G. A. BAIG: Studies on with indigo, Tekstil 61 (1-6) 65-73 (2012.) 65

Studies on dyeing wool with indigo

Gulzar A. Baig University College of Engineering Multan, Punjab, Pakistan e-mail: [email protected] Received May 2, 2011 UDK 677.016.4:677.31 Original scientific paper

Wool fabric was dyed with indigo through an exhaust technique at various pH values. The non-ionic form of indigo showed the highest substantivity, while the ionic ones exhibited relatively poor substantivity for wool. The wool fibres were best dyed in the appropriate acidic pH range. The chemistry of the indigo dyebath and wool fibres was taken into account to explain the ef- fects of pH on colour strength. The results suggested that hydrogen bonding and ionic interactions were the main reasons for the exhaustion of indigo on wool fibres. The hydrogen bonding were estabilished between the hy- droxyl groups and amide groups of the dye and the fibres, respectively. The ionic interactions worked in the low pH range between the end-amino and ionized groups of the wool fibres and , respectively. Key words: wool, indigo, dyeing, dyebath analysis, colorimetric properties

1. Introduction % of the world wool production. The with vat and studying the effect other producers are China and New of different variables, mainly pH and Although indigo is now exclusively Zealand with 18 and 11% share, re- temperature. Because of the popular- applied on cotton, historical records spectively [6]. The main applications ity and use, indigo was selected for show that about 4000 years ago it was include the apparels, carpets, felt and dyeing wool. One of our clients in- wool that had first been dyed with insulation. Wool is dyed mainly with tended to produce denim look on indigo and it was about in 1500 A.D, acid dyes; however other dyes such woollen fabrics. Very little data was when cotton was dyed with it [1, 2]. as basic, reactive and vat dyes are available about the effect of pH on Stonewashed woolen fabrics have also used though their percentage been reported in the literature [3]. the dyeability of wool with vat dyes. Wool is a fibre that is obtained from share is very less [7-9]. The applica- It was not known at what pH values, animals in the Caprinae family, main- tion of different classes of colorants could we obtain ring or deep dyeing ly sheep, although hair of other mam- clearly shows the versatile chemical and what would be the optimum dye- mals e.g. goats, llamas and rabbits nature of the fibre. Being Proteinous ing temperature conditions. Polyes- may also be considered as wool [4]. in nature, it contains acidic as well as ter-wool blends are important after Wool has several qualities that distin- basic sites in addition to sulphur-sul- Polyester-cotton ones. Previous work guish it from hair or fur: it is crimped; phur bonds and ionic salt linkages. It showed that good colour yield could it has a different texture or handle; it is very susceptible to hydrolysis; be produced on polyester and is elastic; and it grows in staples [5]. therefore, most of the dyeing of wool [10, 11]. It showed that PET-Wool These properties impart greater bulk is carried out in appropriate acidic blends could be dyed with the same and heat insulation properties for medium to avoid loss in mechanical dye thereby simplifying the process. which it is known. Out of 1.3 million properties. In our case it worked very well be- tons per annum of wool, 60 % goes The present work was undertaken to cause poor-light and sublimation into apparel. Australia is the leading dye wool with Indigo. The goal was fastness of indigo on polyester had producer of wool and accounts for 25 to examine the dyeability of wool helped in achieving very nice faded- 66 G. A. BAIG: Studies