Eco-Friendly Sulfur Dyeing of Cellulosic Woven Fabrics

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Eco-Friendly Sulfur Dyeing ofCellulosic Woven FabricsN. A. Ibrahim a , A. R. El-Gamal b & F. Mahrous ba Textile Research Division , National ResearchCenter , Dokki, Cairo, Egyptb Faculty of Applied Arts , Helwan University , Cairo,EgyptPublished online: 14 Feb 2007.

To cite this article: N. A. Ibrahim , A. R. El-Gamal & F. Mahrous (2005) Eco-Friendly Sulfur Dyeing of Cellulosic Woven Fabrics, Polymer-Plastics Technology andEngineering, 44:6, 1059-1078, DOI: 10.1081/PTE-200065174

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Eco-Friendly Sulfur Dyeing of Cellulosic WovenFabrics

N. A. IbrahimTextile Research Division, National Research Center, Dokki, Cairo, Egypt

A. R. El-Gamal and F. MahrousFaculty of Applied Arts, Helwan University, Cairo, Egypt

Abstract: This work demonstrated that conventional sulfur dyeing, which posesenvironmental problems, can be modified by using safer chemicals. The resultsindicate that: i) using reducing sugars as eco-friendly reductants results in animprovement in the extent of coloration; ii) the extent of improvement is determ-ined by the reductant type; i.e., liquid glucose (LG)> thiourea dioxide (TUD)>glucose (G)> molass (M), dye=reductant ratio, as well as type of woven cellulosicfabric; i.e., viscose> cotton> linen; iii) raising the dyeing temperature to 80�C for45min, increasing NaCl concentration to 30 g=L, and=or minimizing the material-to-liquor ratio to 1=10 brings about an improvement in the extent of coloration;iv) efficiency of dye fixation is determined by the nature of the oxidant andfollows the descending order (NH4)2 S2O8>Na-perborate>H2O2>none; andv) post-softening has positive impacts on the softness degree and washing fast-ness, as well as rubbing fastness properties, especially in the case of using thecationic softener, regardless of the sulfur dye used.

Keywords: Cellulose; Ecology; Reducing sugars; Sulfur dyeing; Woven fabric

1. INTRODUCTION

Sulfur dyes constitute a very important class for dyeing cellulosic fibersand their blends[1]. Sulfur dyes are used widely for production of inexpen-sive medium to heavy depth shades; i.e., black, navy, green, and brown,with acceptable fastness properties[2]. With each of the three commer-cially used subclasses of sulfur dye, namely C. I. Sulfur, C. I. LeucoSulfur, and C. I. Solubilized Sulfur, the cellulosic substrate is dyed usingthe reduced or leuco form, thiolate, which has a certain affinity to the

Address correspondence to N. A. Ibrahim, Textile Research Division, NationalResearch Center, Dokki, Cairo, Egypt. E-mail: [email protected]

Polymer-Plastics Technology and Engineering, 44: 1059–1078, 2005

Copyright Q Taylor & Francis, Inc.

ISSN: 0360-2559 print/1525-6111 online

DOI: 10.1081/PTE-200065174

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fiber[2,3]. After the leuco-dye anions have been absorped onto anddiffused into the fiber, they are commonly oxidized, in situ, leaving inso-luble sulfur dye entrapped in the cellulosic substrate[1–4].

Modern environmental standards and traditional harsh chemicals, aswell as auxiliaries used in sulfur dyeing, are often incompatible and muchmore will have to be done. Environmental issues of concern in textile wetprocessing focus mainly on pollution prevention, materials, and energyconservation, as well as waste minimization[4–9].

Accordingly, the main task of the present work is to modify the sul-fur dyeing process to make it eco-friendly, as well as to upgrade the sulfurdyeing quality.

2. EXPERIMENTAL

2.1. Materials

The experimental cellulosic fabrics used throughout this work arebleached cotton (155 g=m2), bleached linen (200 g=m2), and bleached vis-cose (185 g=m2).

The commercial sulfur dyes used are Hydron1 Blue R Stabilosol(Dystar), Sulfol1 Navy Blue SR 50% (HCH), Diresul1 Blue RDT(liquid- Clariant), and Diresul1 Black RDT (liquid-Clariant).

Reducing agents used throughout this work are glucose monohy-drate, glucose liquid (80%), molass, and thiourea dioxide.

