Reactive dyes

Reactive Dyes

1. REACTIVE DYES DYEING OF CELLULOSIC MATERIAL

2. Properties of Reactive Dyes Readily soluble in water Presence of sulphonic group ( - SO 3 H) Unlike direct dye, reactive dye molecule tends to be much less substantive to cotton Requires large quantities of salt for exhaustion React and combine chemically with cellulose with co- valent bond Reactivity of the dyestuff can reduced by blocking one of the two reactive chlorine atoms 2

3. Properties of Reactive Dyes Reactive dyes are not so long as that of direct dyes Easy penetration Good levelling Good washing fastness Due to Covalent bonds Formation of covalent bond between dye and fibre occurs in alkaline condition Presence of acid reverse this process Perspiration is acidic, hence this fades the colour 3

4. Classification of Reactive Dyes Alkaline controllable dyes Salt controllable dyes Temperature controllable dyes 4

5. Alkali controllable dyes Low substantivity Require slow and progressive addition of alkali Encourage migration of dye to the substrate Prevent simultaneous exhaustion and fixation 5 Dye + Salt Alkali Exhaustion % Total dye exhausted on to the fibre Total dye fixed

6. Salt controllable Medium to high substantivity reactive dyes Need to control during the electrolyte addition stage i.e. portion wise addition of addition of salt is required Exhaustion % of this group of reactive dye due to salt is much higher than that due to the alkali 6 Dye + Salt Alkali Exhaustion % Total dye exhausted on to the fibre Total dye fixed

7. Temperature controllable dyes This dye react with cellulose above the boil in the absence of alkali They can be used as “Salt controllable dyes” with alkali fixation being done at 80 – 100 C These dyes are self levelling Control of rate of temperature gives good results 7

8. Classification depending upon the fibre – dye bond Tri- azinyl ring type These dyes react with cellulose by a process of substitution For example: Monochloro-triazinyl dye, Dichlorotriazinyl dye Vinyl sulphone dye These dyes react with cellulose by the mechanism of addition 8 D Cl R Mono-chlorotriazinyl dye D Cl Cl Di-chlorotriazinyl dye D – SO 2 – CH = CH 2

9. Classification based on Reactive system Monofunctional reactive dyes Bi-functional reactive dye Homo- bifunctional Hetero- bifunctional Multifunctional reactive dye 9

10. Mono functional reactive dyes Characterized by the presence of reactive groups (one or two reactive species) at individual locations in the dye molecule All reactive dyes developed during the early stages of development were monofunctional reactive dyes Ex: Dyes having either monochloro or di-chloro triazine or vinyl sulphone reactive groups Although di-chlorotriazine contains two reactive Cl atoms, located at the same triazine ring they are considered as mono functional reactive dyes 10

11. Bi-functional reactive dyes These dyes are induced recently to the reactive dye range Characterized by the presence of two reactive groups of same type or two different type at two different locations in the dye molecule Homo functional – Dye molecule contain two reactive systems of same type Hetero functional – Dye molecule contain two reactive systems of mixed type 11

12. Examples MCT / MCT Monocholorotriazine / Monocholorotriazine VS / VS Vinyl sulphone / Vinyl sulphone MCT / VS Monochlorotriazine / Vinyl sulphone FT / VS Fluro triazine / vinyl sulphone 12

13. Speciality of Bifunctional reactive dyes These dyes have high exhaustion leading to high fixation and better colour yield Due to high exhaustion the quantity of dye in the dye bath and that removed during washing is small High fixation is due to Presence of two reactive groups 13

14. Dyeing of Cotton with Reactive Dyes Involves the following steps Dyeing in the presence of NaCl for better exhaustion Chemically reacting the dye and the fibre in the presence of alkali After treatment of the reactive cotton material (Soaping, washing etc.) Dyeing with COLD Brand Reactive dye Start at 30 C and maintain the temperature through out Add dye solution and add salt gradually for 30 minutes About 15 minutes after final salt addition add 1/10 th soda ash gradually After further 10 mintues add the remaining soda ash and continue dyeing for 30 – 45 minutes followed by drain, rinse and soap rinse 14

15. Dyeing of Cotton with Reactive Dyes Dyeing with HOT Brand Reactive dye Start at 50 C and add dye solution During next 40 minutes add salt gradually Start raising temperature while adding the 2 nd portion of the salt Raise the temperature to 80 C in 30 minutes About 15 minutes after the salt addition, add soda ash gradually for 15 minutes and continue dyeing for 30 – 60 minutes Followed by draining, rinsing and soap rinse 15