on dyeing wool with indigo, Tekstil 61 (1-6) 65-73 (2012.) look effects which could be produced dithionite 10 g/L, Temperature 60 °C, 2.5. SEM analysis either by light or through chemical Time 30 min and LMR 40:1 was Surface morphology of the Wool fi- means. fixed while pH was varied from acid- bers was investigated using Scanning Wool fabric dyed with indigo exhib- ic to alkaline regions. All of the sam- Electron Microscope. Samples were ited excellent shade depths as well as ples having been dyed were subjected sputter-coated with Au in Polaron good fastness properties. It could be to cold water rinsing. The dye was coating unit, model E5100 followed dyed in the acidic as well as basic pH oxidized at ambient conditions with by loading sampler holder in the Hi- regions. However, higher pH values atmospheric oxygen. All of the sam- tachi SEM, model S-3000N. Gun-to- almost destroyed the wool fabric. ples were soaped with Sandopan sample distance was 8-9 mm and Wool, being a polypeptide, contains DTC (soaping agent, Clariant) 5 g/L voltage of 5kV was applied to acce- a large many amide groups in its at 40 °C for 10 min; air-dried and lerate electron toward the samples structure. It also contains free amine then tested for colour values. Fig.1 under high vacuum. Electron beam groups at the end of its polymeric showed the complete dyeing cycle focusing, image magnification and chains, although the number of free and the scheme of the Reduction- brightness/ contrast were adjusted to amine groups is less than the carbox- Oxidation Cycle of Indigo. take the micrographs. SmatSEM sof- ylic groups so that the fibre posses a tware was used to acquire the micro- negative charge unless in the appro- 2.3. pH Measurement graphs. priate acidic pH range. These amide pH values of the fresh as well spent and amine groups provide excellent 3. Results and discussion hydrogen bonding sites for the dye dyebaths were measured at room molecules and are considered to temperature. ΔpH (difference in pH 3.1. Analysis of dyebath pH mainly contribute to the substantivity between any two adjacent pH values) for the dye molecules. were measured and presented along Fig.2 showed pH values of the che- Dyebath pH values at the very start as with the pH values. mical bath solution, in the absence of well as at the end of dyeing were indigo, at the start of simulated dyeing in the presence of wool. A detailed monitored and the results presented. 2.4. Colour measurement Effects of varying pH on the dyebath description of dyebath behaviour is composition, colour strength and on Colour Strength (K/S) by SWL given elsewhere [10]. Fig.3 showed the structure of the fibre were dis- method [13] were measured at a spe- pH at the end of simulated dyeing. cussed. This work finds potential uses cified wavelength (λ) using the fol- The behaviour of wool dyebath at the in the hosiery industry where polyes- lowing Kubelka-Munk equation: end of dyeing is quite different from K/S= [(1.0-R )2]/2.0 R ter/wool blends are dyed with dis- λ λ other fibres [10, 11]. Here pH did not perse/acid dye system. These polyes- Where, K - Coefficient of absorption change that abruptly and this was at- of dye at λ , S - Coefficient of scat- ter/wool blends can be dyed in a sin- max tributed to hydrolysis of the peptide tering at λ R - Reflectance of the gle bath with a single dye and excel- max, λ bonds in the fibre. Hydrolysis led to specimen at λ . lent shade depth can be obtained. max the appearance of new amine end Reflection of the samples was measu- groups which absorbed the acidic 2. Experimental red in the range of 400 – 700 nm at moieties. Alkaline pH had drastic ef- intervals of 20 nm. fects on the strength of the fibre. Wool 2.1. Material and machinery