Oxidizing agents used are hydrogen peroxide (35%), sodium per-borate, and ammonium persulphate.

Softening agents used are Knitsoft1 WA-ET (a cationic softenerbased on a combination of modified polysiloxane and fatty acid conden-sation compound, Clariant), and Leomin1 NI-ET (a non-ionic fatty acidcondensation product, Clariant).

Other chemicals, such as sodium hydroxide, sodium carbonate,sodium chloride, acetic acid, and Hostapal1 CV-ET (a non-ionic wettingagent based on alkyl aryl polyglycol ether, Clariant), were of commercialgrade.

2.2. Methods

2.2.1. Dyeing

Dyeing with sulfur dyes by exhaust method was carried out in sealed,stainless steel dye pots at a liquor ratio of 20:1 according to the dyeingprocedure shown in Fig. 1.

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2.2.2. After Treatment

Each of the two softening agents was applied at 3% owf using a 20:1liquor ratio at pH 5 (using acetic acid) and at 50�C for 20min.

2.2.3. Testing

The color strength of the dyed samples was measured at the wavelengthof maximum absorbance using an automatic filter spectrophotometer,and calculated by the Kubelka-Munk equation[10]

K=S ¼ 1�Rð Þ2=2R

where K is the light absorption coefficient, S is the light scattering coef-ficient, and R is the reflectance of the dyed sample. The higher the K=Svalue, the greater the color intensity and, hence, the better the dyeuptake.

Fastness properties to washing, dark as well as light dyed samples,were assessed according to AATCC test methods: 61-1972, 8-1972, and16A-1972, respectively.

Softness ratings were determined on coded samples by a hand panelwith a minimum of five members. Fabrics were rated on a scale of 1–55 ¼ very soft; 1 ¼ harshð Þ[11].

3. RESULTS AND DISCUSSION

With a view toward exploring the feasibility of improving the perform-ance properties of sulfur dyeing, as well as minimizing the environmental

Figure 1. Dyeing procedure with R-reducing step, D-dyeing step, O-oxidizingstep, and �-rinsing step. Dye (4% owf), NaOH (5 g=l), NaCl (45 g=l), dye=reduc-reductant (1:0.5–8), and oxidant (2 g=l).

Eco-Friendly Sulfur Dyeing 1061

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impact arising from the sulfur dyeing of cellulosic fabrics, a wide range ofreducing agents, cellulosic substrates, dyeing conditions, salt concen-tration, liquor ratio, dye concentration and type, oxidizing agents, andsoftening agents have been examined. Results obtained along with theirappropriate discussion follow.

3.1. Type and Dye=Reductant Ratio

Results of the change in the dyeability of the used cellulosic substrates;i.e., cotton, viscose, and linen woven fabrics, with Hydron1 Blue R(4% owf) sulfur dye as a function of the reductant type; i.e., glucosemonohydrate (G), liquid glucose (LG, 80%), thiourea dioxide (TUD),or molass (M), as well as dye=reductant ratio (1:0.5–10) are shown inTable 1. Table 1 reveals that: i) increasing dye=reductant ratio from1=0.5 to 1=1 (in case of using G, LG, or TUD as a reductant) or up to1=6 (in case of using M as a reductant) brings about a sharp increasein K=S values of the obtained sulfur dyeings, regardless of the used cellu-losic substrate; ii) further increase in the dye=reductant ratio does notshow significant improvement in K=S values of the dyed substrates;iii) the improvement in K=S values is a direct consequence of increasingthe extent of dye reduction and solubility, as well as improving its pen-etration and diffusion within the fabric structure, thereby promotingthe dye-fiber interaction and fixation via oxidation to the insoluble formaccording to the following reaction steps[4,12],

Dye�S�S�Dyeþ 2H �!alkali=reduction2Dye� S

�Na

�

Soluble mercaptiales or ðthiolatesÞð1Þ

2Dye� S�Na�

þO �!acid=oxidationDye� S� S�DyeþH2O

insoluble sulfur dye ð2Þ

iv) the extent of dyeing, expressed as a K=S value, is determined by thenature of the reducing agent, and follows the descending orderLG > TUD > G > M, which reflects the differences among these reduc-tants in chemical constitution, reduction potential, and ability to reducethe used sulfur dye[4,12]; and v) the differences in K=S values of theobtained sulfur dyeings upon using different cellulosic substrates; i.e.,cotton, viscose, and linen, would be expected to rely on cellulose content,amorphous to crystalline regions, surface area, etc[13–15].


