high BOD generating acetic acid, which is normally used in the conventional dyeing, has been substituted with a low BOD generating formic acid. Besides various steps, such as rinsing after disperse dyeing and reduction clearing followed by two rinses, have been avoided in Eco-Dyeing I. Therefore, Eco­Dyeing I effluent shows lower values of total solids, BOD and COD as compared to that shown by the conventional method . The reduction in pollution load in terms of BOD and COD in case of Eco-Dyeing I is 10.47% and 14.38% respectively. In Eco-Dyeing II, the total effluent generated in the conventional method has been put to reuse after giving suitable treatment. The Eco-Dyeing II effluent shows higher values of total dissolved solids, which indicate that dissolved solids from the conventional dyeing are not

Table I-Analysis of waste water generated during dyeing of polyester/cotton fabric with disperse/reactive and disperse/vat dyes

Dyeing pH Total solids Total dissolved Suspended solids BOD COD process mg/l solids mg/I (5 days at 20°C) mg/I

mg/I mg/I

Dlsperse/Reactive Combination Conyentional 8.0 4794 4353 441 296 751 Eco-Dyeing I 8.4 4398 3986 412 265 643 Eco-Dyeing II 8.0 5802 5326 476 340 885

Disperse! Vat Combination Conventional 9.7 5317 4733 584 357 928 Eco·Dyeing I 10.0 4969 4437 532 330 809 Eco-Dyeing " 9.7 5986 5378 608 379 1023

BOD-Biochemical oxygen dem~d; COD-Chemical oxygen demand

DEO et al. : GREEN TECHNOLOGY IN TEXTILE PROCESSING: PART IV 67

removed during the treatment. Only marginal in­crease in the BOD and COD values of Eco-Dyeing II effluent indicates that substantial amount of dyes and various chemicals are removed from the conventional dyeing effluent by the treatment. Thus, not only the saving in water consumption is achieved but also re­duction in pollutio!1 load of effluent has been ef­fecteli, improving the quality of effluents to be reused in Eco-Dyeing II.

The effluent from the conventional dyeing of poly­ester/cotton fabric with disperse/vat dye combination shows alkaline pH and much higher values of total solids, total dissolved solids, suspend~d solids, BOD and COD. In Eco-Dyeing I, chemical oxidation with non-ecofriendly potassium dichromate and acetic acid has been avoided and instead oxidation with eco­friendly hydrogen peroxide carried out. Besides, a number of steps being followed in conventional dye­ing have been eliminated in Eco-Dyeing I. Thu"s, hot rinse after disperse dyeing, reduction clearing, and hot and cold rinse after reduction clearing have been eliminated. Oxidation and soaping are carried out in the same bath. Therefore, the effluent generated in Eco-Dyeing I shows much lower values of total dis­solved solids, BOD and COD as compared to that shown by the effluent in conventional dyeing with vat

Table 2- KlS values of polyester/cotton fabric dyed with disperse/react ive and disperse/vat dyes

Dyeing process

ConventIOnal Eco-Dyeing I Eco-Dyei ng II

KlS value

DisperselReactive

6.9607 7.2374 6.2058

DisperseN at

5.4032 5.3917 4.9435

dyes. In Eco-Dyeing I, reduction in BOD and COD values is 7.56% and 12.82% respectively. In Eco­Dyeing II, the total effluent of the conventional dye­ing has been reused after giving suitable treatment. Therefore, the effluent of Eco-Dyeing II shows higher values of total dissolved solids. However, BOD and COD values increase only marginally in Eco-Dyeing II effluent.

Table 2 shows the KJS values of polyester/cotton fabric dyed with disperse/reactive and disperse/vat dye combinations. It is observed that the sample dyed by Eco-Dyeing I shows higher KJS value as compared to the conventionally dyed sample in case of dis­perse/reactive dyes. This indicates that the single bath dyeing process as adopted in Eco-Dyeing I achieves higher dye uptake . However, the sample dyed by Eco-Dyeing II shows somewhat lower KJS values than the conventionally dyed sample. The lower dye uptake for the sample dyed by Eco-Dyeing II may be attributed to much higher amount of total dissolved solids present in the recycled water which may be interfering with the dissolution of dyestuffs . In case of dyeing with disperse/vat dyes, it is observed that conventional dyeing and Eco-Dyeing I do not show any significant difference in terms of KJS values. However, the sample dyed by Eco-Dyeing II shows lower KJS value in comparison to those dyed by con­ventional and Eco-Dyeing I methods, indicating low dye uptake in Eco-Dyeing II method.

