Indian Journal of Fibre & Textile Research

Vol 29-December 2004-pp 462-469 

Substitute products for urea in application of reactive dyes to cotton fabrics.

Geeta N Shetha & Aparna A Musale 

The Bombay Textile Research Association, L.B.S. Marg, Ghatkopar (W), Mumbai 400 086, India 

Received 28 July 2003; revised received and accepted 7 November 2003 

Caprolactam, PEG 400 and PEG 600 have been identified as partial or complete substitutes of urea in the dyeing and printing of reactive dyes on cotton fabrics. It is observed that the caprolactam in many reactive dyes can replace urea while PEG 400 and PEG 600 are effective for replacement to the extent of about 50% of the optimum concentration of urea required for fixation.

Keywords: Caprolactam, Cotton, Dyeing, Polyethylene glycol, Printing, Urea

IPC Code>: Int. Cl.7: C09B 62/00, D06P 1/38, D06P 3/62

1 Introduction

During dyeing/printing of cellulosic fibres with reactive dyes, the addition of urea to the pad-liquor or print-paste is recommended and it is considered by textile printers that such addition results in brighter and more level prints. Specific action of urea in continuous dyeing or printingwith reactive dyes is highly complex and different opinions have been expressed to explain the results obtained under different conditions of application regarding the role played by urea1-8. Main functions of urea during continuous application of reactive dyes have been found to be the increasing solubility of dye in reaction medium, controlling evaporation of water during drying and swelling of cotton, thereby facilitating the dye-fibre reaction.

However, when dyeings or prints containing urea are washed-off, the urea is decomposed easily producing nitrogenous compounds whichaccelerate the growth of algae, resulting in undesirable stream pollution. Inview of the fact that the environmental regulations regarding stream pollution arebecoming more rigid, different approaches for elimination or replacement ofurea in dyeing and printing have been adopted. Some of them are given below:

• Partial or complete substitution of urea by alternateproducts8-10.
• Controlled mechanical application of moisture beforesample enters in steamer11.
• Controlled drying of urea-free printed fabrics prior tosteaming12.
• Adoption of two-stage printing through flash ageing.

Replacement of sodium alginate by synthetic thickeners.

In the present study, different dye-solublising agents and hydrotropic substances have been examined as chemical substitutes for urea, whereby simple substitution of a more environment-friendly product could be effected.

2 Materials and Methods

2.1 Materials

2.1.1 Fabric

Mills desized, scoured, mercerized and bleached cotton fabric(warp count 30s; weft count 30s; ends/inch 96; and picks/inch 60) was used inthe study. The procedures followed for desizing, scouring, mercerizing andbleaching were as follows:

Desizing

• Amylase enzyme :0.8 g/L
• Calcium chloride:1 g/L
• Sodium chloride :1 g/L
• Duration :4h
• pH :7.0
• Machine :JT-10 (Jig)

Scouring

• Sodium hydroxide:4 % owf
• Wetting agent :0.5%
• Temperature :950C
• Duration :3h
• Machine :JT-10(Jig)

Mercerization

• Scoured fabric was mercerized with 300 g/L caustic soda.

Bleaching

• H2O2:2% owf
• Stabiliser:0.6% owf
• Wetting agent:0.3% owf
• Temperature:950C
• Duration:2h

Fabric was given hot and cold wash and neutralized with 0.5-1g/L acetic acid at every stage of operation.

2.1.2 Dyes

Vinyl sulphone reactive dyes used were

C.I. Reactive Yellow15, C.I. Reactive Yellow 37, C.I. Reactive Orange 107, C.I. Reactive Orange 16, C.I. Reactive Red 35, C.I. Reactive Red 37, C.I. Reactive Violet 5, C.I. Reactive Blue 21, C.I. Reactive Blue 19 and C.I. Reactive Black 5.

2.1.3 Chemicals

Substitute products (laboratory reagent) used werecellosolve, glycerine, sorbitol, polycarboxylic acid, polyethylene glycol (200,400, 600, 4000) and caprolactam.

2.2 Methods

2.2.1 Dyeing

2.2.1.1 Pad-dry-cure Method

Padding liquor consisted of following ingredients:

• Dye:40 g/L
• Urea or substitute product:20-80g/L
• Sodium bicarbonate:36 g/L
• Water:904-844 ml
• Total:1000 g

Fabric was padded on ERNST BENZ AG padding mangle with dyesolution keeping an expression of 80%, dried at 80 oC and cured inWerner Mathis AG Drier Steamer at 140 oC for 90 s.

2.2.1.2 Pad-dry-steam Method

Padding liquor consisted of following ingredients: Dye:40 g/L Urea or substitute product:20-80g/L NaHCO3:18 g/L Water:922-862 ml Total:1000 g Fabric was padded with dye solution keeping an expression of80%, dried at 80oC and steamed in Star Steamer at 100-103oCfor 7 min.