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Table

1.Effectofreductanttypeanddye=reductantratioonthecolorstrength

ofdyed

cellulosicsubstrates

Linen

Viscose

Cotton

K=S

K=S

K=S

Substrate

Reductant

Reductant

Reductant

Dye=reductantratio

GLG

TUD

MG

LG

TUD

MG

LG

TUD

M

1:0.5

3.13

4.95

4.54

–4.09

7.68

6.94

–3.42

6.43

5.06

–1:1

11.23

12.04

11.86

0.69

19.15

20.92

20.25

1.11

11.83

12.92

12.53

0.96

1:2

11.52

12.46

12.19

1.54

19.32

21.26

20.60

2.65

12.19

13.20

12.88

2.22

1:4

––

–5.04

––

–8.23

––

–6.85

1:6

––

–7.76

––

–13.99

––

–9.71

1:8

––

–8.51

––

–14.46

––

–10.06

Hydron1

BlueR

(4%

owf);NaOH

(5g=L);wettingagent(2g=L);NaCl(45g=L);LR

(20:1).

Reductionat70� C

=15min.;Dyeingat80� C

=45min.

Oxidation:H

2O

2(2g=L;35%);aceticacid(2ml=L);at70� C

=20min.

K=S:colorstrength;G:glucose

powder;LG:liquid

glucose;TUD:thioureadioxide;

M:molass.

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3.2. Dyeing Temperature

Table 2 shows the effect of dyeing temperature on the K=S values of thedyed cellulosic substrates. As is evident, and for given dyeing conditions,the K=S values increase by raising the dyeing temperature to 80�C for45min; whereas further increase, up to 90�C, brings about a slightdecrease in K=S values, regardless of the reductant used and the cellulosicsubstrate.

The enhancement in K=S values by raising the dyeing temperature to80�C could be attributed to the higher extent of swelling of the cellulosestructure, disaggregation, reduction and solubility of dye molecules, aswell as diffusion and penetration within the fabric structure, therebyenabling more dye-fiber interaction and fixation after oxidation.

On the other hand, the decrease in K=S values by raising the dyeingtemperature up to 90�C could be associated with a shortage in dye accom-modation sites and=or immature partial oxidation of the sulfur dye at90�C during the dyeing step; i.e., lower K=S values.

For a given set of sulfur dyeing steps, the changes in K=S values as afunction of type of cellulosic substrates under investigation follows thedescending order viscose > cotton > linen.

3.3. Salt Concentration

The effect of NaCl concentration on the K=S values of the used cellulosicsubstrates in the presence of the aforementioned reducing agents is givenin Table 3. It is clear that for given dyeing conditions within the rangeexamined (0–45 g=L), increasing the salt concentration to 30 g=Limproves the K=S values, regardless of the reductant used and cellulosicsubstrate, which is a direct consequence of equalizing the negative chargeand neutralizing the low pH of the internal cellulosic fiber. This increasesthe substantivity of color bearing anions for the cellulosic fibers; i.e.,there is a higher extent of exhaustion and dye-fiber interaction and fix-ation during the following oxidation step[4,15–16]. Further increase in saltconcentration beyond 30 g=L, has a slight positive effect on the K=Svalues. Nevertheless, the extent of dyeing, as well as K=S values, isdetermined by both the efficiency of the reductant and the nature ofthe cellulosic substrate.

3.4. Dyeing Time

Table 4 shows the effect of dyeing time on the K=S values of the sulfurdyeings. It is clear that within the range examined (15–60min), prolong-ing the dyeing time up to 45min at 80�C enhances the extent of dyeing.This could be interpreted in terms of better absorption and diffusion of


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Table

2.Effectofdyeingtemperature

onthecolorstrength

ofdyed


Linen

Viscose

Cotton

K=S

K=S

K=S

Substrate

Reductant

Reductant

Reductant

DyeingTem

p.(�C)

GLG

TUD

MG

LG

TUD

MG

LG

TUD

M

70

8.19

10.85

10.62

6.62

17.38

18.85

18.13

12.70

10.52

11.60

11.12

8.48

80

11.23

12.04

11.86

7.76

19.15

20.92

20.25

13.99

11.83

12.92

12.53

9.71

90

11.02

11.75

11.52

7.48

18.35

19.98

18.88

13.49

11.55

12.56

12.12

9.53

Hydron1

BlueR

(4%

owf);dye=reductantratio(1:1

incase

ofusingG,LG,orTUD,and1:6

incase

ofusingM);NaOH

(5g=L);NaCL

(45g=L);non-ionic

wettingagent(2g=L);LR

(20:1).