Mathis Labomat IR dyeing machine 80 oC was used to dye wool samples and the 30 min pH measured before and after dyeing 5 oC /min using Digital pH Meter PH- 210. Reflectance and colour strength were measured on Datacolour 500 o Spectrophotometer. Wool: 100% Wool 2 C /min yarn plain woven scoured fabric. Indi- go dye (85 %), granular form, was obtained from BASF. All other chemi- Indigo dye NaOH cals were of laboratory grade. Na2S2O4 Drain Fabric 3x rinising o 2.2. Dyeing 20 C Samples were dyed with Indigo to 0.1-2 % o.w.f shade depth. Sodium Fig.1 Dyeing process profile G. A. BAIG: Studies on dyeing wool with indigo, Tekstil 61 (1-6) 65-73 (2012.) 67 fibres were almost destroyed and lost O OH H H their integrity. The micrograph sho­ N + - N 2H 2e wed that surface of fibres were peeled off and the cuticles were completely N N H H dissolved away. O HO

Fig.4 showed pH of the dyebath at the - [O] OH start of dyeing process in the absence [O] - O OH of wool. The derivative of this curve H H showed two distinct peaks denoted as N N

“a” and “b”. Peak “a” appeared when - N OH N alkali was increased from 0 to 0.2 g/ - H - H O O L. Sodium dithionite produced acidic Scheme I Reduction-oxidation cycle of indigo. products during decomposition even at ambient conditions (25 °C). These acidic by-products lowered down the Chemical bath pH analysis-Start dyebath pH. When alkali was increa- pH-start D?pH start sed this started neutralizing the acidic b 14 20 products and so pH started increasing 18 12 as could be seen from 0.4 upto 0.8 16 10 14 g/L. Peak “b” was appeared when pH D

12 ?pH a alkali concentration was increased 8 / pH 10 from 0.8 to 1.2 g/L. This peak showed ge 6 8 an that now alkali was in excess and that 6 ch pH the acidic products generated by so- 4 4 pH change / 2 dium dithionite were completely neu- 2 0 tralized. The negative scale showed 0 -2 the equivalent amount of acid (hydro- -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 chloric acid in this case). When acid NaOH (gpl) was increased, pH didn’t change up Fig.2 pH (start) of chemical bath at various alkali concentrations (Na2S2O4 10 g/L, to 0.2 g/L and thereafter there was a 80 °C, 30 minutes, LMR 40:1) sudden drop in pH as shown by peak “a”. Peak “a” showed that there were some species that were absorbing pH end Chemical bath pH analysis-End acid. This could be –NH groups in D?pH end pH change indigo molecules. 14 20 Fig.5 showed the dyebath at the end 18 12 of dyeing process. The same two 16 14 pH

10 H b peaks were there, however, the inten- a D 12 ?p

pH 8

sity of peaks was reduced. Since wool 10 e / contained a lot of amino (-NH ) 8 ng 2 6 ha 6 groups in its polymeric structure, it H c p 4 4 pH change / was suggested that wool picked up 2 2 acid generated by sodium dithionite. 0 Peak “a” was shifted from 0 to 0.2 - 0 -2 0.4 g/L alkali concentration. It is -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 known from chemical kinetics that NaOH (gpl) temperature increases the reaction Fig.3 pH (end) of chemical bath at various alkali concentrations (Na2S2O4 10 g/L, rate. At the dyeing temperature (80 80 °C, 30 minutes, LMR 40:1) °C), sodium dithionite was comple- tely dissociated into products. The consumed by wool and leuco vat acid move further away from each other at highly acidic products consumed molecules as well. the end of dyeing. Peak “a” moved to alkali which lowered down the rise in Fig.6 and 7 showed dyebath pH at the the left which meant that pH was in- pH. In addition to byproducts gene- start and end of dyeing, respectively. creased as could be read from the pH- rated by sodium dithionite, alkali was It was evident that peaks “a” and “b” difference curve. There was a negati- 68 G. A. BAIG: Studies on dyeing wool with indigo, Tekstil 61 (1-6) 65-73 (2012.)

Blank bath pH analysis-Start Where e = (pK1 +pK2 – 2pH) and f = pH-start (pK2 - pH) D?pH start Fig.9 showed the reflection spectra of 14 20 indigo dyed wool fibres in various pH 18 12 regions. The results showed that light 16 b 10 14 reflection was high when pH was less pH D a 12 ?pH than 6 but more than 7. Since alkaline

