Indian Journal of Fibre & Textile Research Vol. 28, March 2003, pp. 94-99

Use of neem bark as wool colourant--Optimum conditions of wool dyeing

J P Mathur ', Anjula Mehtab, Romila KamawatC & C S Bhandari

Department of Chemistry, University of Rajasthan, Jaipur 302 004 , India

Revised received 23 October 2001; accepted 14 January 2002

Wool yam has been dyed with natural colourant extracted from the bark of neem (Azadirachta indica) branch lets under the optimum conditions. Neem bark colourant shows two absorption maxima at 275 and 374 nm. Dyeing of wool yam under the optimum conditions (pH, 4.5; colourant eonc., 0.05g per gram of wool; treatment time, 60 min ; and treatment temp., 97.5°C) shows very good light and wash fastness properties without deteriorating the quality of wool. The chemistry of wool dycing process has also been discussed.

Keywords: Colour fastness, Dyeing, Neem bark colourant, Tensile behaviour, U B solu bility, Wool

1 Int.-oduction The natural dyes, especially vegetable colourants,

have aroused considerable interest in dyeing of textiles due to their ecofriendly nature and harmful effect of synthetic dyes. Flowers of Gulmoher and Tessue, leaves of Teak and Henna, barks of Chir, Oak, Wattle, Madder, Manjeet and Ain trees, Berberine, Annato, Ratanjot, Lac, etc. are used for dyeing of wool , cotton, silk and synthetic fibres '·

'8.

However, the literature on the use of neem tree (Azadirachta indica) as colourant for dyeing of cotton fabric 19.20 is scanty and silent on its use for dyeing of wool.

In the present work, an attempt has been made to extract colourant from the bark of neem (Azadirachta indica) branchlets for its use in dyeing of wool yam.

2 Materials and Methods Two-ply worsted Bharat Merino wool yam (about

50 tex) was procured from the Central Sheep & Wool Research Institute, A vikanagar, Rajasthan and used for study.

All the chemicals used were of Analar or equivalent quality.

• To whom all the correspondence should be addressed. Present address: Division of Textile Manufacture & Textile Chemistry, Central Sheep & Wool Research Institute, Avikanagar, 304 501, India Phone: 2201 79; Fax: 0091-01437-220163; E-mai l: jpmathur@cswri.raj.nic.in b Present address: Department of Chemistry, Govt. College, Pali, Rajasthan, India C Present address: Department of Chemistry, Vedik Kanya P G College. Raja Park, Jaipur, Rajasthan, India

2.1 Scouring

Scouring of yarn was carried out as per the standard procedure21 in four bowls at 48±2°C using the material-to-liquor ratio at 1: 100. The first three bowls contained appropriate quantity of scouring solution [2.0 g Na2C03 and 1.0 mI non-ionic detergent (U ltravan JU) per litre of solution] while the fourth bowl contained only water. Dritd yarn at room temperature was treated with ethanol in soxhlet apparatus for 3 h at the rate of 6 siphons/h to ensure removal of residual soap and to facilitate the maximum penetration of dye molecules into the wool fibre. The yarn was then rinsed with distilled water and finally dried at room temperature.

2.2 Extraction of Colourant

The neem tree branchlets left after grazi ng of leaves by sheep in the campus of Central Sheep & Wool Research Institute, Avikanagar, were collected, chopped with steel knife and dried at room temperature. The chopped bark of neem tree branch lets was washed with a solution of Na2C03 (2.0 gIL), rinsed with distilled water and dried at room temperature. The dried bark was crushed and powdered so as to pass through a sieve 20 (number of holes/cm\

The bark powder (lOOg) was soaked overnight in distilled water (1000 ml) and then boiled for optimum extraction time21 (120 mjn.) . The contents were filtered and the filtrate was concentrated under reduced pressure on rotatory vacuum pump at 60°C. The neem bark colourant contains gum and mucilage.

MATHUR et al.: USE OF NEEM BARK AS WOOLCOLOURANT 95

These are not soluble in water on drying and produce the bead on dyed material, which on rubbing produces stains. These impurities were removed by treating the concentrate with 100 ml of ternary solvent mixture [acetone: methanol: water, 40:30:30 (v/v)] by constant shaking for 1 h. The contents were filtered and the filt rate so obtained was concentrated and dried under reduced pressure on rotatory vacuum pump at 40°C.The dried mass (neem bark colourant, abbreviated as NBC) was found to be 99.0 % soluble in water.

