Reactive dyes
- 3. Contents Introduction History Chemical Structure General Properties Classification of reactive dyes Dyeing Mechanism Advantages Faults and their remedies
- 4. Introduction Reactive dyes are a class of highly coloured organic substances, that attach themselves to their substrates by a chemical reaction that forms a covalent bond between the molecule of dye and that of the fibre. Reactive dyes are called so because this is the only type of dye that has a reactive group which reacts chemically with fibre part and form a covalent bond.
- 5. History of Reactive Dyes Reactive dyes first appeared commercially in 1956, after their invention in 1954 by Rattee and Stephens at the Imperial Chemical Industries Dyestuffs Division site in Blackley, Manchester, United Kingdom. They were awarded gold medal from the society of dyes and colorists for the year 1960.
- 6. General Structure of Reactive Dyes The general formula is R-B-X, where R=Chromophore group B = Bridging group X= Reactive group
- 7. Structure of reactive dyes The three characteristic features of a typical reactive dyes are: The chromophoric grouping, contributing the color and much of the substantivity for cellulose; The reactive system, enabling the dye to react with the hydroxy group with water and cellulose; chromophore; A bridge group that links the reactive system to the chromophore.
- 8. Properties Of Reactive Dyes Anionic dye Water soluble Easy to apply Need alkaline conditions Light fastness and wash fastness are high Wide range of shades Cheap Form strong covalent bond with cellulosic fibre Found in powder , liquid and print paste form.
- 9. Types Of Reactive Dyes On the basis of reactivity Lower reactive dye: Here pH is maintained 12-12.5 by using NaOH in the dye bath. Medium reactive dye: Here pH is maintained 11-12 by using Na2CO3 in the dye bath Higher reactive dye: Here pH is maintained 10-11 by using NaHCO3 in the dye bath.
- 10. On the basis of dyeing temperature: Cold Brand These types of dyes contain reactive group of high reactivity. So dyeing can be done at lower temperature.i.e 32 to 60C . For example : PROCION , M LIVAFIX Hot Brand This type of group contains reactive groups of least reactivity. So high temperature is required for dyeing.i.e 720 to 930 C . For example : PRICION H, CIBACRON
- 11. Steps Of Reactive Dyeing Exhaustion Fixation Washing-off
- 12. Step#1: Exhaustion Dye is absorbed by material in neutral medium. The required amount of dissolved dye is added to the dyebath at ambient temperature and circulated through the goods. The temperature is gradually raised to the recommended dyeing and fixation temperature and the required amount of salt is added in portions, to exhaust the bath.
- 13. Step#2 : Fixation The required (or recommended) amount of alkali is added to the goods with good circulation, and fixation (reaction) proceeds. The hydroxide ion, being a very small ion, enters the cellulose readily and the equilibrium reaction, the ionization of cellulose, is quickly established. Cell-OH + OH Cell-O + H2O
- 14. Exhaustion and fixation vs. time for two reactive dyes
- 15. Step#3 : Washing-off To achieve the high wet-fastness expected from a fiber reactive dyeing, all the hydrolyzed, unfixed dye has to be removed. A batch washing-off sequence might include: a cold water wash at 25 to 60 degC (75 to 140F); a hot water wash at approximately 60 to 80 degC (140 to 175F); scouring with anionic surfactant at 80 to 90 degC (175 to 200F); and all this followed by hot and then cold water washing.
- 16. Influencing Factors pH : Reactive dyeing is done in alkaline conditions for this pH of the dye bath should be between 11- 11.5. Temperature: Temperature should be fixed depending on the brand of dye. Time: Dyeing time should be between 60-90 minutes. Liquor ratio: Huge amount of water is used during dyeing operation. Higher the liquor ratio better the efficiency of dyeing.
- 17. Assistants used for dyeing with reactive dyes Salts : It neutralizes the reactivity of fibre surface when immersed in the solution. It puts extra energy to push the dye inside the fibre polymer i.e. increase absorption of dye. Alkali : To maintain proper pH of in dye bath and thus to create alkaline conditions. Alkali is used as a dye fixing agent.
- 18. Urea : It helps to get required shade of dye. Soaping: Extra color is removed from the fibre surface. .It increases the brightness and stability of the dye.
- 19. ADVANTAGES OF REACTIVE DYES Permanency of colour : Fibre reactive dyes can be easily said to be the most permanent of all dye types. This is because of an unique quality, like other dies it can be actuallyform a covalent bond with substrate (cellulose or protein Molecule) after the formation of bond, there is only are molecule as the molecule as the molecule of cellulose fibre molecule. Easy washing : The fibre that are dyed reactive dyes can be safely dyed even with white garments without danger of colouring it.
- 20. Chemical Bonding : Chemical bonds as explained above significantly improv es products colour, stability and wash ability. Thus no doubt reactive dye of cotton is presently most popular textile dyeing process in the word.
- 21. Defect : Bleeding in colors during washing, abrasion Remedy : Boil the fabric with caustic soda , treat the fabric with hydrogen peroxide (5 to 10 gpl , 60 t0 70 deg C ) to make the color fast. Defect : The fabric has been dyed in darker shade , uneven dyeing Remedy : To take out the color from fabric treat it wit caustic for 45 to 60 min at 70 deg C . Thereafter treat the fabric with 10 to 20 gpl Acetic acid for 40 to 60 min at 80-85 deg C. Faults and their remedies
- 22. Defect : Color staining in fabrics of darker shade Remedy: Dye the fabric in sulphur black . Defect : Uneven dyeing , marks of water , marks of colors Remedy : Wash the fabric with soap and re-dye in darker shade.
- 23. Conclusion Reactive Dyeing is truly an important dyeing phenomenon for cellulose materials. Among different classes of dyes for cellulosic fibres the reactive dyes are the only one that can attach themselves to the fibres by the covalent bond. Reactive dyes are coloured compound which contain one or two groups capable of forming covalent bond between a carbon atom or phosphorous atom of the dye ion or molecule and an oxygen atom, nitrogen or sulphur atom of a hydroxyl, an amino or a mercapto group respectively. The purpose of the present investigation is to obtain reactive dyes with a higher degree of reactivity.