8 / pH 10

ge pH was deleterious for polypeptides,

6 8 an

ch the pH should have been in the acidic 6 pH 4 4 pH change / side to get maximum colour strength 2 with little damage. The reflection mi- 2 0 nima lie at 660 nm in all the cases. 0 -2 3.2. pH vs. Colorimetric properties -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 Fig.10 showed the colour strength of NaOH (gpl) indigo on wool at different pH values. Fig.4 pH (start) of dyebath at various alkali concentrations in the absence of wool The shade depth decreased steeply to (shade: 1 % owf, Na2S2O4 10 g/L, 80 °C, 30 min. LMR 40:1) the left of pH~5 than on higher pH values. Reduction of sodium dithio- ve dip in the pH-difference curve at ping steeply. As the pH increased, di- nite led to the formation of highly 0.2 g/L alkali concentration which sodium form also started appearing. acidic products which were highly meant that at the start pH was low and At pH ≈ 9 both the curves of the leu- soluble in water. Vat acid itself is a very week acid, pKa value 6, and so at end of dyeing it was increased. co vat acid and mono-phenolate form it is sparingly soluble in aqueous me- This increase in pH was due to proto- crossed each other. Beyond this leuco dium. Because of the presence of hi- nation of wool polymer in this region. vat acid diminished steeply and was On the negative alkali concentrations ghly soluble acidic impurities, the converted in to the mono-sodium solubility of the leuco vat acid was (as acid concentration increases) pH phenolate form. At a pH of 9-10, di- at the end was always higher than at reduced to a large extent. If these aci- sodium form started appearing, al- the start. dic products are not consumed, then though it was in minute amount. It was possible to calculate different according to the Le Chatlier’s princi- Fraction II = 1/ (1+10a+10b) (1) fractions of the leuco vat acid, shown ple the reaction should not proceed Where a = (pH – pK ) and b = (2pH in figure 4 which could be present at 1 further i.e. proper colloidal dispersion a particular pH by using the equations – pK1 – pK2) of leuco vat acid. (1), (2) and (3) [12]. It was evident Fraction III = 1/ (1+10c+10d) (2) It was suggested that below pH 4.0, from Fig.8 that vat acid remained as Where c = (pK1 - pH) and d = the acidity was so high in the dyebath that most of the leuco vat acid preci- the major moiety upto pH ≈ 5.5 after (pH – pK2) which its concentration started drop- Fraction IV = 1/ (1+10e+10f) (3) pitated out and this was supported by the observations that at end of dyeing in this region, a black dispersion was produced so very little dye exhausted pH end Blank bath pH analysis-End D?pH end to the wool samples. Although in the pH change pH range of 3 – 5, leuco vat acid was 14 20 the sole product of reduction reaction, b 18 12 due to its poor solubility most of the 16 14 leuco vat acid precipitated from the 10 pH pH 12 D solution. As pH increased above 5, /? pH 8 10 a ge there was a rapid change in pH. The 6 8 an pH jumped from 3.5 to 5.5 that deri- 6 ch pH 4 4 pH change / ved the solubilisation of the leuco vat 2 acid in the forward direction. At pH 2 0 ≈ 6 leuco vat acid still shared ≈ 97% 0 -2 of the strength in the dyebath solu- -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 tion, Fig.8, so a maximum shade dep- NaOH (gpl) th was produced. As the pH increa- Fig.5 pH (end) of dyebath at various alkali concentrations in the absence of wool sed, the mono-sodium phenolate form (shade: 1 % owf, Na2S2O4 10 g/L, 80 °C, 30 minutes, LMR 40:1) also started appearing in the dyebath G. A. BAIG: Studies on dyeing wool with indigo, Tekstil 61 (1-6) 65-73 (2012.) 69

but unlike polyester (PET), it was Dyebath pH analysis-Start pH-start also absorbed by the wool fibres. A D?pH start 14 20 nearly flat plateau was formed in the 18 pH range of 6 to 8.00. In the whole 12 16 pH region, wool fibres continued to 10 14

pH absorb the dye molecules. Above pH D b 12 ?pH 8.00, wool fibres were de-protonated 8 a / pH 10 ge thereby leaving the mono-sodium 8 an 6 6 ch phenolate form in the solution. Howe- pH 4 4 pH change / ver, the decreasing quantities of leuco 2 2 vat acid continued to tint the fibre. 0 The shade depth increased sharply 0 -2 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 above pH 5, Fig.6, therefore pH NaOH (gpl) should be controlled carefully and never let be dropped below 5.5 othe- Fig.6 pH (start) of dyebath at various alkali concentrations in the presence of wool rwise there would be wastage of co- (shade: 1 % owf, Na2S2O4 10 g/L, 80 °C, 30 minutes, LMR 40:1) lorants. Another point from the graph was very clear that pH control was crucial because if pH were less than

pH-end Dyebath pH analysis-End 6, there would be less shade depth D?pH end being produced while pH higher than pH change 14 20 6 upto 8 did not affect shade depth 18 12 and there was severe damage to the 16 fibres. 10 14 pH pH 12 D 3.3. Effect of reducing agent 8 /? pH 10 b nge