A stock solution was prepared by dissolving i.O g NBC per 100 ml solution. The NBC solution showed two absorption maxima at 275 and 374 nm on Carlzeiss spectrophotometer (Model VSU 2P).

2.3 Optimum Dyeing Conditions

The optimum dyeing conditions, namely treatment temperature, acid conc., NBC conc., treatment time and pH, were determined by dyeing the scoured wool yarn in boiling aqueous solution.

2.3. t Treatment Temperature

All the experiments were performed at 97.5°C (boil ing aqueous solution) because at this temperature sufficient heat energy is available from boiling water.

2.3.2 Selection of Acid

Acetic acid was selected for all experiments on the basis of physico-chemical studies as described elsewhere21

.

Scoured yarn (10 g) was treated separately with acetic acid (1000 ml) at pH 2.5, 4.5 and 6.5 for 60 min at boil. The acid-treated yarns were washed with appropriate quantity of washing solution [2.0g Na2C03 and 1.0 ml non-ionic detergent (Ultravan JU) per liter of solution], rinsed with distilled water and finally dried at room temperature.

2.3.3 Concentration of Colourant

The optimum concentration of neem bark colourant (NBC) required for dyeing of wool was determined by dyeing of yarn at pH 4.5. Eight different concentrations of neem bark colourant, viz. 10, 20, 30, 40, 50, 60, 70 and 80 ml, were selected from the stock solution of the colourant in 8 different dye baths, each containing 50 ml potassium hydrogen tartrate (0.2 g per 109 wool yarn) and acidulated water (pH 4 .5) to mai ntain the material-to-l iquid ratio at I: 100 (w/v). The washing solution and blank solutions were prepared as usual. AlOO ml blank

solution contains 0.2 g potassium hydrogen tartrate per 109 wool yarn and 2.0 ml glacial acetic acid.

The eight samples of scoured yarn were soaked in acidulated water (pH 4 .5) for nearly 30 min and then dyed separately in different dye baths (pH 4.5) having above-mentioned different concentrations of NBC at 97.5°C (boiling aqueous solution) for 60 mill. The loss of water was maintained by adding hot acidulated water (pH 4.5) from time to time to the dye bath. The exhaustion of the each dye bath solution was recorded before and after dyeing of yarn at 374 nm against blank solution. The dyed yarn was taken out and washed with appropriate quantity of washjng solution, rinsed with distilled water and finally dried at room temperature.

The following relationship was used to calculate the percentage exhaustion of the dye bath :

Exhaustion Exhaustion

% NBC absorbed = before dyeing after dyeing x 100 ... (I ) Exhaustion before dyeing

Fig. 1 reveals that 5 g of NBC is required for dyeing 100 g of yarn.

2.3.4 Treatment Time

The scoured yarn (j 0 g) was soaked for nearly 30 min in acidulated water (5.0 ml glacial acetic acid per 100 ml of solution, pH 2.5) and then subjected to dyeing for different intervals of time, viz. 20, 40, 60, 80, 100 and 120 min, at 97.5°C in a dye bath containing 50 ml NBC (stock solution), 50 ml sol ution of potassium hydrogen tartrate (0.2 g), 50 ml

<5 o ~ >-.44 .0

"0 Q/

-f' o III .0 o

~42 z:

";!?

40~ __ ~ __ ~ ____ ~ __ ~ __ -L __ ~ ____ ~ __ ~

10 30 ~o 70 90 Volume of 1·0 % stock solution, ml

Fig.l--Necm bark colourant absorbed by wool at different concentrations

96 INDIAN J. FIBRE TEXT. RES ., MARCH 2003

glacial acetic acid and distilled water so as to make (material-to-liquor ratio, I: 100) total volume 1000 ml in dye bath. The loss of water was maintained by adding hot acidu lated water (pH2.5) from time to time to the dye bath. The exhaustion of the dye bath solution was recorded before and after dyeing of yarn at 374 nm against blank solution. The dyed yarn was taken out, washed with appropriate quantity of washing solution, rinsed with distilled water and finally dried at room temperature.

The above procedure of dyeing was repeated at pH 3.5, 4.5, 5.5 and 6.5 under the identical conditions using 30, 20, 10 and 0.6 ml acetic acid instead of 50 ml g lacial acetic acid per 100 ml in dye bath as well as in blank solutions for respective pH .

Using Eq. (I), it is revealed that as the treatment time increases in dyeing process the exhaustion of neem bark colourant increases up to 60 min and then it becomes constant.

