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TECHNICAL REPORT

BUFFERING STABILITY OF DYEBATH IN DISPERSE/DIRECT

DYEING

Scientists of PCSIR Labs Complex Karachi.

M.Javaid Mughal, M.Naeem, Kamran Ahmed, Mohammad Aleem Ahmed, Mansoor Iqbal.

E-mail: javaidtextile@hotmail.com m_n_pearl@yahoo.com mansoorprocessing@hotmail.com

TEXTILE LABORATORY APPLIED CHEMISTRY RESEARCH CENTRE.

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TABLE OF CONTENTS

S.No. Topic Page No.

1 Introduction 1 2 Wet Processing

Pretreatment Dyeing Jet Dyeing Machines

Fully Flooded Jet Dyeing Machines

The dyeing process Buffer solution

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3 Visits of XYZ Processing Industry (Pvt) Ltd. First visit Second visit Third visit

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4 Result of collected Samples from XYZ Processing Industry (Pvt) Ltd. 8 5 Observation

In Jet no 11 Lot No. 385. In Jet no 6 Lot No 399.

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6 Preparation of Buffer Solution and their effect on Shades Buffer solution No. 1

Buffer solution No. 2 Buffer solution No. 3 Buffer solution No. 4 Buffer solution No. 5 Buffer solution No. 6 Buffer solution No. 7 Buffer solution No. 8

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7 Process Chart Proposed Process Chart

Desizing / Washing Process Chart Special Process (SP) Caustic Chart

Dyeing Process Chart

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8 Process Diagram Desizing

Desize Wash SP-Process (CAUSTIC) Disperse / Direct Dyeing

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9 Suggestions about Process Control 21

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SUMMARY A number of visits have been arranged by XYZ Processing Industry (Pvt) Ltd.and the problems

(particularly in the regard of pH stability of dyeing bath) were discussed with the management of

industry. After studying all the process and working conditions we have done initial study to solve

the problems which management of XYZ Processing industry were facing. In this preliminary

study we prepare different buffer solutions and dyed two sets of shade i.e. Olive and Beige, and

compared the results on same shade by using XYZ Buffer solution.

The corresponding colorimetric data for each dyeing with different buffer solution are displayed in

the attached sheets. By using buffer solution 1, 3 and 7 the values of K/S are higher than Buffer

Solution No. 8, which is of XYZ industry. A higher value of K/S means the higher depth of colour.

Similarly lower value of L* for the same buffer solutions also proves the results. The hue of these

solutions are also according to Munsell equation, having the lower value of a*. On the other hand

due to the higher value of a* the hue has considerably change for XYZ’s buffer solution. This high

value of a* may impart the fastness results also. By considering this data and on visual assessment

of shade, Buffer Solution No. 1,3 and 7 are found to be most suitable in terms of required shade

and also the chemicals used which ultimately reduced the production cost.

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Introduction:

Colour has been playing a dominant role in the life of man from time immemorial. Even in the

prehistoric times, the ancestors of man must have noticed (perhaps with or without understanding)

the abundance of multitude of colours worn by nature. Thus he must have wondered at the spread

of transient bright golden colour on the diffused clouds and on the landscape during dawn and

sunset, the “VIBGYOR” colours of a rainbow, the vast expanse of the blue sky on a cloudless day

or acres and acres of land crowned with chlorophyll dominated green coloured vegetation or even

an infinite variety of plants and trees, bearing flowers and fruits of varied colours of an almost

innumerable combination of yellow, red and blue hues in different depths and shades or even the

multi-coloured stripes and dots on the bodies of the birds of the sky, animals of the land and the

fish of the sea. With the growth of intelligence in man, he must also have noticed that most of the

colours he saw in nature (colours at sunset, flowers on plants etc.) were not permanent; the fading

of the colours of leaves changed to yellow or brown due to ageing, etc. There might have been an

urge in him to try to retain the pleasing colours for longer periods and working in this direction, he

might have found that certain plant juices and extracts from organisms produced colours which

would last long.

Textile is the backbone of Pakistan’s economy and shares more than 60% of the exports of

Pakistan. Cotton being the main crop in Pakistan attracts more attention, as it is still the principal

raw material for the textile industry in the world. Polyester is second important fiber used in textile

made up, as a pure as well as blends with cotton, Polyester cotton can be dyed with disperse and

direct dye.