8 a 6 The following Fig.11 showed the ef-

a ch 6 fect of sodium dithionite on color pH 4 4 pH change / yield of indigo on wool fibres. The 2 2 sodium dithionite concentration was 0 0 -2 varied at a constant pH of 6. The re- -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 sults showed that upto a concentra- NaOH (gpl) tion of 6 g/L, the color strength was low; however, as the concentration Fig.7 pH (end) of dyebath at various alkali concentrations in the presence of wool was increased color strength increa- (shade: 1% owf, Na S O 10 g/L, 80 °C, 30 minutes, LMR 40:1) 2 2 4 sed as well. An increase in concentra- tion of sodium dithionite decreased the color strength. The results showed Dyebath compostion vs. pH that there should have been an opti- Fraction II mum concentration of sodium dithio- 1 Fraction III nite. Too little a concentration was 0.9 Fraction IV not sufficient to reduce all the dye 0.8 molecules completely and therefore 0.7 no dye buildup while increase in con-

n 0.6 centration of sodium dithionite above io

act 0.5 a certain concentration again reduced Fr 0.4 the shade buildup which was attribu-

0.3 ted to the dye over-reduction and side

0.2 reactions. 0.1 3.4. Effect of temperature 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 The following Fig.12 showed the ef-

pH fect of dyeing temperature on color yield of indigo on wool fibres. It was Fig.8 Fraction of leuco vat acid as a function of pH observed that the graph was quadratic 70 G. A. BAIG: Studies on dyeing wool with indigo, Tekstil 61 (1-6) 65-73 (2012.) and the maximum shade depth being peratures led to the formation of the fiber structure. During the experi- produced at temperature of 80 °C. wider temporary voids in the fiber mentation it was observed that tem- Heat is required to impart necessary structure through which the dye mo- perature above 100 °C severely da- kinetic energy to the polymer seg- lecules were diffused. Further increa- maged the wool fabrics and the dye ments of the fibers and dye molecu- se in temperature increased the seg- was precipitated as well. Temperature les. At lower temperatures the seg- mental mobility so high that dye mo- in the range of 60 to 70 °C could sa- mental mobility of polymer chains lecules were easily moved in and out fely be used to dye wool samples. was low so the pore sizes were of of the fiber structure. The net result The dyebath was subjected to HPLC very small dimensions. Higher tem- was less dye being accumulated in analysis to study the effect of tempe- rature. The following Fig.12 showed that higher temperature led to dye de- Reflection spectra vs. pH struction and hence less color stren- gth was achieved. 100 3.5. Effect of time 90 The following Fig.13 showed the ef- fect of dyeing time on color yield of 80 indigo on wool fibres. The results pH22 pH4 showed that color strength was high 70 4 n pH66 at the start and reached to equilibrium

io pH77 60 pH99 within 60 minutes but then started

e c t pH1111 l decreasing. It was concluded that in-

e f 50 digo had a very high strike rate on wool, however, as the time passed the %R 40 dye molecules started diffusing into the polymer matrix and so color 30 strength reached to equilibrium. Hi- 20 gher dyeing times led to the reduction in color strength which was probably 10 due to the over reduction of dye mo- lecules leading to the formation of 0 degradation products which did not 400 450 500 550 600 650 700 have substantivity for wool fibers. Wavelength (nm) High Performance Liquid Chromato- Fig.9 Colorimetric properties of indigo on wool as a function of pH graphy (HPLC) would be used to fur- ther investigate the hypothesis that longer dyeing time led to the forma- Colour strength analysis vs. pH tion of non-substantive products. 3.6. Build-up characteristics

20 The following Fig.14 showed the bui- 18 ld-up curve of indigo on wool fibres

) 16 at the mentioned process conditions. /S

(K 14 It could be seen that rate change of

th 12 color strength was high and only 1 % ng

re 10 o.w.f of indigo was sufficient to St achieve the maximum color strength. ur 8 lo Reflection spectra showed that maxi-

