Presentation on: Dyeing of Cotton with Reactive Dye

Prepared By:Tanvir Ahammed Rana

Id. 201200040003819th Batch, Textile Department.

SouthEast University.

Introduction

Reactive dyes are probably the most popular class of dyes to produce 'fast dyeing' on piece goods. These were first introduced a little over 40 years based on a principle which has not been used before. These dyes react with fibre forming a direct chemical linkage which is not easily broken. Their low cost, ease of application, bright shades produced by them coupled with good wash fastness make them very popular with piece good dyers. Even in threads these classes are gaining in popularity for cotton sewing.

TheoryA dye which is capable of reacting chemically with a substrate to from a covalent dye-substrate linkage is known as a reactive dye. Here the dye contains a reactive group and this reactive group makes covalent bond with the fibre polymer and act as an integral part of fibre .This covalent bond is formed between the dye molecules and the terminal –OH (hydroxyl) group cellulosic fibres or between the dye molecules and the terminal amino (-NH 2) group of polyamide fibres. The general formula of reactive dye can be written as following:

D-X-Y Here,

D=Dye part( colour producing part).

X=Bridge.

Y=Functional group.

D-X-Y+ Fibre = Fibre covalent bond.

History of dyestuff

The historical development of the synthetic dyestuffs dates back to 1856, when eighteen year old, W.H. Perkin discovered the synthesis of Mauveine, a basic dye, by accident, while he was engaged in the study of the action of potassium dichromate on aniline Sulphate. He successfully converted the process he had developed in laboratory to a large-scale production, and demonstrated the application of the dye on silk. The intermediates nitrobenzene and aniline required in the production were also made commercially by him. Nitrobenzene was earlier prepared by Mansfield in 1847.

Definition of dye

A dye is a coloured organic compound that absorbs light strongly in the visible region and can firmly attach to the fiber by virtue of chemical and physical bonding between group of the dye and group on the fiber. To be of commercial importance a dye should be fast to light, rubbing and water. Colour and dye have always played an important role in the life of man from time immemorial.

Cellulosic fibersThe earliest cellulosic fibres were lines and cotton, both of which have been used since remote antiquity. Linen, or flax, is derived from ‘bast’ fibres of plants of the Linum family, especially Linum usitatissimum. After removal of glutinous and pectinous matter the fibre has cellulose content of 82 – 83%. Cotton, which is fine hair attached to seeds of various species of plants of the Gossypium genus, has a cellulose content which may reach 96%. Cellulose is a polymer of high molecular weight consisting of long chains of D-glucose units connected by B-1, 4- glucosidic bonds, and its structure may be represented as follows:

Each glucose unit contains three alcoholic hydroxyl groups, of which two are secondary and one is primary. The degree of polymerization of cellulose varies from a few hundred to 3500 or more.

Cotton

Cotton was considered a luxury fabric, as it was imported all the way from India and usually dyed or painted before it was shipped. Cotton was also valued because of the brightness and colorfastness of the dyes used to color it, and also for its use in making candlewicks. Samples of cotton fabrics have been found in India and Pakistan dating to 3000 BCE, but it did not appear in Europe until the 4th century. Cotton waving establishments were formed in Italy in the 13th & 14th centuries but they did not make a significant economic impact on the industry as they produced a coarser quality of fabric than the imported fabric, and therefore had difficulty in obtaining a good supply of cotton fiber.

Properties of reactive dye1. Reactive dyes are anionic dyes which are used for dyeing cellulosic protein

polyamide fibres.

2. Reactive dyes are found in powder, liquid and print paste from.

3. During dyeing, the reactive group of this dye forms covalent bond with fibre polymer and becomes an integral part of fibre.

4. Reactive dyes are soluble in water.

5. They have very good light fastness with rating about 6.

6. The dyes have very stable electron arrangement and the degrading effect ultraviolet ray.

7. Reactive dyes give brighter shads and have moderate rubbing fastness.

8. Reactive dyes are comparatively cheap.

9. Reactive dyes have good perspiration fastness with rating 4-5.

10. Fixation occurs in alkaline condition

Assistants used for dyeing with reactive dyes

Salt: As a salt, NaCI is used widely. The salt end the following things:1. Salt are used to increase the affinity of dye to fibre. 2. It decreases the hydrolysis rate of dyes. 3. It neutralizes the electro negativity of fibre surface when immersed in solution. 4. It puts extra energy to push dye the fibre polymer ie increase absorption. The amount of salt used depend upon the shade to be produced- For light shade -10-20 gm/litre salt is used. For medium shade-30-50 gm/litre is used. For deep shade-60-100 gm/litre is used.

AlkaliAlkali is used for the following purpose- A. Alkali is used to maintain proper pH in dye bath & thus to

create alkaline condition. B. Alkali is used as a dye fixing agent. C. With out alkali no dyeing will take place. D. The strength of alkali used depend on the reactivity of dyes. E. As strong alkali caustic (NaOH) is used to create pH 12-

12.5 when the dye is of lower reactivity. F. As medium alkali sods ash(Na2co3) is used to create pH

11-12. when the dye is of medium reactivity.G. As weak alkali (NaHCO3) is used to create pH 10-11. when

the dye is of high reactivity.