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Wet Processing

Pretreatment: Pretreatment occurs immediately before dyeing/printing in the textile production chain, and

prepares the fabric for these processes. The fibers may either be in the form of yarn or a woven

fabric. Pretreatment normally occurs in the same facility as dyeing, often in the same machine

(integrated processing). A series of mechanical and wet treatments prepare the fabric in a verity of

ways. The nature and number of pretreatment stages depend upon both the fiber and the required

end result.

Dyeing:

Jet Dyeing Machines: The principle of using a jet of dye liquor to transport fabric in a dyeing machine was first patented

in 1961 by Burlington Industries of USA. In this system, the fabric is rotated at a very high speed

of about 400 meters per minute through a circular tube with the help of circulating dye liquor that

is collected from the bottom of the machine and passed through a powerful pump and a heat

exchanger to inject at the top of the machine. This equipment inspite of being much more

expensive than a winch became a success because it could dye textured polyester fabric, a craze at

that time, at 125° C. At this temperature, more rapid, well penetrated and better leveled dyeings

obtained which makes an economic sense. The Burlington patent was purchased by the US

machinery manufacturers, M/s. Gaston County and marketed the first jet machine in 1961.

However, the machine became popular only after 1968 when the market for polyester textured and

double jersey fabrics developed.

The principle of jet dyeing was a revolutionary idea among the hitherto existing dyeing machines.

As it often happens that once an idea is successfully established, many evolutionary developments

take place in rapid succession to improve the original invention. In the next decade, almost every

dyeing machinery maker marketed its own jet dyeing machine. It is not possible to give even the

salient features of all types of these machines and only principles of the more popular jets will be

discussed below.

Fully Flooded Jet Dyeing Machines:

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In the Gaston County Jet, fabric is lifted and circulated with the help of a powerful jet of liquor and

this tends to create longitudinal creases in the fabric. In order to reduce the tension, design of the

machine was modified to give the fabric an upward lift by filling the dyeing tube with the dye

solution. Machines have been patented having the dyeing tubes both in vertical and horizontal

positions and a number of tubes mounted side by side with a common pump and heater. Capacity

of each tube ranges between 100 to 150 kg and cloth movement speed varies from 100 to 200

m/min.

The dyeing process: When a disperse dye is added to the dye bath for dyeing a hydrophobic fiber such as polyester,

usually the dye is in excess of its solubility limit so that the dye is present in the dyebath in two

forms (1) Completely soluble and (2) Insoluble but finely dispersed, the relative amounts being

determined by the solubility of the dye in water at that temperature. When the fiber to be dyed is

entered into the dyebath, the dissolved dye slips molecule by molecule into the narrow pores

present in the fiber structure and gets attached there by certain forces. As a result, the concentration

of the dissolved dye in the dyebath decreases and with this decrease more and more dispersed dye

particles break up and go into solution, to be eventually absorbed by the fiber. Thus the dispersed

particles of the dye act as a reservoir, which replenishes the dyebath, when it is depleted by dyeing.

Since the dye has limited solubility in water, i.e., since it has an essentially hydrophobic nature,

there is an inherent tendency in the dissolved dye to leave the aqueous phase.

The dyeing of hydrophobic fibers with disperse dyes may be considered as a process of dye

transfer from a liquid solvent (water) to a solid organic solvent (Fiber) and the dyeing is considered

to take place in the following simultaneous steps:

1. Diffusion (Dispersion) of the dye in the solid phase into water by breaking up into

individual molecules.

2. Adsorption of the dissolved dye from the solution onto the fiber surface.

3. Diffusion of the adsorbed dye from the fiber surface into the interior of the fiber substance

towards the center.

Since the first step of dyestuff diffusion in the dye bath depends on the dispersibility and solubility

of dyestuff, further aided by the presence of dispersing agents in the dyebath and rise in

temperature. It is not influenced by the fiber characteristics. The second step of dyestuff adsorption

by the fiber surface is influenced by the solubility of the dye in the dyebath and that in the fibre.