Reductionat70� C

=15min.;Dyeingat70–90� C

=45min.

Oxidation:H

2O


=20min.


powder;LG:liquid


M:molass.

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Table

3.Effectofsaltconcentrationonthecolorstrength

ofdyed


Linen

Viscose

Cotton

K=S

K=S

K=S

Substrate

Reductant

Reductant

Reductant

NaCl(g=L)

GLG

TUD

MG

LG

TUD

MG

LG

TUD

M

08.02

8.45

8.22

4.10

14.90

16.09

15.66

7.26

9.98

10.36

9.48

5.40

15

8.58

9.10

8.90

5.65

17.43

18.66

18.30

10.02

10.60

11.42

11.12

7.18

30

10.96

11.70

11.46

7.40

18.62

19.96

19.50

13.25

11.42

12.25

12.00

9.32

45

11.23

12.04

11.86

7.76

19.15

20.92

20.25

13.99

11.83

12.92

12.53

9.71

Hydron1

BlueR

(4%


incase


incase

ofusingM);NaOH

(5g=L);NaCl

(0–45g=L);non-ionic


(20:1).

Reductionat70� C


=45min.

Oxidation:H

2O

2(2

g=L;35%);aceticacid(2ml=L);at70� C

=20min.


powder;LG:liquid


M:molass.

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Table

4.Effectofdyeingtimeonthecolorstrength

ofdyed


Linen

Viscose

Cotton

K=S

K=S

K=S

Substrate

Reductant

Reductant

Reductant

Dyeing

GLG

TUD

MG

LG

TUD

MG

LG

TUD

M

15

6.70

7.85

7.52

3.14

8.94

10.52

10.18

4.66

7.18

8.38

8.12

3.76

30

8.94

10.32

10.02

7.08

14.44

15.86

15.40

9.73

9.65

11.20

10.85

8.22

45

10.96

11.70

11.46

7.40

18.62

19.96

19.50

13.25

11.42

12.25

12.00

9.32

60

11.20

12.02

11.82

7.92

19.10

20.25

19.84

13.85

11.80

12.50

12.32

9.70

Hydron1

BlueR

(4%


incase


incase

ofusingM);NaOH

(5g=L);NaCl

(30g=L);non-ionic


(20:1).

Reductionat70� C


=45min.

Oxidation:H

2O

2(2


=20min.


powder;LG:liquid


M:molass.

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the sodium salts of leuco-dyes onto and into the cellulose structure,thereby giving rise to a higher extent of in situ oxidation and fixationof the used sulfur dye by the subsequent acid-oxidation step[4,17]. Furtherincrease in dyeing time, beyond 45min, results in dyed fabric sampleswith a slight increase in color strength, regardless of the used reductantand cellulosic substrate.

3.5. Dyebath Liquor Ratio

As far as the changes in the K=S values of the dyed substrates as a func-tion of the liquor to material ratio (LR), Table 5 reveals that decreasingthe LR to 10=1 is accompanied by an improvement in K=S values regard-less of the reductant used and substrate; i.e., the lower the LR the betterthe K=S value, which could be attributed to greater availability of

Dye� S�Na�forms within the cellulose structure which are then oxidized,

in situ, back to the insoluble forms; i.e., higher K=S values.

3.6. Dye Concentration

Table 6 clearly shows that within the range examined and for the givendyeing conditions, increasing Hydron1 Blue R shade to 6% owf bringsabout a significant increase in the K=S values as a direct consequence

of increasing Dye� S�Na�forms in the proximity of the cellulose struc-

ture, thereby giving rise to a higher extent of dye re-oxidation, leavinginsoluble dye molecules entrapped in the cellulosic substrate.

