Reactive dyes readily dissolve in water and form covalent bonds with cellulose fibers, providing good washing fastness. They are classified based on their reactivity - alkaline controllable dyes require gradual alkali addition, salt controllable dyes require portion-wise salt addition, and temperature controllable dyes react above boiling temperatures. Bifunctional reactive dyes contain two reactive groups, allowing for high exhaustion and fixation during dyeing of cotton which involves dyeing with salt, forming covalent bonds with alkali, and post-treatment processes like soaping and washing.

1. REACTIVE DYES
DYEING OF CELLULOSIC MATERIAL

2. Properties of Reactive Dyes
• Readily soluble in water
– Presence of sulphonic group ( - SO3H)
– 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
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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
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4. Classification of Reactive Dyes
• Alkaline controllable dyes
• Salt controllable dyes
• Temperature controllable dyes
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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
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Dye + Salt Alkali
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
6Dye + Salt Alkali
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 – 1000 C
• These dyes are self levelling
• Control of rate of temperature gives good results
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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
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D
Cl
R
Mono-chlorotriazinyl dye
D
Cl
Cl
Di-chlorotriazinyl dye
D – SO2 – CH = CH2

9. Classification based on Reactive system
• Monofunctional reactive dyes
• Bi-functional reactive dye
– Homo-bifunctional
– Hetero-bifunctional
• Multifunctional reactive dye
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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
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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
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12. Examples
• MCT / MCT
– Monocholorotriazine / Monocholorotriazine
• VS / VS
– Vinyl sulphone / Vinyl sulphone
• MCT / VS
– Monochlorotriazine / Vinyl sulphone
• FT / VS
– Fluro triazine / vinyl sulphone
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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
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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 300C 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
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15. Dyeing of Cotton with Reactive Dyes
• Dyeing with HOT Brand Reactive dye
– Start at 500C and add dye solution
– During next 40 minutes add salt gradually
– Start raising temperature while adding the 2nd portion of the salt
– Raise the temperature to 800C 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
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