Low solubility should necessarily reduce the rate of adsorption. However, the converse need not be

true, since the overall rate of dyeing is governed also by the third step of diffusion of the dye into

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the interior of the fiber. Under the normal dyeing conditions of time and temperature, the

adsorption rate is always higher than the diffusion rate (third step) and hence it is the third step that

governs the overall rate of dyeing.

When dyeing equilibrium is reached, the following subsidiary equilibria are also established.

1. Dye dispersed in the bath Dye dissolved in the bath.

2. Dye dissolved in the bath Dye adsorbed on the fibre.

3. Dye adsorbed on the fibre Dye diffused in the fibre.

The quality of dyeing is influenced by many factors, including the temperature and pH control. The

main objective for controlling the pH throughout the dyeing cycle is to permit the dye to produce

level and reproducible results. Colour reproducibility and the levelness of dye materials can be

ensured by pH control systems such as the use of a buffer system or a pH sliding system.

The use of buffer system requires a greater awareness not only of the factors that determine pH, but

also those that stabilize it against interferences. The pH of the water supply may vary or drift

during heating, and as a result a buffer system is required that resists the effect of such extraneous

influences. A buffer system is usually based on two chemicals, namely a weak acid and its

corresponding salts, such as acetic acid-sodium acetate. A pH sliding system is particularly useful

for non-migrating disperse dye on polyester. The controlled lowering of the pH can be achieved by

using products that release more acidic compounds as they undergo decomposition as the dyeing

temperature increases.

Buffer solution: A buffer solution is one that changes pH only slightly when small amounts of strong acid or a

strong base are added. Buffer solutions have many important applications in the industry.

A weak acid and its salt (conjugate base) the acetic acid –sodium acetate solution acts as a buffer

solution. One of the buffer components, the acid, is able to neutralize small amounts of OH-, and

the other, the base, is able to neutralize small-added amounts of H3O+.

pH = pKa + log [Conjugate base] [Weak Acid]

This equation for the pH of an acetic acid-acetate ion buffer is a special case of more general

equation, known as the Henderson-Hasselbalch equation.

Visits of XYZ Processing Industries (Pvt) Ltd.:

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First visit on 24th July 2007:

On first visit we met with the Director of XYZ Processing Industries (Pvt) Ltd. He pointed out the

problems of their textile industry in various departments of wet processing and about the

procedures of dyeing of blended fabric, consumption of chemicals and auxiliaries.

Second visit on 30th July 2007:

In our second visit of XYZ industry we observed the working procedures of wet processing. We

had checked their production parameters e.g. (machine parameter, chemical parameters, Fabric

parameters) and also observed all the processing in single lot of fabric step by step.

Photograph of XYZ Processing Industries (Pvt) Ltd.

Jet Machine for Desizing and SP-Process.

1. In the first step the grey fabric was desized. In Desizing process, the sizing material was

removed by the help of Desizing agent, ordinary well water was used in Desizing process.

§ Desizing agent: X gm

§ Wetting agent: Y gm

§ Salt: Z gm

§ Process time: 1hour

§ Machine temp: 80oC

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After 1 hr the Desizing process was completed, then desized fabric was washed with well

water in the same jet.

2. In 2nd step the special process in which caustic soda was used for the treatment of special

process.

§ Caustic soda: 10Kg/batch

§ Anti foam: 500gm/batch

§ Time:1hr 30min.

§ Temp:130oC

3. In third step the neutralization process takes place in the same jet, which was used in sp

process.

§ Sulphuric acid; 1Kg/batch

§ Wetting agent: 1Kg/batch

§ Temp: 80oC

§ Time: 30min.

After neutralization process the chemical was drained and jet was again filled with fresh

water, again run for 10min and unload the jet.

Photograph of Jet dyeing machine for Photograph of Jigger dyeing machine Disperse dyeing Direct dyeing and for topping of

Polyester/Cotton fabric

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4. In fourth step of wet processing, dyeing was carried out in jet dyeing machine at high

temperature. This is one bath dyeing for PC Blend. This process is high temperature dyeing

in jet dyeing machine.

§ Disperse dyes: X gm.

§ Direct dyes: Y gm.