Urea: Urea is used in continuous method of dyeing .It helps to get required shade of dye. To get dark shade more urea is used and for light shade less amount of urea used.

Soaping: By soaping the extra colour is removed from fibre surface thus Wash fastness is improved .Soaping increases the brightness and Stability of dye.

Chemistry of reactive dyes: Reactive dyes differ from other colouring matters in that they enter in to chemical reaction with fibre during dyeing & so become a part of fibre substances. A reactive dye is represented as R-B-X, where, RChromogen, B-Bridging group X-Reactive system. When it reacts with fibre, F, it forms R-B-X-F. Wet fastness of dyed material produced, depends on stability of true covalent bond X-F.

A. Dyes reacting through Neucleophilic substitution reactions

(1) Di-chloro-triazynilamino types of dyes:

These are more reactive than mono-chloro type of dyes & require lower temperature & milder alkali for dyeing & fixation. These are known as Cold reactive dyes brand.

(2) Mono-chloro triazynylamino type of dye:

These require higher temperature & stronger alkali for dyeing & fixation, are called hot brand reactive dye.

(3) Mono-fluoro-triazynylamino dyes:

(4) Bis–Triazinyl dyes. (5) Supra type of dyes. (6) Di or tri-chloro-pyrimidylamino dyes

B. Dyes reacting through Neucleophilic addition reactions:

(1) Dyes containing Vinyl sulphone group: As such this is not soluble in water, so it is marketed in its soluble form i.e., β-hydroxy ethylene sulphone sulphuric acid ester derivatives

RSO2 –CH2-CH2OSO3Na

(2) Dyes containing Acrylamido group: Carbonyl group is less powerfully electron withdrawing group & also reactivity is less as compared to vinyl sulphone type

(3) α- chloro acrylamido dye: Due to presence of chlorine atom, they are more reactive than acrylamido dyes.

Chemistry behind reactive dyeing:Dyeing principle is based on fibre reactivity & involves reaction of a functional group of dyestuff with a site on fibre to form a covalent link between dye molecule & substance. 4 structural feature of typical reactive dyes molecule are: 1. Chromophoric grouping, contributing colour 2. Reactive system, enabling dye to react with hydroxy group in cellulose. 3. A bridging group that links reactive system to chromophore, 4. One or more solubilising group, usually sulphuric acid substituent attached to chromophoric group for their colour, although Azo chromophore –N=N- is by itself the most important. All reactive dyes contain sodium sulphonate group for solubility & dissolve in water to give coloured sulphonate anions & sodium cations. Most reactive dyes have 1 to 4 of these sulphonate groups; General form of reactive dye is as follows:

S R----B----X • S = Water solubility group • R = Chromophore • X = Reactive System • B = Bond between reactive system & Chromophore

Reaction between cellulose & reactive dyes:

Dyeing of cellulosic fibers with reactive dyes consists of two phases: Firstly, exhaustion phase, where dye is absorbed by

material in neutral medium, Secondly fixation phases, where reaction between dye &

fibre takes place.

Control parameters of reactive dyeing:

Process parameters: Internal fabric pH Working liquor ratio on

the machine Effective salt

concentration (actual) Effective alkali

concentration (actual) Rate of heating Rate of cooling Fixation temperature

Raw materials: Man (training,

understanding, supervision) Water Common chemicals (Salt,

Alkali) Specialty chemicals

(Auxiliaries) Reactive dyestuffs

STAGE OF DYEING:

First stage (Dissolving of the dye): In this first stage, the dye, in solid form, is equilibrated according to the dye dissolved in molecular form or in micellar form (aggregates of many molecules with good solubility), or in form of dispersed micropowder (microcrystals of dye molecules poorly soluble)

Second stage (Adsorption): During this stage, by the effect of the dye-fibre affinity, the dye is adsorbed at the surface of the fibre, thus forming chemical bonds with it.

Affinity, temperature, (sometimes pH and/or auxiliaries) affect the thermodynamic interactions: a) The balance of the reactions, thus determining the exhaustion degree of the dyeing liquor. b) The affinity between the dye and the fibre is the ability of both dye and fibre to form a permanent bond. The greater the affinity, the stronger and higher are the fibre-dye bonds and the smaller is the dye for the solvent (water). Generally it is also directly proportional to the molecular weight (molecular size) of the dye. Affinity is therefore a condition strictly related to the chemical composition of the dye and the fibre

A quick adsorption of the dye on the surface of the fabric reduces the dye concentration near the fibre, thus reducing the adsorption speed. A correct speed of the liquor change in contact with the fibre allows the maximum concentration of the dyeing solution near the fibre, and consequently the correct speed. At the same time, the liquor flow in contact with the material is spread homogeneously and allows a good distribution of the dye in all the areas of the textile surface; this enhances the dye consistency with the same operating times. The adsorption reaction is usually sufficiently quick not to affect the dyeing speed, and often it must be slowed down or adjusted (T°, pH, and auxiliaries) on optimum values to avoid an irregular distribution of the dye.

