Application of Reactive dyes to other fibres
(1) Reactive dyes on wool -
Reactive dyes contain acid groups and so they behave as anionic dyes under acidic conditions.
When the salt linkages are formed the reaction between the chlorine atom within the acid group of the dye and also the amino groups within the wool ends up in the formation of covalent bonds with the result that the dye molecule is extremely strongly attached to the fibre.
Satisfactory results, however, are not obtained by the application of the cold dyeing technique with the di chloro triazine dyes because when the scales structure remains intact penetration is just too slow at low temperatures unless assisted by an Organic solvent which adds significantly to the dyeing cost.
At higher temperatures near the boiling point, penetration is satisfactory.
Adsorption as has been explained earlier precedes fixation by covalent bonds. In most cases, this involves comparatively low pH values. Below pH 5 However, there's a significant increase in the rate of hydrolysis of the dye with the result that the proportion which becomes fixation on the fibre decreases.
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| Reactive dyes on wool |
The rate of fixation of the mono chloro triazine is incredibly much slower. The result's that there's abundant opportunity for the traditional acid dyeing mechanism to grant uniform distribution of the dye molecules before they become permanently anchored by bond formation.
It has been found that cationic surface-active compounds tend to skitter. To prevent foaming the addition of a silicon antifoaming product is usually recommended
The method of application is to form the dye bath at 40°C with ammonium acetate to provide a pH of seven for pale shades.
The material is run within the liquor for fifteen minutes after which the pH is tested and adjusted if necessary.
Running of the machine is then continued for one more quarter-hour so that uniformity of pH may be achieved.
After this, the cationic and nonionic assistants are added after an interval of 5 minutes the temperature is raised to a boil at which it's maintained for one hour
The reactive dyes give very bright shades on wool with a light fastness of the order 5 to 7 and wash fastness of 4 to 5.
(2) Dyeing of silk/wool blends -
The dye is of the same class for both types of fibre, although silk exhibits a higher initial strike rate at low temperatures, and migrates to wool at higher degrees.
There are two ways of dyeing these blends -
(1) Dyeing in the neutral region
(2) Dyeing in the weakly Acidic region
Explanation-
(i) Dyeing in the neutral pH region-
As illustrated in the figure below, dyeing in the neutral zone at 90°C with a large amount of electrolyte, such as 20 to 60 GPL Glauber's salt, and then chilling to 40°C is followed by an alkali fixation phase using sodium bicarbonate or soda ash in the same bath.
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| Neutral dyeing at 90°C |
(ii) Dyeing within the weakly Acidic region-
At pH 4.5 to 5.5 with ethanoic acid and sodium acetate and a little amount of electrolyte at 70°C followed by an Alkaline fixing introduce the identical bath with hydrogen carbonate or soda and 20 to 60 GPL Glaubers salt as shown in the figure below.
(Reactive dyes on Silk and nylon with their application)
Questions -
- Describe the application of reactive dyes on wool fibres.
- Describe applications of reactive dyes on silk-blend fibres.
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
(N.d.). Textilelearner.net. from https://textilelearner.net/reactive-dyes-classification-dyeing-mechanism/
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/
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)