3.7. Nature of Sulfur Dye and Performance Properties

Tables 7 and 8 show the effect of using different sulfur dyes; namely,Hydron1 Blue R (sodium sulfide-free dispersed sulfur dye, Dystar), Sul-phol1 Navy Blue SR (insoluble sulfur dye, HCH), Diresul1 Blue RDT,and Diresul1 Black RDT (pre-reduced liquid sulfur dyestuffs with lowsulfur content, Clariant) along with different reducing agents, G, LG,TUD, and M, on the depth of shade, K=S, of dyed fabric samples (Table7), as well as the fastness properties (especially in case of using LG andTUD reductants, Table 8). For a given set of dyeing conditions, it is clearthat the K=S values, as well as the changes in fastness properties, aredetermined by the nature of the sulfur dye; i.e., chemical nature, extentof reduction and dissolution, extent of penetration and diffusion, sub-stantivity to the cellulosic materials, extent of oxidation, extent of trap-ping and embedding within the cellulose structure, and chromophoricgrouping (hue)[4,17].


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Table

5.Effectofdyebath

liquorratioonthecolorstrength

ofdyed


Linen

Viscose

Cotton

K=S

K=S

K=S

Substrate

Reductant

Reductant

Reductant

LR

GLG

TUD

MG

LG

TUD

MG

LG

TUD

M

10:1

11.38

12.05

11.72

7.72

19.05

20.32

19.80

13.52

11.89

12.60

12.23

9.63

20:1

10.96

11.70

11.46

7.40

18.62

19.96

19.50

13.25

11.42

12.25

12.00

9.32

Hydron1

BlueR

(4%


incase


incase

ofusingM);NaOH

(5g=L);NaCl

(30g=L);non-ionic

wettingagent(2g=L).

Reductionat70� C


=45min.

Oxidation:H

2O


=20min.


powder;LG:liquid


M:molass.

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Table

6.Effectofdyeshadeonthecolorstrength

ofdyed


Linen

Viscose

Cotton

K=S

K=S

K=S

Substrate

Reductant

Reductant

Reductant

Dyeshade(%

owf)

GLG

TUD

MG

LG

TUD

MG

LG

TUD

M

10.75

1.07

0.89

0.55

1.12

1.75

1.42

0.96

0.85

1.22

0.98

0.64

24.20

5.98

5.45

3.18

6.38

9.15

8.42

4.85

4.50

6.45

5.96

3.40

410.96

11.70

11.46

7.40

18.62

19.96

19.50

13.25

11.42

12.25

12.00

9.32

613.30

14.36

13.95

9.12

20.80

22.40

21.92

14.90

14.30

15.32

15.02

11.70

Hydron1BlueR

(1–6%


incase


incase

ofusingM);NaOH

(5g=L);NaCl

(30g=L);non-ionic


(20:1).

Reductionat70� C


=45min.

Oxidation:H

2O

2(2


=20min.


powder;LG:liquid


M:molass.

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Table

7.Effectofusingdifferentsulfurdyes

onthecolorstrength

ofdyed


Linen

Viscose

Cotton

K=S

K=S

K=S

Substrate

Reductant

Reductant

Reductant

Sulphurdye

GLG

TUD

MG

LG

TUD

MG

LG

TUD

M

Hydron1

BlueR

10.96

11.70

11.46

7.40

18.62

19.96

19.50

13.25

11.42

12.25

12.00

9.32

Sulphol1

NavyBlueSR

14.01

14.95

14.70

11.35

19.27

20.70

20.15

13.85

14.65

15.62

15.25

12.02

Diresul1

BlueRDT

17.82

19.02

18.60

13.67

20.80

22.40

21.92

17.60

18.72

19.80

19.39

15.54

Diresul1

Black

RDT

21.70

23.45

22.28

16.75

23.90

25.71

25.08

20.25

22.88

24.60

23.25

19.10

Sulfurdye(4%


incase


incase

ofusingM);NaOH

(5g=L);NaCl(30g=L);

non-ionic


(20:1).

Reductionat70� C


=45min.

Oxidation:H

2O


=20min.


powder;LG:liquid


M:molass.

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On the other hand, the extent of dyeing is determined by the efficiencyof the reductants under investigation, LG > TUD, as well as the nature ofthe cellulosic substrate, viscose > cotton > linen, as shown in Table 8.