2.3.5 pH The above procedure of dyeing was repeated at pH

2.5, 3.5, 4.5, 5.5 and 6.5 under identical conditions for 60 min. Using Eq. (I), it is revealed that as the pH of dye bath increases the percentage of neem bark colourant absorbed by wool decreases.

2.4 Physico-chemical Studies The colour strength in terms of KIS values, colour

fastness, urea-metabisulphite solubility and tensile be­haviour have been studied by the well-known methods.

2.4.1 Estimation of Colour Strength

Scoured wool yarns dyed at different pH, namely 2.5, 3.5, 4.5, 5.5 and 6.5, were subjected to estimation of colour strength in terms of KIS values on Computer Colour Matching Instrument Jaypak 2300. The results are shown in Table I.

2.4.2 Colour Fa~tness Tests

The dyed yarns were subjected to testing for their abi lity to withstand li ght and wash fastness as per the BIS methods IS: 2454-1967 and IS: 687-1979 respectively.

Shirley development light fastness tester (SOL 237) was used to test the dyed yarn. The instrument was adjusted to expose the dyed samples and blue wool standards (rating 1- 8) for 5, to, 20 and 40 h at 65 ± 5 % RH. The exposed dyed samples and blue wool standards were compared after the exposure.

The dyed yarn was converted into knitted form measuring 100 mm x 40 mm. It was then subjected to wash fastness test in a Launder-O-meter using 5.0 g per litre of soap (Lisapol 0 paste) at 50 ± 2°C for 30 min. The sample was compared with gray scale rating (1-5) as per the BIS method . The resu lts of light and wash fastness are shown in Table 1.

2.4.3 Determination of Urea-metabisulphite Solubility

The solubility of experimental wool yarns was determined by using oven dry weigh ts of 1.0 g wool before and after its solubility in 100 ml urea­metabisulphite solution as per the fo llowing standard procedures:

2.4.3.1 Sampling and Oven Dry Weight The experimental yarns were cut in 1.0 cm size

and four samples (l.Og each) of each experimental yarn were taken for the determination of solubility in urea-metabisulphite solution . One sample was dried down to constant weight at 105 ± 2 °C in an electric oven in order to determine the oven dry weight of experimental samples.

2.4.3.2 Preparation of Urea-metabisulphite Solution

For treatment of 1.0 g wool yarn sample, 50 g urea was dissolved in 50 ml hot distilled water. Sodium

Table 1- Physico-chemical properties of yarn dyed with neem bark eolourant

pH Physico-chemical properties

Colour strength Colour fastness U B solubility Tensile strength

KIS Light Wash % Tenacity Extension-at- break g/tex %

2.5 3.972 3-4 3 35.37 6.39 14.9

3.5 3.8 19 3-4 4 30.40 6.43 14.7

4.5 3.509 3-4 4 29.75 6.58 14.0

5.5 3.305 3-4 3-4 23.60 6.47 14.6

6.5 2.742 3-4 3-4 20.80 6.46 14.8

Scoured 1.325 31.62 7.27 13.9 yarn

MATHUR er al.: USE OF NEEM BARK AS WOOL COLOURANT 97

metabisulphite was dissolved in 10 ml of warm water. The two solutions were then cooled to room temperature and mixed. About 2.0 ml of 5 N sodium hydroxide solution was then add to thi s mi xture so as to adjust the pH of the sol uti on at 7±0.1. The resulting solution was made up to 100 ml by add ing di stilled water.

2.4.3.3 Preparation of Urea Solution

F:or wash treatment of 1.0 g wool yarn sample, 25 g urea was dissolved in about 25 ml of hot di stilled water and the solution was cooled to room temperature and made up to 100 ml by adding distilled water.

2.4.3.4 Procedure

The urea-metabi sulphite solution (100 ml ) was taken in each of the three pyrex glass tubes of 200 ml capacity . The tubes were then placed in water bath at constant temperature of 65± 2°C. The water level in the bath was adjusted so that it remained nearly 5 cm above the urea-metabisulphite (U B) solution inside the tube. When the U B solution attai ned bath temperature of 65±2°C, the yarn samples were immersed in the solution of respective tubes . The tubes were then closed tightly with stoppers and gently shaken till the yarn got completely wetted. The tubes were shaken gentl y after regular interval of 15 min for a total period of 60 min . The contents of the tube were then transferred to a pre-weighted (oven­dried) si ntered G- l crucible, and washed first with hot distilled water and then with urea solution . The washing with urea solution was repeated three times and the contents were then thoroughly washed with hot distilled water (about 60 °C) for six times. The residue in the sintered G-l crucible was dried in an electric oven at 105± 2°C for 6 h and then cooled in a desiccator to room temperature. The process of drying and weighing was repeated till a constant weight was obtained.