Third stage (Diffusion): During this stage the dye, adsorbed in molecular form by the surface, by breaking and restoring the bonds many times tends to penetrate into the bulk of the fibre through amorphous areas, to spread homogeneously and fix steadily.Figure: Dye concentration in the liquor near

the fibre depending on the hydrokinetic condition

Fundamental factors are: Crystallinity of the fibre: the dyes penetrate the

fibers through amorphous areas and therefore the higher the crystallinity, the lower the diffusion speed.

Molecular size of the dye: the bigger the dimensions of the dye molecules, the more difficult the diffusion through amorphous areas.

Strength or dye-fibre bonds (affinity): the stronger the bond, the more difficult the diffusion.

Fibre makes the diffusion quicker but simultaneously reduces the affinity and therefore the exhaust. The presence of auxiliaries, facilitating the fibre swelling or increasing the concentration of dye near the fibre (swelling agents), tends to increase the diffusion speed. The operating time must be adequate to allow a good penetration of the dyes, since this is a prerequisite for developing the maximum fastness.

Hydrolysis of reactive dye:

Under alkaline reactive dye reacts with the terminal hydroxyl group of cellulose. But if the solution of the dye kept for long time its concentration drops. Then the dye react with the hydroxyl (OH) group of water. This reaction of dye with water is known as hydrolysis of reactive dye. After hydrolysis dye con not react with fiber. So hydrolysis increases the loss of dyes.

Hydrolysis of halogen containing reactive dyes: D-R-Cl + H-OH DR-OH + HCl

Hydrolysis of activated vinyl compound containing group: D-F-CH2-CH2-OSO3H + H-OH D-F-CH2-CH2- OH + H2SO4

Stripping of reactive dye Partial stripping: Partial stripping is obtained by treating the dyed

fabric with dilute acetic acid or formic acid. Here temperature is raised to 70-100 C and treatment is continued until the shade is removed by desired amount.

Acetic acid -------------- 0.5 - 10 g/L Temperature ----------- 70 – 100 C Full stripping: For complete stripping the goods are first treated with

sodium hydro sulphite (Hydrose) at boil and then washed off and bleached with 1 g/L sodium hypochlorite (NaCl) or bleaching powder at room temperature. This is carried out as following steps- Wetting agent ------ 0.5 – 1.0 g/L NaOH -----------------3-6 g/L       (Temp100-105 x 60-30min) Hydrose ---------------7-10g/L Then, Wetting agent --------------1g/L (Room Temp x 10min) Bleaching powder ---------1g/L

Influencing factors of dyeing: Salt. Soda. Time. Temperature. pH. Wetting agent. Sequestering agent. Anti-creasing agent Leveling agent All of these above are important in dyeing but we have

worked with time, temperature, and pH.

Effects of different parameters used in reactive dyeing:

Time: Time is very important in dyeing. The fixation of dye depends on time. With the increase of time the fixation of dye will increase. For example if a fabric is dyed in a dyeing bath for five minute the amount of dye it will absorb is less than the amount of dye will absorb by a same fabric in ten minute. As we have worked with reactive dye so the optimum time for fixation of this dye is sixty minute. If a fabric is dyed for sixty minute with reactive dyes it will show all required properties, i.e. wash fastness, rubbing fastness, light fastness, perspiration fastness etc. Temperature: Higher temperature causes the hydrolysis of the dye with water to become more frequent. Experiment showed that high temperature caused the cotton material to have a very poor ability to be dyed. Higher temperature cause cotton material to absorb dye more because of the molecules having more kinetic energy, thus more collision would occur between dye molecule and fibre, increasing the chance of a reaction taking place and bond formation.

pH: In the case of most popular fiber reactive dyes, a high pH actually activates the cellulose fiber, forming a cellulosate anion, which can then attack the dye molecule, leading to a reaction that produces a strong, permanent covalent bond. Without a high pH, the dye will not fix permanently to the cellulose fiber. Sodium carbonate is used for to increase the pH of the dye reaction, so that the fiber will react with the dye. Color:Color is the sensation which occurs when light enters the Eyes. It is rising from the activity of the retina of the eye and its attached nervous mechanisms. This activity is being, in nearly every case in the normal individual a specific response to radiant energy of certain wavelength and intensity. The hue refers to the actual color sensation (red, blue, yellow), the sensation or Chroma(depth of color) to the degree of differentiation from grey(dull of vivid), and lightness to the amount of light reflected from the object (light or dark). In the Munsell color system, these attributes are assigned alphabetic and numerical levels. Light: That aspect of radiant energy of which a human observer is aware through visual sensations arising from stimulation of the retina by the radiant energy. The wavelength of perceived colors of visible spectral light are between 380 to 740.

After treatment:

•In the dyeing of deep shades or inefficient washing equipment there may be incomplete removal of unfixed dye. •After treatment with cationic dye fixing agent. •Insolubilizes the unfixed dye. •Improves wash fastness. •Treated with 5-10 g/L cationic dye fixing agent at 50-60º C for 10-30 mints. •Treatment with dye fixing agent is not substitute of wash off process.