Table 8 also shows that the wet rubbing fastness of dyed samples islower than the dry rubbing fastness, regardless of the used dyestuffs,which is probably due to unfixed or over-oxidized dye moleculesentrapped in the cellulose structure and having water solubilizing sulfi-nate and sulfonate groups according to the following equation[4,17,18]

D� S� S�D!½O�D� SO

�2 !½O�

D� SO�3 ð3Þ

3.8. Type of Oxidizing Agent

Table 9 shows the effect of using different oxidizing agents; namely,H2O2, Na-perborate, and (NH4)2S2O8 on the K=S values of the dyed

Table 8. Performance properties of dyed cellulosic substrates

Dye Reductant Substrate K=S

WF RF

A St. D W LF

Hydron1 Blue R LG Linen 11.70 4 4 4–5 3–4 6–7Viscose 19.96 4 4–5 4–5 3–4 6–7Cotton 12.25 4 4–5 4–5 3–4 6–7

TUD Linen 11.46 4 4 4–5 3–4 6–7Viscose 19.50 4 4–5 4–5 3–4 6–7Cotton 12.00 4 4–5 4–5 3–4 6–7

Sulphol1 Navy Blue SR LG Linen 14.95 4 4–5 4–5 3–4 6Viscose 20.70 4 4–5 4–5 3–4 6Cotton 15.62 4 4–5 4–5 3–4 6

TUD Linen 14.70 4 4–5 4–5 3–4 6Viscose 20.15 4 4–5 4–5 3–4 6Cotton 15.25 4 4–5 4–5 3–4 6

Diresul1 Blue RDT LG Linen 19.02 5 5 5 3–4 6–7Viscose 22.40 4–5 4–5 4–5 3–4 6–7Cotton 19.80 4 4–5 4–5 3–4 6–7

LUD Linen 18.60 5 5 4–5 3–4 6–7Viscose 21.92 5 5 5 3–4 6–7Cotton 19.39 4 4–5 4–5 3–4 6–7

Dye (4% owf); dye=reductant ratio (1:1); NaOH (5 g=L); NaCl (30 g=L); non-ionic wetting agent (2 g=L); LR (20:1).Reduction at 70�C=15min.; Dyeing at 80�C=45min.Oxidation: H2O2 (2 g=L, 35%); acetic acid (2ml=L); at 70�C=20min.LG: liquid glucose; TUD: thiourea dioxide; WF: wash fastness; RF: rubbing fast-

ness; LF: light fastness; A: alteration; St.: staining on white cotton; D: dry; W: wet.


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Table

9.Effectofusingdifferentoxidizingagents

onthecolorstrength

ofdyed

viscose

substrate

Hydron1

BlueR

Sulphol1

NavyBlueSR

Diresul1

BlueRDT

Diresul1

Black

RDT

K=S

K=S

K=S

K=S

Dye

Reductant

Reductant

Reductant

Reductant

oxidant

GLG

TUD

MG

LG

TUD

MG

LG

TUD

MG

LG

TUD

M

None

16.05

17.15

16.82

11.78

17.68

18.90

18.35

12.72

17.98

20.34

19.83

16.16

21.36

23.25

22.86

17.92

H2O

218.62

19.96

19.50

13.25

19.27

20.70

20.15

13.85

20.80

22.40

21.92

17.60

23.90

25.71

25.08

20.25

Na-perborate

19.26

20.56

20.22

13.79

20.02

21.15

20.61

14.25

21.22

22.75

22.33

18.05

24.28

26.30

25.50

20.56

(NH

4) 2S2O

819.54

20.90

20.63

14.00

20.94

21.82

21.40

14.70

21.54

23.02

22.65

18.38

24.65

26.60

25.89

20.84

Sulphurdye(4%


incase


incase

ofusingM);NaOH

(5g=L);NaCl

(30g=L);non-ionic


(20:1).

Reductionat70� C


=45min.

Oxidation:(2g=L);aceticacid(2ml=L);at70� C

=20min.


powder;LG:liquid


M:molass.

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Table

10.Perform

ance

properties

ofdyed

viscose

fabrics

before

andafter

soft-finishing

Dye

Reductant

Softener

K=S

SR

WF

RF

ASt.