Co 6 4 mum absorption i.e. λmax of indigo on 2 wool was 660nm which was the same 0 when indigo was applied to cotton. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 The maximum absorption of indigo in dimethyl formamide (DMF) was at pH 610 nm. A higher absorption showed Fig.10 Colour strength as a function of pH that indigo dye molecules existed in G. A. BAIG: Studies on dyeing wool with indigo, Tekstil 61 (1-6) 65-73 (2012.) 71

Colour strength analysis vs. Sodium dithionite a different form in the wool matrix. It is known that indigo existed in the form of aggregates inside cotton 20 polymer and the absorption maxi- 18 mum was 660 nm. It was concluded

) 16 that indigo molecules were in the /S

(K 14 same state in wool polymer as well.

th 12 Fig.15 showed the Reflection spectra ng

re 10 and color coordinates of indigo on St 8 wool as a function of dye concentra- our l 6 Co tion. The color coordinates became 4 redder and yellower as the shade dep- 2 th was increased. Fig.16 showed the 0 reflection spectra of indigo during the 0 2 4 6 8 10 12 14 16 18 20 course of oxidation. Na2 S2 O4 (gpl) Fig.11 Colour strength versus sodium dithionite (shade 1 % owf, pH 6, 80 oC, LMR 3.7. pH vs. Fibre chemistry 40:1, 30 minutes) The following Fig.17 showed sche- matically the effects of acidic and alkaline pH on the chemistry of poly­ Colour strength analysis vs. Temperature peptide polymer chains. In the acidic region amine and amide groups were

21 protonated and therefore wool was safe while in the alkaline region ami- 18

) de groups were hydrolyzed. This /S 15 (K hydrolysis led to depolymerisation th

ng 12 and hence strength losses of the wool re

St fibres. The SEM analysis showed that 9 our l in the alkaline region wool fibres we­ Co 6 re severely damaged. Fig.17b showed 3 the schematic interactions of leuco

0 vat acid with wool. Wool has a lot of 40 50 60 70 80 90 100 110 amine, amide, sulphide and carbo-

Temperatureo(C) xylic groups and all of these posses polar nature from the chemistry Fig.12 Colour strength versus temperature (shade 1 % owf, pH 6, LMR 40:1, 30 viewpoint. The suggested substanti- minutes) vity of leuco vat acid toward wool was attributed to the hydrogen bon- Colour strength analysis vs. Time ding between the hydroxyl groups of leuco vat acid and the above mentio- ned wool functional groups. In the 20 oxidized form, indigo did not exhaust 18 while in the alkaline region these

) 16 hydroxyl groups were ionized. It was /S

(K 14 the acidic region in which hydroxyl

th 12 groups were preserved and imparted ng

re 10 the required substantivity to the dye St 8 molecules. our l 6 Co 4 3.8. SEM Analysis 2 The following Fig.18 from a) to f), 0 showed the effects of pH on the mor- 0 30 60 90 120 150 phology of wool fibres. The micro- Time (minutes) graphs showed that there were negli- Fig.13 Colour strength versus time (shade 1 % owf, pH 6, 80 oC, LMR 40:1) gible changes in surface morphology 72 G. A. BAIG: Studies on dyeing wool with indigo, Tekstil 61 (1-6) 65-73 (2012.)

Build-up of Indigo on Wool Reflection Spectra of indigo on Wool 25 100 0.1% owf 0.5% owf 1.0% owf 20 90 1.5% owf 2.0% owf 80 ) 15 70 (%

S 60 ce K/ an 10 50 ect

fl 40

Re 30 5 20 10 0 0 0.5 1 1.5 2 2.5 0 Shade (% owf) 400 500 600 700 Wavelength (nm) Fig.14 Build-up of indigo on wool (λmax 660nm)

Reflection Spectra of indigo during oxidation on wool Color Coordinates 100 -15 90 -8 -7 -6 -5 -4 -3 -2 -1-16 0 reduced indigo -17 intemediate b* 80 -18 intermediate -19

