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Dyeing of Polyester Fabric with Disperse Dyes

Experiment Name: Dyeing on Polyester fabric with Disperse dyes. Introduction: Dyes are coloured, unsaturated organic chemical compounds capable of giving colour to a substrate (a textile),i.e. colouring or dyeing it.

The term “disperse dye” have been applied to the organic colouring substances which are free from ionizinggroups, are of low water solubility and are suitable for dyeing hydrophobic fibres. Disperse dyes havesubstantivity for one or more hydrophobic fibres e.g. cellulose acetate, nylon, polyester, acrylic and othersynthetic fibres.

The negative charge on the surface of hydrophobic fibres like polyester can not be reduced by any means, sonon-ionic dyes like disperse dyes are used which are not influenced by that surface charge.

History of Disperse dyes:

In 1922, Green and Saunders made one type of coloured azo compound, in which a solubilizing group (forexample- methyl sulphate, -CH2-SO3H) is attached to amino group. In dye bath, they are slowly hydrolyzed andproduce azo compound and formaldehyde bi sulphate. This free azo compound was capable of dyeing celluloseacetate fibres. This dye was named “ionamine”. But this ion amine did not give satisfactory result in dyeing.

Later in 1924, Baddiley and Ellis produced sulpho ricinoleic acid (SRA) for dyeing acetate fibres. This SRA wasused as dispersing agent. Later it was seen that SRA was capable of dyeing Nylon, polyester, acrylic etc. In 1953this dye was named as “Disperse Dye”.

Properties of Disperse Dyes:

Ø Disperse dyes are nonionic dyes. So they are free from ionizing group. Ø They are ready made dyes and are insoluble in water or have very low water solubility. Ø They are organic colouring substances which are suitable for dyeing hydrophobic fibres. Ø Disperse dyes are used for dyeing man made cellulose ester and synthetic fibres specially acetate andpolyester fibres and sometimes nylon and acrylic fibres. Ø Carrier or dispersing agents are required for dyeing with disperse dyes. Ø Disperse dyes have fair to good light fastness with rating about 4-5.

Classification of Disperse Dyes:

According to Chemical Structure: 1.Nitro Dyes 2.Amino Ketone dyes 3.Anthraquinonoid dyes 4.Mono azo dyes 5.Di- azo dyes

Application Methods of Disperse Dyes:

1.Method N: Normal dyeing method. Dyeing temperature is 80-100°C. 2.Normal NC method: Method of dyeing at normal temperature with carriers. Dyeing temperature 80-100°C. 3.Method HT: High temperature dyeing method. Dyeing temperature 105-140°C. 4.Method T: Thermasol dyeing method. Dyeing temperature 180-220°C, continuous method of dyeing.

5.Pad roll method: Semi continuous dyeing method. 6.Pad steam method: Continuous dyeing method.

Dyeing Mechanism of Disperse Dye:

The dyeing of hydrophobic fibres like polyester fibres with disperse dyes may be considered as a process of dyetransfer from liquid solvent (water) to a solid organic solvent (fibre).Disperse dyes are added to water with asurface active agent to form an aqueous dispersion. The insolubility of disperse dyes enables them to leave thedye liquor as they are more substantive to the organic fibre than to the inorganic dye liquor. The application ofheat to the dye liquor increases the energy of dye molecules and accelerates the dyeing of textile fibres.

Heating of dye liquor swells the fibre to some extent and assists the dye to penetrate the fibre polymer system.Thus the dye molecule takes its place in the amorphous regions of the fibre. Once taking place within the fibrepolymer system, the dye molecules are held by hydrogen bonds and Van Der Waals’ force.

The dyeing is considered to take place in the following simultaneous steps:

Diffusion of dye in solid phase into water by breaking up into individual molecules. This diffusion depends ondispersibility and solubility of dyestuff and is aided by the presence of dispersing agents and increasingtemperature.

Adsorption of the dissolved dye from the solution onto the fibre surface. This dyestuff adsorption by fibre surfaceis influenced by the solubility of the dye in the dye bath and that in the fibre.Diffusion of the adsorbed dye from the fibre surface into the interior of the fibre substance towards the centre. Innormal condition, the adsorption rate is always higher than the diffusion rate. And this is the governing step ofdyeing.

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

Dye dispersed in the bath

Dye dissolved in the bath

Dye dissolved in the bath

Dye adsorbed on the fibre

Dye adsorbed on the fibre

Dye diffused in the fibre

Effect of Various Conditions on Disperse Dyeing:

Effect of Temperature:

In case of dyeing with disperse dye, temperature plays an important role. For the swelling of fibre, temperatureabove 100°C is required if high temperature dyeing method is applied. Again in case of carrier dyeing method,this swelling occurs at 85-90°C. If it is kept for more time, then dye sublimation and loss of fabric strength mayoccur.

Effect of pH:

For disperse dyeing the dye bath should be acidic and pH should be in between 4.5-5.5. For maintaining this pH,generally acetic acid is usedAt this pH dye exhaustion is satisfactory. During colour development, correct pHshould be maintained otherwise fastness will be inferior and colour will be unstable.

Carrier Dyeing Method:Procedure:

1. At first, a paste of dye and dispersing agent is prepared and then water is added to it.

Dyeing Curve

Dyeing Curve

2. Dye bath is kept at 60°C temperature and all the chemicals along with the material are added to it. Thenthe bath is kept for 15 min without raising the temperature.

3. pH of bath is controlled by acetic acid at 4-5.5.

4. Now temperature of dye bath is raised to 90°C and at that temperature the bath is kept for 60 min.

5. Then temperature is lowered to 60°C and resist and reduction cleaning is done if required. Reductioncleaning is done only to improve the wash fastness.

6. Material is again rinsed well after reduction cleaning and then dried.

High Temperature Dyeing Method:Procedure: Ø At first a paste of dye and dispersingagent is prepared and water is added to it.Ø PH is controlled by adding acetic acid. Ø This condition is kept for 15 minutes attemperature 60°C. Ø Then the dye bath temperature is raisedto 130°C and this temperature ismaintained for 1 hour. Within this time,dye is diffused in dye bath, adsorbed bythe fibre and thus required shade isobtained. Ø The dye bath is cooled as early aspossible after dyeing at 60°C. Ø The fabric is hot rinsed and reduction cleaning is done if required. Ø Then the fabric is finally rinsed and dried.

Thermasol Dyeing Method:

Dyeing of Polyester Fabric inThermasol Dyeing Method

Thermasol method is continuous methodsof dyeing with disperse dye. Here dyeingis performed at high temperature like 180-220°C in a close vessel. Here time ofdyeing should be maintained very carefullyto get required shade and to retainrequired fabric strength.

Sequence: Pading-Drying-Thermofixing-AftertreatmentProcedure: Ø At first the fabric is padded with dye solution using above recipe in a three bowl padding mangle. Ø Then the fabric is dried at 100°C temperature in dryer. For dyeing, infra red drying method is an ideal methodby which water is evaporated from fabric in vapor form. This eliminates the migration of dye particles. Ø Then the fabric is passed through thermasol unit where thermo fixing is done at about 205°C temp for 60-90seconds depending on type of fibre, dye and depth of shade. In thermasol process about 75-90% dye is fixed onfabric. Ø After thermo fixing the unfixed dyes are washed off along with thickener and other chemicals by warm water.

Then soap wash or reduction cleaning is done if required. And finally the fabric is washed .

Conclusion :

By this experiment we have acquired so much knowledge about disperse dye.we have known too much end usesof disperse dye. 0 1 0 0 1 929