2.2.2 Printing

2.2.2.1 Print-dry-cure method

Print paste consisted of following ingredients:

• Thickening agent Sodium alginate, 8%:450 g/kg
• Dye:40 g/kg
• Urea or substitute product:10-100g/kg
• Resist salt:15g/kg
• NaHCO3:25 g/kg
• Water:460-370 ml
• Total:1000 g

Fabric was printed, dried at 90oC and cured at 140oCfor 90 s.

2.2.2.2 Print-dry-steam Method

Print paste consisted of following ingredients:

• Thickening agent Sodium alginate, 8%:450 g/kg
• Dye:40 g/kg
• Urea or substitute product:10-100g/kg
• Resist salt:15g/kg
• NaHCO3:20 g/kg
• Water:465-375 ml
• Total:1000 g

Fabric was printed, dried at 90oC and steamed at100-103 oC for 10 min. Dyed or printed fabrics were washed with 5g/L non-ionic detergent at 95oC for 30 min to remove unfixed dye.

2.2.3 Colour Strength Measurement

Colour strength (K/S) was calculated fromreflectance measurements carried out on Macbeth Color Eye-7000Aspectrophotometer using the following Kubelka-Munk equation:

K/S = [(1 – R)2/2R ]

where R is the reflectance; K,

the absorption coefficient; and S, the scattering coefficient.

3 Results and Discussion

3.1 Substitution in Dyeing

Table 1 - K/S values for vinyl sulphone dyes used in presence of different amounts of urea

It is known that the quantity of urea normally recommendedfor incorporation in pad liquor varies between 50 g/L and 60 g/L depending onthe method of fixation adopted. However, this is not the optimum amount formaximum fixation of reactive dyes, and it varies from dye to dye and type ofreactive system in the dye molecule. Therefore, in the present study, theoptimum concentrations of urea required under given set of conditions have beenobtained for each dye examined using pad-dry-cure and pad-dry-steam techniques.Subsequently, the effect of reducing this quantity progressively and replacingit by alternate substitutes without any adverse effect on the extent offixation has been examined.

Table 1 indicates that in case of pad-dry-cure technique, theextent of fixation increases as the concentration of urea increases from 10 g/Lto 80 g/L. With C. I. Reactive Orange 107 and Red 35, beyond 60 g/L ureaconcentration the fixation remains more or less the same while with C. I.Reactive Yellow 15 and Blue 19, the optimum quantity of urea is 80 g/L. In caseof pad-dry-steam technique, beyond an optimum concentration (20g/L), furtherincrease in concentration to 80 g/L results in a decrease in fixation or theextent of fixation remains the same. Such reduction in fixation is likely to bebecause of rupture of vinyl sulphone dye-fibre bond due to the combinedalkaline action of urea and sodium carbonate from bicarbonate. However, with C.I. Reactive Blue 21, which is a metal-complex vinyl sulphone dye and has lowreactivity to cellulose, the extent of fixation increases when the quantity ofurea is increased from 20g/L to 80 g/L.

To evaluate alternate substitutes for urea in dyeing withvinyl sulphone reactive dyes, the main consideration has been given to theability of substitute product to bring about effective solublisation of dye inthe padding liquor and retention of sufficient quantity of moisture in thefabric during the curing stage where fixation of dyes takes place in case ofpad-dry-cure application. Cellosolve, glycerine, sorbitol and polyacrylic acidwere examined for partial substitution. However, it is observed that none ofthese products individually or in combination has been an effective substitutefor urea, and the extent of fixation in every case is always less as comparedto that obtained at optimum concentration of urea.

After intensive screening of several substitute products,three products have been experimentally identified as partial or completereplacement of urea in continuous methods of dyeing. These are polyethyleneglycols (PEG) 400 and 600 and caprolactam.

Table 2 - K/S values for vinyl sulphone dyes used in presence of different molecular weight PEG

Product	Conc. of product,  g/L	K/S value
		C. I. Reactive Yellow 15	C. I. Reactive Orange 107	C. I. Reactive Red 35	C. I. Reactive Blue 21	C. I. Reactive Black 5
Urea	Nil	7.5	12.6	8.0	10.7	25.6
	60	11.6	16.7	12.4	12.6	27.7
PEG 200	20	9.0	14.1	9.3	11.0	-
	40	9.9	13.0	9.4	10.6	-
	60	9.5	12.3	9.2	11.6	-
	80	8.6	10.9	8.9	11.1	-
PEG 400	20	10.0	16.3	11.3	10.4	27.1
	40	10.5	14.0	11.4	11.7	26.0
	60	10.3	12.9	10.0	11.1	22.4
	80	10.3	12.2	10.7	11.1	23.1
PEG 600	20	9.6	15.9	13.1	9.9	28.4
	40	10.4	14.2	10.6	9.9	24.3
	60	9.8	13.3	10.1	10.3	20.1
	80	9.5	12.2	9.4	10.2	17.8
PEG 4000	20	7.3	12.5	11.1	7.1	-
	40	7.1	11.5	10.4	6.4	-
	60	7.0	9.4	9.2	6.5	-
	80	7.0	9.3	8.0	6.4	-