The above testing was conducted for both the scoured yarn and the yarn treated with acetic acid at pH 2.5, 4.5 and 6.5. The resu lts are shown in Tables I ancl 2.

2.4.4 Tensile Behaviour

The yarns dyed earlier at clifferent pH, viz. 2.5, 3.5, 4.5, 5.5 and G.5, were subjected to tens ile testing on Uster automatic single yarn strength tester (Zewlleger) with 600 g measuring load under standard conditions of relative humidity (65 ± 5 %) and temperature (27 ± 2°C). The above testing was

Table 2- Physico-chemica l properties of experimental yarns

Yarn pH Phys ico-chemical properties

UB Tenacity Elongation-at- break solubi lit y g/tex %

%

Scoured 31.62 7.27 13.9

Acet ic acid 2.5 38.96 6 .1 8 13.8

treated 4.5 26.89 6.35 11.9

yarn 6.5 2 1.66 6.28 11.7

Dyed yarn 2.5 35.37 6.39 14.9

(Acetic aeid 4.5 29.75 6.58 14.0

and NBC) 6.5 20.80 6.46 14.8

Comparative data

Acetic acid 2.5 +7 .034 - 1.09 -0. 1

treated 4.5 -4.73 -0.92 -2 .0

liS 6.5 -0.996 -0.99 -2.2

scoured yarn

Dyed yarn 2.5 +3 .75 -0.88 + 1.00

liS 4.5 - 1.87 -0 .69 +0. 10

scou red yarn 6.5 - 10.82 -0.8 1 +0.90

Dyed yarn 2.5 -3.59 +0.21 +1.1

liS 4.5 +2.86 +0.23 +2.1

acetic acid 6.5 -0.86 +0.18 +3 .1

treated yarn

NBC- Neem bark colourant

conducted for the scoured yarn treated with acetic acid at pH 2.5, 4.5 and 6.5. The results are shown in Tables 1 and 2.

3 Results amI Discussion Tree bark chiefly contains 13-15 % H20, 3.43 %

protein , 0.68 % alkaloiJs, 4-16 % minerals, 5-8 % tannin, ancl 5-9 % gum and mucil age22

.23 NBC

contains cl uster of compounds instead of single compound. Some of them, such as flavo nes and rel ated compounds, have been isolated, characterized and reported in literature24

.25

. Flavones have several bindi ng sites (Fig. 2) and its structure in no way represents any compound present in neem bark.

The NBC molecules mi grate from the so lution to the surface of the fibre by means of transport energy available due to increase in temperature of the bath solution, get adsorbed on the ~urface and diffuse through swollen pores into the interior of the fibre. The neem bark colourant is retained by the wool due to the interaction between NBC and wool as well as by non-polar van der Waal's forces.

98 INDI AN J. FIBRE TEXT. RES. , MARCH 2003

I

5 OH

HO OH

OH 0 Fig. 2 - Flavoncs (ncem bark constituent)

/ ",/ " HN NH HN NH

" / \ / CI-!, CI-12-S-S-CI1 2.L·11 ---7 C1 I. CI-I2-S-C I1 2.CH

/ \ / "-CO OC CO DC " /" ,/

Fig. 3-- Formation of ncw Monosu lphidc cross- linkagcs

During dyeing process, wetting causes swelling of woo l by break ing hydrogen bo nds and weakening of ionic linkages among polypeptide chains . At thi s stage, the activation of the asparti c ac id and g lutami c aci d res idues of wool prote in occurs in the pH range of 2.5 - 6.5. In thi s pH range, wool prote in (aspartic/ g lutami c ac id residue) loses hydrogen io ns, leavi ng ioni zed carboxy l groups; the pos iti ve charge increases on lys ine/argini ne resid ue of the wool. T hese positi ve charge centres on the woo l (-NH Jt

) serve as attracti ve force fo r colourant bearing negati ve charge.

The yarns dyed at pH 2.5, 3.5 , 4.5, 5.5 and 6.5 exhibit redd ish brown characte ri s ti c colou r. As the pH of the dye bath increases fro m 2.5 to 6.5, the colour strength in terms of K/S value decreases from 3.972 to 2.742. T hese yarns show li ght and wash fastness ratings o f 3-4. However, the wash fas tness rat ing of the dyed yarn was fo und least when dyed at pH 2.5 and maximum at pH 3.5 and 4 .5 (T able 1). In other words, the yarn dyed at pH 2.5 bleeded more colour during washing as compared to the yarn dyed at other pH. T hi s may be due to the spo ntaneous attraction of colourant ani ons by positively charged centres o f wool. These colourant ani ons perhaps get accumulated in the orthocortical cel ls and come out eas ily during washing. This is supported by the fact that the rate of di ffusion o f the dye into o rthocort ical cell is three times greater than the rate of diffusion of the dye into the paracortica! cell s26

.27

.