DW

LF

Hydron1

BlueR

LG

None

20.90

34

3–4

4–5

36–7

Nonionic

21.00

44

4–5

4–5

3–4

6–7

Cationic

21.09

54–5

4–5

4–5

46–7

TUD

None

20.63

2–3

43–4

4–5

36–7

Nonionic

20.72

3–4

44

4–5

3–4

6–7

Cationic

20.80

55

54–5

46–7

Sulphol1

NavyBlueSR

LG

None

21.82

34

3–4

4–5

36

Nonionic

21.93

44

44–5

3–4

6Cationic

22.00

54–5

4–5

4–5

46

TUD

None

21.40

2–3

43–4

4–5

36

Nonionic

21.51

3–4

4–5

44–5

3–4

6Cationic

21.69

54–5

4–5

4–5

3–4

6

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Diresul1

BlueRDT

LG

None

23.02

34

3–4

4–5

3–4

6–7

Nonionic

23.09

44–5

44–5

3–4

6–7

Cationic

23.23

55

4–5

4–5

3–4

6–7

TUD

None

22.65

2–3

43–4

4–5

3–4

6–7

Nonionic

22.72

3–4

4–5

45

3–4

6–7

Cationic

22.86

55

55

46–7

Diresul1

Black

RDT

LG

None

26.60

34

3–4

4–5

37

Nonionic

26.72

44

45

3–4

7Cationic

26.85

55

55

47

TUD

None

25.89

2–3

43–4

4–5

37

Nonionic

25.98

3–4

44

4–5

3–4

7Cationic

26.12

55

54–5

47

Sulfurdye(4%

owf);dye=reductantratio(1:1);NaOH

(5g=L);NaCl(30g=L);non-ionic


(20:1).

Reductionat70� C


=45min.

Oxidation:(N

H4) 2S2O

8(2g=L);aceticacid(2ml=L);at70� C

=20min.

Softening:softener

(3%

owf);LR

(20:1);pH

5;at50� C

=20min.

LG:liquid


K=S:colorstrength;SR:softnessrating;WF:wash

fastness;RF:rubbingfastness;LF:light

fastness.

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fabric samples. It is clear that: i) the improvement in the K=S values fol-lows the descending order (NH4)2S2O8 > Na-perborate > H2O2 > None;ii) the differences in the K=S values obtained upon using the aforemen-tioned oxidizing agents could be discussed in terms of differences inchemical composition, pH of the oxidizing bath, oxidation potential, aswell as extent of over-oxidation[4,17], and iii) the extent of the dyeing ofthe viscose substrate is governed by both the nature of the reductant aswell as the type of sulfur dye.

3.9. Post-Softening

The effect of after treatment of dyed viscose fabric samples with each ofthe two softening agents, Knitsoft1 WA-ET (a cationic softener) andLeomin1 NI-ET (a non-ionic softener) using the exhaustion method(3% owf-LR 20:1- pH5- at 50�C for 20min) on the performance proper-ties of the viscose dyed fabric samples is given in Table 10. It is clear that:i) post-softening of the sulfur dyeings results in an even smoother fabricsurface as well as better softness rating, regardless of the softener used;ii) the softening effect of the used softeners is attributed to their lubri-cation behavior affecting both the surface and the interior of the fibers[19];iii) the improvement in softness degree follows the descending order Knit-soft1 WA > Leomin1 NI > None, and is governed by the nature of thesoftener; i.e., chemical composition, molecular weight, film-formingproperties, functionality, location, and extent of deposition, as well asability to fix or entrap the dye molecules[20]; iv) post-softening has prac-tically no effect on the K=S values of the resultant sulfur dyeings, regard-less of the used dyestuffs; v) post-softening has a positive impact on boththe wash fastness and the wet rubbing fastness properties, especially incase of using the cationic softener, which could be attributed to theformation of a large-molecular-size, dye-cationic softener complex oflow aqueous solubility onto and=or into the fiber, as well as formationof a film at the periphery of the dyed fiber, thereby reducing the diffusionof the dye out of the dyed substrate during washing and wet rubbing and,thus, improving the aforementioned fastness properties[21]; vi) post-softening has practically no effect on the light fastness properties of theresultant dyeings; and vii) both the K=S values and fastness ratings aregoverned by the nature of the sulfur dye.