To find out appropriate molecular weight polyethyleneglycols, the PEG molecular weights ranging form 200 to 4000 have been examinedat different concentrations as substitute for urea (Table 2). It isobserved that the PEG 400 and PEG 600 show comparable fixation for C I.Reactive Orange 107, Red 35 and Black 5, while C. I. Reactive Yellow 15 andBlue 21 show lower colour value as compared to that observed at optimumconcentration of urea in case of dyeing with continuous methods. Caprolactam at60-80 g/L concentration shows fixation, for most of the dyes, equivalent tothat observed at optimum concentration of urea, irrespective of the method ofdyeing. Thus, PEG 400 and PEG 600 can replace urea partially while caprolactamcan replace urea completely in case of continuous methods of dyeing (Tables2-4, Fig.1).

3.2 Substitution in Printing

As mentioned earlier, three substitute products have beenidentified as partial or complete replacement for urea in the dyeing of cottontextiles with reactive dyes using continuous methods of application, viz.pad-dry-cure and pad-dry-steam techniques. It was, therefore, thought desirableto examine the feasibility of urea substitution by these three substituteproducts during printing with reactive dyes, as urea is used asdye-solubilising agent as well as a hydrotope in large quantities during printing.

Table 3 - K/S values for vinyl sulphone dyes used in presence of different molecular weight PEG at optimum concentrations

Pad-dry-steam

Dye	K/S value
	Pad-dry-cure				Pad-dry-steam
	Urea		PEG 400 (20 g/L)	PEG 600 (20 g/L)	Urea			PEG 400 (10 g/L)	PEG 600 (10 g/L)
	Nil	60 g/L			Nil	20 g/L	60 g/L
C. I. Reactive Yellow 15	7.5	11.6	10.0	9.6	14.2	15.8	15.5	12.9	12.6
C. I. Reactive Orange 107	12.6	16.7	16.3	15.9	18.1	20.0	17.3	21.4	17.2
C. I. Reactive Red 35	8.0	12.4	11.3	13.1	16.4	17.1	15.6	17.3	20.2
C. I. Reactive Blue 21	10.7	12.6	10.4	9.9	18.8	16.9	21.6	19.9	17.7
C. I. Reactive Black 5	25.6	27.7	27.1	28.4	29.0	29.3	30.3	30.1	30.1

>

Table 4 -K/S values of printed samples produced with vinyl sulphone dyes in presence of different amounts of urea

Print-dry-steam

Dye	K/S value
	Print-dry-cure						Print-dry-steam
	Nila	10a	20a	50a	70a	100a	Nila	10a	30a	50a	70a	100a
C. I. Reactive Yellow 15	2.2	2.2	2.1	3.3	7.2	14.8	25.1	24.5	25.0	25.0	26.7	25.8
C. I. Reactive Orange 107	-	4.2	6.4	12.3	21.2	21.4	26.3	25.7	25.2	25.3	25.5	24.7
C. I. Reactive Red 37	3.8	4.1	6.1	9.9	16.9	23.3	27.3	27.4	27.1	27.0	26.6	26.6
C. I. Reactive Blue 28	2.7	3.5	5.5	9.9	13.6	14.8	-	-	-	-	-	-
C. I. Reactive Blue 19	-	-	-	-	-	-	15.6	14.9	15.7	16.7	19.3	21.4
C. I. Reactive Blue 21	2.6	3.5	4.1	6.4	13.1	14.7	22.9	22.7	23.0	23.3	24.5	25.6
C. I. Reactive Black 5	-	11	15.2	21.6	25.1	25.2	-	-	-	-	-	-
aUrea concentration in g/L

In the first instance, the optimum concentrations of urearequired for effective fixation of different reactive dyes by print-dry-cureand print-dry-steam techniques of application were determined. Once thisquantity was determined, the effect of substitute products could be determinedwithout any adverse effect on the extent of fixation.

Table 4 shows that in case of print-dry-cure technique, as the concentration of urea is increased from 70g/kg to 100 g/kg, the colour value increases for C. I. Reactive Yellow 15, Red37, Blue 28 and Blue 21 while with C. I. Reactive Orange 107 and Black 5, theincrease in concentration of urea has practically no effect on the extent of fixation.