T he NBC molecules which are not held by ortho­and para- cortical ce ils are released d uring washing by

detergent action. At pH 4 .5, wh ich is close to isoelectric point of wool , the swelling action of wool is minimum. At this pH, very few posi tive absorption sites are avail able for NBC anion . Both migratio n and diffusion of NBC molecules are mini mized at thi s pH . Thi s results in uniform di stributio n o f NBC molecules o n wool and almost no bleeding occurs.

As the pH increases beyond 4.5 , the swe lling action of wool increases, poss ibly due to the degradation o f o rthocortical ce lls. The NBC mol ecules in large number enter into fibre th rough swo llen pores. These molecules poss ibly could not be reta ined into the corti cal ce ll s due to the repul sion between NBC anion and carboxy lic ani on o f g lutamic and asparti c acid res idues, consequently the hleed ing o f colour occurred during washing.

The solubility of wool in urea-metabisulphi te solution decreases as the pH of the dye bath increases. Thi s may be due to the decreas ing tendency of shortening of po lypeptide chains on account of ac id hydrolysis of wool and the increas ing tendency of rup turing o f d isulphide linkage and fo rmation o f new cross- linkage of monosulphide type, an insolu ble lan thi onine resid ue (Fig. 3).

Tabl es I and 2 shows that the U B so lubility of the dyed yarn at pH 3.5 and 4 .5 is more close to that of scoured ya rn . T his ind icates that there is a least damage in wool on dyeing in the pH range 3.5 -4.5 .

It is observed fro m Table I that with the increase in pH the tenacity of the dyed yarn increases up to pH 4.5 and then decreases but the ex tension-at-break decreases up to pH 4.5 and then increases. This may be due to the dyeing effects occurred during dyei ng treatment. During dye ing process, some bonds are weakened and consequentl y the dyed yarn can easil y be stretched with low load in comparison to the undyed or scoured yarn which resul ts in low tenac ity and high extension-at­break for the dyed yarn vi s-a-vis scoured yarn .

T he compar:1tive data, such as (i) ac id-treated yarn vs scoured yarn , (ii ) yarn dyed at di fferent pH vs scoured yarn , and (iii ) yarn dyed at different pH vs acid-treated yarn (T able 2), indicate that the aceti c acid causes maximum damage to the wool yarn. But the damage is reduced signi ficantly when the scoured yarn is treated with acet ic acid and BC under the identical conditions. In other words, the use of NBC not o nly minimizes the damage in the wool fibre but also improves its quality. This may be due to the fo rmati on of new linkages between NBC and polypeptide chains o f wool. T hese new linkages poss ibl y offer res istance in rupturing the bonds and

MATHUR et al.: USE OF NEEM BARK AS WOOL COLOURANT 99

reduce the formation of lanthionine contents, and thus protect the polypeptide chains.

4 Conclusions The extraction of neem bark colourant from neem

tree branch lets takes 120 min for its optimum extraction. Solubility of neem bark colourant in water is improved by treating it with the ternary mixture of solvents acetone, methanol and water in the volume ratio 40:30:30. The neem bark colourant obtained from looped branchlets of neem tree is ecofriendly since no harm to green vegetation is done as the neem tree branchlets are looped as an essential need for its natural growth and these branch lets are used as fodder and fuel.

The soft, lustrous, reddish-brown colour with good fastness on wool without deterioration in physico­chemical properties of yarn can be obtained on dyeing

at 97.5°C (boiling aqueous solution) under the optimum conditions [pH 4.5 (acetic acid), neem bark colourant conc. , 5% (on the weight of yarn), and treatment time, 60 min.]. Further, the di scharge of effluent will not harm the environment since it does not contain any polluting ingredients.

Acknowledgement The authors are thankful to the Head, Department

of Chemistry, University of Rajasthan, for providing facilities for conducting research work. One of the authors (JPM) is grateful to the Director, Central Sheep & Wool Research Institute, Avikanagar, for granting study leave, extending the facilities for physico-chemical testi ng and supplying of Bharat Merino wool yarn .

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