4. CONCLUSIONS

It has been demonstrated that eco-friendly sulfur dyeings can be obtainedvia replacement of hazardous chemicals, such as Na2S and K2Cr2O7,by using safer chemicals (reducing sugar and per-oxygens, respectively).Results obtained reveal that higher color strength along with better


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softness and fastness ratings of sulfur dyeings are achieved by using LGas a reductant (dye=LG 1=1), NaOH (5 g=L), NaCl (30 g=L), LR 1=10 at70�C=20min in the presence of (NH4)2 S2O8 (2 g=L), as an oxidant, alongwith acetic acid (2ml=L), followed by after-softening using cationicsoftener, Knitsoft1 WA (3% owf).

REFERENCES

1. Burkinshaw, S.M.; Collins, G.W. Aftertreatment to reduce the washdown ofLeuco Sulfur dyes on cotton during repeated washing. JSDC 1998, 114, 165.

2. Burkinshaw, S.M.; Collins, G.W. Aftertreatment to improve the washfastness of sulfur dyeing on cotton. Dyes and Pigments 1995, 29 (4), 323.

3. Bechtold, T.; Burtscher, E.; Turcanu, A. Continuous sulfur dyeing withoutreducing agents: fully reduced black I by cathodic reduction. Text. Chem.Color. 1998, 30 (8), 72.

4. Aspland, R. A series on dyeing: sulfur dyes and their application. Text.Chem. Color. 1992, 24 (3), 21.

5. Sekar, N. Towards safer dyes in textile processing. Colourage 2004, 51, 47.6. Kubanik, R. Reduction in the chemical required for sulfur dyeing. Inter.

Text. Bulletin 1998, 3, 85.7. Chakraborty, J.N. Reduction of effluent load in dyeing of cotton fabric.

Indian Text. J. 1993, February, 66.8. Simpson, J.A.; Binkley, J.; McMahon, P.H. New environmental legislation

affecting textile-industry manufacturing. J. Text. Inst. 2002, 91, 65.9. SEAM Project. Guidance Manual-Cleaner Production for Textiles-Sulphur

Black Dyeing. EEAA=Entec: UK Ltd., January 1999.10. Garland, C.E. In: Colour Technology in Textile Chemistry, Gultekin, G. Ed.,

AATCC, 107, 1983.11. Czech, A.M.; Pavlenyi, J.; Sabia, A.J. Silicone softeners for flurocarbon soil

release treatment. Text. Chem. Color 1997, 29 (9), 26.12. Christie, R.M.; Mather, R.R.; Wardman, R.H. The Chemistry of Colour

Application, Blackwell Science Ltd: USA, p. 90, 2000.13. Ibrahim, N.A.; Abo-Shosha, M.H.; Elnagedy, E.I.; Gaffar, M.A. Eco-

Friendly durable press finishing of cellulose containing fabrics. J. Appl.Polym. Sci. 2002, 84, 2243.

14. Mahrous, F. Improving traditional sulfur dyeing of cellulosic fabrics to beeco-friendly. M.Sc. Thesis, Helwan University Cario, Egypt. 2003, 270.

15. Ibrahim, N.A.; El-Sayed, W.A. Low temperature reactive dyeing of cottonfabric. Am. Dyestuff Rep. 1993, 82 (8), 44.

16. Herlant, M. Low salt dyeing of cellulosics. Am. Dyestuff Rep. 1993, 82 (4),19.

17. Guest, R.A.; Wood, W.E.; Sulfur dyes. Rev. Prog. Coloration 1989, 19, 63.18. Shenai, V.A. Technology of Textile Processing. Chemistry of Dyes and Princi-

ples of Dyeing, Vol. II. Sevak Publications: Mumbari, pp. 432–433, 1993.19. Lautenschlager, H.J.; Bindl, J.; Huhn, K.G. Structure activity relationships

of amino functional siloxanes as components in softening. Text. Chem. Color1995, 27 (3), 27.

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20. Teli, M.D.; Paul, R.; Pareshi, P.D. Softeners in textile industry: Chemistry,classification and application. Colourage 2000, 47, 17.

21. Burkinshaw, S.M.; Collins, G.W. The aftertreatment of sulfur dyes oncotton. Dyes and Pigments 1997, 33 (1), 1.


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Documents

Eco-Friendly Sulfur Dyeing of Cellulosic Woven Fabrics