§ Wetting agent: 1Kg

§ Leveler: 1Kg (200gm/Kg)

§ Acid: 2Kg ~ 4Kg.

§ Temp: 130oC

§ Heating time: 15min.

§ Cooling time: 30min.

Then washed with fresh well water.

5. Fifth step was hydroextraction. In this step water content of fabric was removed by high

speed spin hydro extractor machine.

In this visit we also collected the various samples of wet processing, which are.

1. Sample of grey fabric.

2. Sample of Sp process fabric.

3. Sample of neutralized fabric.

4. Sample of well water.

5. Sample of sp process waste water.

6. Sample of sp neutralized waste water.

7. Sample of dyeing waste water.

8. Sample of wetting agent.

9. Sample of (Sea salt- G-salt).

10. Sample of Buffer solution.

11. Sample of Acetic acid.

12. Sample of Sodium acetate.

13. Sample of dyes (Disperse and Direct dyes).

14. Sample of leveler.

15. Sample of HCl.

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Recipe of Buffer solution (According to Management)

Acetic Acid: 28%

Sodium Acetate: 10%

HCl : 6.2%

Remaining water: X %

Recipe of Buffer solution (According to Worker)

Acetic Acid: 24.4%

Sodium Acetate: 10.2%

HCl Acid: 14.2%

Remaining water: X %

Third visit on 13th August 2007:

In third visit we checked the pH of different processes.

PH of Sp waste water = 9.5

pH of SP neutralized waste water = 5.0

pH of dyeing solution before dyeing = 7.4

pH of dyeing waste water = 8.4

pH of well water = 7.5

Result of collected Samples from XYZ Processing Industries (Pvt) Ltd.

S.No. Name of Sample pH TDS Hardness Conc. Blend Ratio

1. Well water 7.9 922 ppm 338 ppm - -

2. Wetting agent 1% 2.9 - - - -

3. Company buffer Solution 0.5 - - - -

4. Sp Caustic waste water 9.3 - - - -

5. Sp neutralized waste Water 5.3 - - - -

6. Neutralized waste Water 7.1 - - - -

7. Dyeing waste water 7.9 - - - -

8. Sp neutralized fabric pH by extraction method

8.1 - - - -

9. % purity of Acetic acid - - - 96 % -

10. % purity of HCl Acid - - - 28.37 % -

11. Blend ratio of sp process (Caustic process) fabric

- - - - Cotton=20%

Polyester=80 %

12. Blend ratio of Neutralized fabric - - - - Cotton =19.75%

Polyester= 80.25%

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Observations:

In Jet no 11 Lot No. 385.

§ Workers did not maintain the temperature of Jet

§ Workers did not check the pH of dyeing solution.

§ No addition of salt in dyeing liquor.

§ No control of liquor ratio.

§ Jet was over loaded.

§ Workers did not maintain the process time.

In Jet no 6 Lot No 399.

§ Workers did not check the pH of dyeing solution

§ pH is out of range.

§ No control of liquor ratio.

§ Workers cannot maintain the level of water in jet.

§ Over dozing of leveling agent. Requirement was 1Kg but workers used 4Kg.

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Proposed Process Chart

Special Process (SP)

Caustic

Washing / Neutralizing Process

Hydro Extracting Process

Dyeing Process On High

Temperature

Hydro Extracting Process

Process Chart Diagram See Page # 16

Process Chart Diagram See Page # 17

Check pH of the Fabric

Desizing / Washing

Process Chart Diagram See Page # 15

Check pH of the Fabric

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Desizing / Washing Process Chart

Start

Fill Water L: R = 1:8

Set Nozzle Speed =

200 m/min

Load Fabric

Add Enzymatic Desizer 1-5 g/L

Wetting Agent 0.5-1 g/L Set pH = 5.0 Salt 1-5 g/L

Raise the Temperature Up to 80°C for 1 hour

Give Hot Wash on 100°C and check with

Iodine Solution

Drain Bath and Refill

OK

Not OK

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Special Process (SP) Caustic Chart

Fill Water L: R = 1:8

Set Nozzle Speed =

200 m/min

Load Fabric

Run for 5 minutes

Add Caustic as per Recipe 1 Kg /150 Kg Fabric.