) 70 intermediate -20 intermediate (% 60 oxidized indigo a* ce

an 50 K/S vs. Chroma ect

fl 40

Re 28 30 21 S

20 K/ 14 7 10 0 Fig.1515 Colorimetric16 17 properties18 of19 in- 20 0 digo on wool asC* a function of 400 500 600 700 concentrations of dye Wavelength (nm) Fig.16 Reflection spectra of indigo during the course of oxidation

HO H N HO H N N H O H N H O O O H H NH O O O O CH3 H3C NH N NH CH NH CH3 3 H C H3C NH NH 3 NH NH O S H O SH O SH H O + H - H O H H2O OH 2 N

NH N NH2 2 HH O O O O N - H H O H N CH + O 2 3 + NH2 +CH3 OH H3C NH + NH H H3C NH2 NH2 - N O S + O SH2 N H NH + 2 NH3 OH a) b) Fig.17 Effect of pH: a) on wool fibers, b) on interaction between wool and dye molecules G. A. BAIG: Studies on dyeing wool with indigo, Tekstil 61 (1-6) 65-73 (2012.) 73

Chemist and Colorist 15 (1986) 6, 101-103 [2] Pierce J.H.: The indigo pheno­ menon: its history and application, International Dyer and Printer, 170 (1985) 7, 20 [3] Alpert. M.: Stonewash woollens, International Dyer 192 (2007) 10, 10 [4] Australian Wool Corporation, Australian Wool Classing, Raw Wool Services, 1990 [5] D’Arcy J.B.: Sheep and Wool Technology, NSW University Press, Kensington (1986) ISBN 0- 8684-0106-4 [6] http://www.wool.com.au/ attachments/Education/AWI_ WoolFacts.pdf. [7] Khan M.A. et al.: Natural dyeing on wool with indigo, and yellow dyes kamala, berberine, onion peel, amla, anar and palas in combination with indigo, Colourage 11 (2007) 54 (11), 54-56/58-60 [8] Martinková A. et al.: Dyeing of wool and cotton by natural dyes, Fig.18 SEM of wool fibres Texsci 2000 - 4th international con- ference : Liberec, Czech Republic, June 12-14, 2000, 432-435 and that wool fibres were stable in the ship with it. The dyeing pH should be [9] Bollhalder, E.: Dyeing with plant acidic region. Figures e and f showed in the acidic range and be monitored dyes and natural insect dyestuff, wool fibres treated in the alkaline re- strictly. Indigo molecules existed as DWI Reports 122 (1999) 28-39 [10] Baig G.A.: Indigo dyeing of Poly- gion. It was evident that alkalinity aggregates within the fiber matrix. ester (PET) – pH effects, Journal of caused severe damage to the wool The high dyeing temperature and the Textile Institute 102 (2011) 1, morphology. Since wool was dyed to alkaline conditions rendered severe 87-92 a good shade depth in the acidic re- damage to the wool fibres. The wool [11] Baig G.A.: Dyeing nylon with in- gion, there was nothing to worry fibers were damaged and became ten- digo in various pH regions, AU- about its degradation. dered in the alkaline region while TEX research Journal, 10 (2010) 1, indigo dye molecules were destroyed 21-25 4. Conclusion at 100 oC. Indigo had good build-up [12] South-eastern section, Effect of Wool fabrics were dyed with indigo on wool fibers. The shades became Dyebath pH on colour yield in in- digo dyeing of Cotton Denim Yarn, through exhaust technique in the ca- redder and yellower as the shade dep- Intersectional Paper competition, refully controlled pH conditions. The th was increased. Textile Chemist and Colourist 21 sodium dithionite concentration of 6 (1989) 12, 25-31 g/L is sufficient; when alkali is 0.6 References: [13] Instrumental Colour Measurement, g/L. When reducing agent had been AATCC Evaluation Procedure 6, optimized, the alkali concentration [1] Greer J.A., G.R. Turner: Indigo AATCC Technical Manual (2006) should have borne a certain relation- Denims: The Practical Side, Textile 386-391