In case of print-dry-steam technique, with C. I. ReactiveBlue 19 and Blue 21, the extent of fixation increases progressively as theconcentration of urea in the print paste is increased from 50 g/kg to 100 g/kgprint paste while with C. I. Reactive Yellow 15, Orange 107 and Red 37, thefixation remains more or less the same with or without urea. With later threedyes, the marginal decrease is observed in presence of urea (Table 4). Thisdecrease is likely to be due to the increase in alkali content in the printpaste as a result of combination of higher quantities of urea and bicarbonate,which, in turn, may result in rupture of vinyl sulphone dye-fibre bond.

For studying feasibility of partialor complete substitution of urea, PEG 400, PEG 600 and caprolactam have beenexamined both for print-dry-cure and print-dry-steam methods. As thesesubstitute products are acidic (pH 5.0-6.0) in nature, the compatibility withsodium alginate thickener was examined by viscosity measurement in Brookfieldviscometer. The changes in viscosity of print paste in the absence and presenceof dye show comparable results among the entire three substitute productsindividually and in combination with urea in comparison to the results obtainedat optimum concentration of urea in the print paste. Fig. 1 - Reflectance (K/S)values of dyeings produced with vinyl sulphone dyes applied by continuous methods in presence of optimum concentrations of caprolactam Fig. 2 - Reflectance (K/S) values of printed samples produced with vinyl sulphonedyes applied by print-dry-cure method in presence of different products atoptimum concentrations

Subsequently, the printing wascarried out in presence of different substitute products and urea. The resultsindicate that in case of print-dry-cure method of fixation, it is not possibleto substitute urea completely by any of the three substitute products whencompared to the results obtained at optimum concentration of urea (100 g/kg)(Fig. 2). However, the dye fixation is always higher than that obtained in the absence of urea in print paste.

In case of combination of urea (50% of optimumconcentration) with the increase in concentration of each of the threesubstitute products, the extent of fixation increases. The optimumconcentration obtained for both PEG 400 and PEG 600 is 30g/kg, while forcaprolactam it is 50g/kg when used along with 50g urea/ kg print paste forcomparable fixation (Fig.3). However, PEG 400 gives more or less comparablefixation for C. I. Reactive Yellow 15, Orange 107 and Red 37 while lower colourvalue is observed for C. I. Reactive Blue 19 and Blue 21, as compared to thatobserved at optimum concentration of urea. PEG 600 gives comparable fixationfor C. I. Reactive Orange 107 and Red 37 and lower fixation for C. I. ReactiveYellow 15, Blue 19 and Blue 21 as compared to that obtained at optimum concentration of urea.

Fig. 3 - Reflectance (K/S) values of printed samples produced with vinyl sulphonedyes applied by print-dry-cure method in presence of different products atoptimum concentrations and reduced quantity of urea

Fig. 4 - Reflectance (K/S) values of printed samples produced with vinyl sulphonedyes applied by print-dry-steam method in presence of different products atoptimum concentrations

Fig. 5 - Reflectance (K/S) values of printed samples produced with vinyl sulphonedyes applied by print-dry-steam method in presence of different products atoptimum concentrations and reduced quantity of urea

Table 5 - Biodegradability of urea and different substitute products

Caprolactam shows comparable fixation to that of urea for all dyes studied except C. I. Reactive Blue 21.

In case of print-dry-steam method offixation, 50g/kg of caprolactam completely replacesurea for equivalent fixation obtained at optimum concentration of urea(70g/kg) for all the dyes studied (Fig. 4). PEG 400 or PEG 600 alone at 20g/kgin print paste gives colour value comparable to that observed using 70g/kg ofurea (Fig. 4), except for C. I. Reactive Blue 19 and Blue 21. However, at 50%of optimum concentration of urea (35 g/kg print paste) and 20 g/kg PEG 400 orPEG 600, the fixation is comparable to that observed using 70g/kg urea alone(Fig. 5). In case of C. I. Reactive Blue 19, the presence of PEG 400 or PEG 600gives marginally lower colour value as compared to that observed at optimumconcentration of urea.

Biodegrability iscalculated in terms of BOD/COD ratio. Results indicate that biodegrad­abilityof the substitute products is greater than that of urea (Table 5).

4 Conclusion

It appears possible to partially substitute urea by two specific types of polyethylene glycols andin some cases even complete substitution can be effected by caprolactam withoutmuch sacrifice in colour value of dyeings/prints. Products are biodegradable.

Acknowledgement

The authors arethankful to the Ministry of Textiles, Government of India, for sponsoring thisresearch project. They are also thankful to Dr. A N Desai, Director, BTRA, forthe support and to Prof. E H Daruwalla for valuable discussion during thecourse of work.

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