Table 3 shows that both "dry and wet rubbing fast­ness of samples dyed with disperse/reactive combi­nation by conventional dyeing and Eco-Dyeing I re­main unaltered . However, for Eco~Dyeing II, slight lowering of ratings of dry and wet rubbing fastness is observed for disperse/reactive combination. In case of disperse/vat combination, however, the ratings re-

Table 3-Fastness properties of polyester/cotton fabr ic dyed with di sperse/reactive and disperse/vat dyes

Dyeing process Fastness to Rubbing Washing Light

Dry Wet Co lour change Staining on white

Disperse/Reactive Combination Conventional 4-5 4 4 4 5 Eco-Dyeing I 4-5 4 4 4 5 Eco-Dyeing II 4 3-4 4 3-4 4-5

Disperse/Vat Combination Conventional 5 4-5 4-5 5 6 Eco..oyeing I 5 4 4-5 5 6 Eco-Dyeing " 5 4-5 4-5 5 6

68 INDIAN J. FIBRE TEXT. RES., MARCH 1999

Table 4-Water consumption in dyeing of polyester/cotton fabric with disperse/reactive and disperse/vat dyes

Amount of water, litre Step. Conventional JEco-Dyeing I Eco-Dyeing II

Disperse dyeing Hot rinse after dyeing Reduction clear Rinse Rinse (after acidification) Reactive dyeing Cold rinse after dyeing Soaping Hot wash after soaping Cold wash Rinsing after dye fixing Total water consumption Total savings per batch of 100 kg fabric Saving in monetary terms

Disperse dyeing Hot rinse after dyeing Reduction clear. Hot rinse Cold rinse Vat dyeing Rinse Oxidation Rinse Soaping Hot rinse Cold rinse Total water consumption Total savings per batch of 100 kg fabric Saving in monetary terms

600 600 400 400 400 150 400 400 400 400 Nil

4150

600 600 400 400 400 150 400 400 400 400 400 400

4950

Disperse/Reactive Combination. 600 600" Nil 600" Nil 400· Nil 400" Nil 400" 150 150" 600 400" 600 400· 600 400" 600 400 600 Nil 3750 400 400 3750b

9.63% 82.41%

DisperseNat Combination 600 600· Nil 600· Nil 400· Nil 400· Nil 400· 150 1.50· 600 400· 600 400· Nil 400· Nil 400" 600 400· 600 400

3150 400 1800 4550b

36.36% 85.04%

• Recycled water, b For two batches (one each by conventional dyeing and Eco-Dyeing II)

main, unchanged in both Eco-Dyeing I and II, except a slight lowering in Eco-Dyeing I for wet rubbing fastness (4-5 to 4). Similarly, the wash fastness and light fastness ratings for conventionally dyed and Eco-Dyeing I dyed samples are identical. These re­sults indicate that the fastness properties are not ad­versely affected in Eco-Dyeing I, in spite that it is a one-bath dye'jng process.

Table 4 shows the water consumption in dyeing of polyester/cotton fabric with disperse/reactive and dis­perse/vat dye combinations. It is observed that in case of disperse/reactive dye combination, Eco-Dyeing I and Eco-Dyeing II result in savings of 400 and 3750 litres water respectively per batch of 100 kg fabric. In monetary terms, the savings obtained per batch in Eco-Dyeing I and Eco-Dyeing II are 9.63% and

82.41 % respectively. The dyeing of polyester/cotton fabric with disperse/vat dye combination by Eco­Dyeing I and II results in savin~s of 1800 and 4550 litres water respectively per batch of 100 kg fabric. In monetary terms, the savings obtained per batch in Eco-Dyeing I and Eco-Dyeing II are 36.36% and 85 .04% respectively.

References I Chavan R B & Jain A K, Dyeing of polyester and its blends,

edite'(j by M L Gulrajani (lIT, New Delhi), 1987,205. 2 Mehra R H, Jhangiani S B, Tolia A H & Mehra A R, in

Blended textiles, edited by M L Gulrajani [The Textile Asso­ciation (India)], 1981, 277.

3 Basu A K, Deb T K, Gandhi R B & Shroff J J, in Blended textiles, edited by M L Gulrajani [The Textile Association (India)], 1981 , 282.

4 Kenyon G H, Am Dyest Rep, 68(3) (1979) 19.

DEO £'1 a/. . GREEN TECHNOLOGY IN TEXTILE PROCESSING: PART IV 69

5 Hildebrand D & Fiegel J, Bayer Farbel/ Review, (34) (1983) 3 1; World Texl Abslr, 17 (1985) 1828, 174.

(j Marschner W & Hildebrand D, in Blel/ded lextiles. edited by M L Gulrajani [The Textile Association (India»), 1981 ,269.

7 Saus W. Knittel D & Schollmeyer E, Text Res J, 63(3) (199.1) 135 .

8 Vlyssides A G & Israilides C J , Fresenius Environ Bull, 6 (11112) (lCl 97) 705; (,helll Abstr, 127 (1997) 282930.

9 Deo H T & Wasif A I, Indian J Fibre Text Res. 24 (1999) 58.

lOIS: 766-1956, lSI handbook of textile testing (Bureau of Indian Standards, New Delhi), 1982.