Introduction of Reactive dyes
- A dye, which is capable of reacting chemically with a substrate to create a covalent dye substrate linkage, is understood as a reactive dye.
- Nowadays reactive dyes are widely utilized in dyeing cotton materials.
- It reacts with fibre in presence of alkali and adheres as part of the fibre.
- Here the dye contains a reactive group and this reactive group makes a bond with the fibre polymer and acts as an integral part of the fibre.
- This chemical bond is created between the dye molecules and therefore the terminal –OH (hydroxyl) group of cellulosic fibres between the dye molecules and therefore the terminal –NH2 (amino) group of polyamide or wool fibres.
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| Reactive dyes |
- Stephen and rattee two textile chemists were the primary ones to indicate that certain dyes can chemically react with cotton fibre forming covalent bonds and thus becoming a part of the fibre itself.
- Before the advent of those Reactive dyes, it had been insufferable to realize good fastness to hot wet treatments in Cellulose dyed material, except within the vat class of dyes.
- Another unique feature of those dyes is the versatility of the applying procedure allowing them to be applied at temperatures starting from ambient dyeing of vat and sulphur dyes.
- Since reactive dyes don't have a high degree of in-built insolubility or level of Substantivity as high as direct dyes, dyes of small molecular size can be made. This allows levelling and dyeing to require place very rapidly compared with conventional dyes.
- Since their introduction in the 1950s reactive dyes have shown rapid growth; even today developments are happening.
- The combination of brightness, fastness and easy application related to reactive dyes enables this category of dyes to be the key class of dyes used today to paint cellulosic fibres.
The structure of a reactive dye is shown below-
Where,
D - Dye
The above dye is a triazine reactive dye in which the chlorine atom is the reactive site.
Properties of Reactive dyes -
(1) The reactive dyes are readily soluble in water.
(2) Unlike direct dyes the reactive dye molecules tend to be much less substantive than cotton and need much larger quantities of Salt for exhaustion.
I.e. - Salt required for reactive dye is over salt required for substantive dye because of the substantivity of Direct.
Dyes are more than reactive dyes.
Substantivity: Direct dyes > Reactive dyes
Salt required: Direct dyes < Reactive dyes
(3) These dyes unlike the other class of dyestuff react and mix chemically (covalent)with cellulosic.
It is this characteristic that offers them the name reactive dyes.
During dyeing, the reactive group of this dye forms a bond with fibre polymer and becomes an integral part of the fibre.
(4) Reactive dyes are cationic dyes, which are used for dyeing cellulose, protein and polyamide fibres.
(5) Reactive dyes are found in powder, liquid and print paste form.
(6) They have excellent light fastness with a rating of about 6.
(7) The dyes have a very stable electron arrangement and might protect against the degrading effect of ultraviolet rays.
(8) Textile materials dyed with reactive dyes have excellent wash fastness.
(9) Reactive dye gives brighter shades and has moderate rubbing fastness.
(10) Dyeing method of reactive dyes is straightforward. It requires less time and temperature for dyeing.
(11) Reactive dyes are comparatively cheap.
(12) Reactive dyes have good perspiration fastness with a rating of 4-5.
(13) Reactive dyes have good perspiration fastness.
(14) The reactivity of the dyestuffs is often reduced when desirable by blocking one among the reactive chlorine atoms giving the new brand form of reactive dye
(a) Clarity and brightness of the hue
(b) Easy penetration and thus good levelling
(16) Textile materials Colored with reactive dyes should be thoroughly rinsed and soaped. Reactive dyes can react with the hydroxyl groups of the water molecule to provide dye molecules with poor substantivity for the fibre.
It's these molecules which need to be removed by the washing-off process involving Soaping at the boil and rinsing. If these hydrolysed dyes don't seem to be removed poor rubbing fastness will result.
(17) The formation of the chemical bond between the dye and fibre occurs under alkaline conditions The presence of acid may reverse this process.
Perspiration and atmospheric pollution which are both slightly Acidic may affect textile materials Colored with reactive dyes and ends up fading.
(18) Reactive dyes are often applied to cellulosic fibres by exhaust dyeing (batch dyeing), semi-continuous dyeing (pad-batch) and continuous dyeing technique.
(19) After dyeing material is going to be washed off.
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| Reactive dyes and their properties |
Questions -
- What is reactive dye and how its applied to fabric?
- Which properties of reactive dye are useful?
References
Ahmed, S. (2014, September 29). Reactive dyes - classification. TextileTuts. https://textiletuts.com/reactive-dyes/
Chakraborty, J. N. (2010). Waste-water problem in textile industry. In Fundamentals and Practices in Colouration of Textiles (pp. 381–408). Elsevier.
Clark, M. (2011). Handbook of textile and industrial dyeing: Principles, processes and types of dyes (Matthew Clark, Ed.). Woodhead Publishing.
No title. (n.d.). Acs.org. from https://cen.acs.org/articles/96/i29/new-textile-dyeing-methods-make.html
Patwary, E. M. Z. (2012, February 18). Reactive dyes. Textile Fashion Study; Engr. Mohammad Zillane Patwary. https://textilefashionstudy.com/reactive-dyes-definition-classification-properties-and-influencing-factors/
Sayed, A. (n.d.). Why reactive dye is so called? Blogspot.com. from https://textileapex.blogspot.com/2013/11/reactive-dye.html
What are Reactive Dyes? Types of Reactive Dyes. (n.d.). Meghmaniglobal.com. from https://www.meghmaniglobal.com/what-are-reactive-dyes-types-of-reactive-dyes/
(N.d.). Textilelearner.net. from https://textilelearner.net/reactive-dyes-classification-dyeing-mechanism/
Continue reading,
Part 2 Classification of Reactive dyes
Part 3 The reaction of MCT and DCT of reactive dyes
Part 4 General Factors affecting the results of reactive dyeing
Part 5 Reactive dyeing method - DCT
Part 6 Bifunctional systems of reactive dyes
Part 7 Development of reactive dyes
Part 8 Reactive dyes on Silk and nylon with their application
Part 9 Industrial applications of reactive dyes
Part 10 After treatment of reactive dyes
Writer - Rushikesh Patil (Textile Engineer)