Wetting Agent = 0.5-1 g/L Anti Foam = 0.5 g/L

Start Programme Raise the Temperature up to 130°C for 1 hour to

1½ hour

Start

Start Cooling at Programme End

Hot Wash and Add Acetic Acid for Neutralization

Check the pH= 7.0 of Fabric

OK

Cold Wash and Unload the Fabric

Hydro Extraction

END

Not OK

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Dyeing Process Chart

Fill Water L: R = 1:8

Set Nozzle Speed =

200 m/min

Load Fabric

Run for 5 minutes

Add Dispersing Agent or leveling agent = 0.5 g/L Wetting Agent=0.5-1 g/L

Adjust pH = 4.5 – 5.0 With Buffer Solution#1

Add Disperse and Direct

Dyes

OK Not OK

Start

Start Programme at 120°C or 130°C

Start Cooling at Programme

End

Take Sample at 80°C and add Salt=20 g/L

OK

Drain

Refill Bath 1000 Liter

Rinse Cold For

10 Minutes

Drain & Unload

END

Not OK

Hydro Extraction

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D E S I Z I N G PROCESS DIAGRAM

100 90 80 70 60 50 40 RT 0 10 20 30 40 50 60 70 80 90 100

TIME (IN MINUTES)

D E S I Z I N G WASHING DIAGRAM

100 90 80 60 40 RT 0 5 10 15 20 25

TIME (IN MINUTES)

80°C 60 Min Cooling

Water+Desizer+Detergent+Fabric+Salt

90°C HOT WASH 15 Minutes

Fabric+Water

TEMP (°C)

TEMP (°C)

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SP-PROCESS (CAUSTIC)

PROCESS DIAGRAM 140 130 120 100 80 60 40 RT

0 20 40 60 80 100 120 140 160 180

TIME (IN MINUTES)

Hold Time 90 min Cooling Gradient –4°C Rinse and Neutralize Gradient +2°C/min Add Caustic Water+Fabric

TEMP (°C)

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DESPERSE/DIRECT DYEING

PROCESS DIAGRAM 140 130 120 100 80 60 40 RT

0 10 20 30 40 50 60 70 80 90

TIME (IN MINUTES)

Hold Time 15 min depends on shade depth Cooling Gradient –4°C Add Sea Salt Hold 15 min Gradient +2°C/min Add Disperse/Direct Dyes Water+Fabric+Leveler

TEMP (°C)

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Suggestions about Process Control:

We have observed the whole jet dyeing processing area during number of visits and found that

there are some weaknesses in jet dyeing, SP process, dyeing equipment and processing techniques.

§ Industry shall provide the Standard pH stripes pH = 0-14 (Merck) to the each jet operator.

§ Industry shall abide by the process control chart and recipes.

§ Industry shall equip the jets with heat exchanger or solenoid valves for controlling the steam

and internal temperature of jet machine.

§ Industry shall equip the jets with the automatic graph control system.

§ Industry shall equip the jets with water gauge for correct filling of water and maintaining the

L: R as according to the standard conditions.

§ Operator shall check the pH after neutralizing with Standard universal indicator solution

pH = 0-14 (Merck) in SP process and finally unload the fabric.

§ Operator shall do the hydro extraction of fabric after SP-neutralization.

§ Hydrochloric and Sulphuric acid are hazardous for labors. Sulphuric acid also affects on the

cotton portions of PC blended fabric, it retards the cotton approximately about 0.25%. By the

use of excess Sulphuric acid, sulphate ions are formed, which also affects on the shade of

fabric.

§ Industry shall use provided buffer recipe no.1 in dyeing processing.

§ Operator shall maintain the pH of bath 4.5-5.0 and after that run; the color will be well mixed

with water and then run the color at approximately 40°C.

§ Operator shall check the pH of bath after running the Programme approximately after ½ hour

and finally before unloading the fabric.

§ Operator shall check the desizing efficiency of desized fabric with Iodine solution.

§ Industry shall purchase the Tegawa Scale for measuring the correct degree of Desizing.

§ Industry shall provide all pre weigh chemicals and dyestuffs to the jet operators.

§ Jet operators cannot change any parameters or recipe without consulting or intimating the

Management.