Reactive dyeing and its working

 

Overview

Reactive dyeing is one of the most widely used and adaptable techniques in the textile industry, and it is a crucial step in the coloration of fabrics. Reactive dyes are renowned for their vivid hues, exceptional light and wash fastness, and capacity to create robust covalent connections with textiles. This blog explores the realm of reactive dyeing, including its types, benefits, history, chemistry, and environmental impact.

The Background of Reactive Dye

Imperial Chemical Industries (ICI) initially introduced reactive dyes in the 1950s. Prior to their creation, the most common dyes were sulphur, vat, and direct; however, their shade range and fastness qualities were limited. The advent of reactive dyes, which offer brilliant colours and superior fastness qualities, signalled a substantial breakthrough in textile dyeing technique.

Reactive Dye Chemistry

The color-imparting groups in reactive dyes are called chromophores, and they are joined to the fibre via covalent connections with reactive groups. Reactive groupings that are most prevalent include:

MCT, or Monochlorotriazine
DCT, or Dichlorotriazine
Sulphatoethylsulphone (SES)  

Vinyl Sulfone (VS)

Nucleophilic substitution or addition processes are usually involved in the reaction between the reactive dye and the fibre. The hydroxyl groups in cotton, the most widely dyed fibre, react with reactive dyes. The overall response can be shown as:

OH + Dye-R-X → OH + Dye-R-X + HX
Wool-OH+R-Dye-X→Fiber-O-R-Dye+HX

where X is a group that leaves during the reaction and is moved.

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Reactive Dye Types

Based on their reactive groups and dyeing behaviour, reactive dyes are categorised as follows:

Cold Brand Dyes: 

These dyes are appropriate for high reactivity and low substantivity because they react at lower temperatures (30–40°C).

Dyes for Medium Brands: 

These dyes react at temperatures between 40 and 60 degrees Celsius, providing a balance between substantivity and reactivity.

Hot Brand Dyes: 

These dyes have low reactivity but high substantivity, and they need to be fixed at temperatures between 60 and 90°C.

The Method of Reactive Dyeing

Several crucial phases are included in the reactive dyeing process to guarantee uniform dye uptake and fixing on the fibre:

Cloth Preparation: 

To ensure optimal dye absorption, the cloth needs to be thoroughly cleaned and bleached to eliminate any impurities.

Dyeing: 

An alkali, salt, and reactive dye are added to a dye bath in which the fabric is submerged. While alkali (sodium carbonate) aids in anchoring the dye to the fibre, salt (often sodium chloride or sodium sulphate) encourages the dye's exhaustion onto the fibre.

Rinsing and Washing: 

To get rid of any leftover colour, the fabric is completely rinsed after dying. In order to stop bleeding and enhance wash fastness, this is essential.

Soaping: 

To get rid of any hydrolyzed (unreacted) dye, the fabric is washed at a high temperature using a detergent. The dyed fabric's fastness qualities are improved by this procedure.

Variables Affecting Reactive Dyeing

The result of the reactive dyeing process is influenced by several factors:

• Temperature: 

In general, higher temperatures accelerate the dye-fiber reaction, but they can also accelerate the dye's hydrolysis.

• pH: 

Because it affects the dye's reactivity, the dye bath's pH is very important. The majority of reactive dyeing procedures operate in an alkaline pH range.

• Time: 

Enough time must pass for the dye to fully react with the fibre.

• Concentration of Alkali, Salt, and Dye: 

To guarantee optimal fixing and uniform dyeing, the concentrations must be adjusted.

Benefits of Dyeing Reactively

Compared to other dyeing techniques, reactive dyeing has the following benefits:

1. Reactive dyes yield vivid and bright hues.
2. Excellent wash and light fastness are the outcome of the covalent link between the dye and the fibre.
3. Cotton, wool, silk, and nylon are just a few of the fibres that reactive dyes can be applied to.
4. Reactive dyes come in a lot of varieties that are made with less energy and water in them.

Obstacles and the Effect on the Environment

Reactive dyeing offers numerous advantages, but it also presents certain difficulties:

• Water Use: 

The process of reactive dyeing uses a lot of water, particularly when rinsing and soaping.

• Management of Effluent: 

The dyeing process produces effluent that needs to be treated before being released because it contains dye, salt, and other chemicals.

• Energy Consumption: 

Heating is required for the dyeing and washing procedures, which adds to the energy use.

The industry is concentrating on sustainable techniques like these to address these issues:

• Low Water Dyeing Techniques: 

Supercritical CO2 dyeing and foam dyeing are two techniques that use less water.

• Effluent Treatment Plants (ETPs): 

Dye effluents are treated using sophisticated treatment technologies.

• Energy-Efficient Processes: 

Process optimisation and dyeing machinery innovations both contribute to lower energy usage.

Advancements in Reactive Dyeing Lately

Reactive dyeing technique has recently advanced with the goal of improving performance and sustainability:

• Biodegradable Reactive Dyes: 

These dyes have a smaller ecological impact because they decompose more readily in the environment.

• Reactive dye digital printing: 

This technique uses less water and chemicals by applying dyes precisely and waste-free.

• Reactive dyes that are low in salt or salt free reduce the amount of salt used, which helps to mitigate one of the main environmental issues with reactive dyeing.

Summary

Because reactive dyeing can produce vivid, long-lasting colours on a variety of fibres, it has completely changed the textile dying industry. Even though there are certain environmental drawbacks, more sustainable methods are becoming possible because to continuous study and technical developments. Reactive dyeing is a procedure that can be used by manufacturers to minimise their ecological effect while producing high-quality outcomes. Reactive dyeing is still a mainstay of textile colours, combining sustainability and performance as the industry innovates.