Reactive Dyes

What is reactive dyes?

Reactive dye is a dye that may create a covalent bond with a fiber, providing a long-lasting attachment that cannot be dissolved by repeated boiling water treatments under neutral conditions. As a result, the dyes are incorporated into the fiber, providing exceptional color fastness to washing. For a strong fabric bonding, reactive dyes make a covalent bond with a fabric molecule after coming into touch with it. Reactive dyes are frequently employed in the textile industry on a variety of fabrics, including cotton, wool, and silk. Reactive dyes are used for a variety of common purposes, including as inkjet printing, discharge printing, and exhaust dyeing.

Why reactive dye is so called?

Because this is the only type of dye containing a reactive group, which reacts chemically with fiber polymer molecules to form covalent bonds, reactive dyes get their name. The reactive group and the terminal -OH (hydroxyl) group of cellulosic fiber and wool fiber or the reactive group and the terminal -NH2 (amino) group of polyamide polymer produce this covalent link. This covalent bond has greater strength than ionic, hydrogen, and Vander Waal forces of attraction. Thus, the reactive group is incorporated into the fiber.

For this reasons the dyes are so called. They are also called ‘fibre reactive group’.

History of Reactive dye

 To commemorate the 100th anniversary of the creation of synthetic dyes, two ICI Company (UK) chemists named Stephen and Rattee attempted to create a brand-new dyestuff. Thus, they were able to create a brand-new dye in 1965 that they termed REACTIVE DYE. This product was created for cellulosic fabric coloring. The society of dyes and colorists awarded the first three reactive dyes, PROCION YELLOWR, PROCION BRILLIANT RED 2B, and PROCION BLUE 3G, a gold medal for their efforts in 1960.

Categories of Reactive Dyes

Generally, there are two categories:

  1. Nucleophilic substitution process is used by reactive dyes to react.

Cell–OH + HO ⇒ Cell–O + H2O

Cell–O+ Dye–Cl ⇒ Cell–O–Dye + Cl

  • Using a nucleophilic addition process, reactive dyes

Cell–O+ Dye–SO2–CH=CH2 ⇒ Dye–SO2–CH=CH2–O–Cell

The general structure of reactive dyes:

Fibers that can be successfully coloured with reactive dyes include:

  1. Other cellulosic fibers include flax, cotton, rayon, and rayon.
  2. Wool fibers and polyamide.
  3. Acetate and silk fibers.

It encompasses hues ranging from light to dark and spans a wide spectrum of colors, including,

Purple, Blue, Green, Red, Black, and Yellow ctc.

Classification of Reactive Dyes:

  1. According to Chemical Constitution:

Reactive dyes can be categorized into the following categories:

  • MCT Chlorotriazine Dyes
    • Vinyl Sulphone Dyes
    • Mixed Dyes (MCT-VS)
    • Containing Heterocyclic Helogens
  • Depending on the temperature application methods:

Reactive dyes can be categorized into the following groups according to application techniques and temperature:

Reactive dyes under the Cold brand: These dyes are applied at very low temperatures. The temperature ranges from 25 to 50 degrees Celsius. At this temperature, they are strongly reactive with fiber.

Reactive dyes of the medium brand are applied at temperatures between 40 and 60 degrees Celsius. Their reaction to fiber is moderate.

Low-brand reactive dyes: Compared to medium-brand dyes, these dyes have very low fiber reactivity qualities. Dyeing is carried out on 60 -90 degree Celsius.

Properties of Reactive dyes

Reactive dyes have the qualities listed below. These are

  1. First off, reactive dye is an anionic substance.
  2. Reactive dye is also a water-soluble dye.
  3. Additionally, they have superior wash and light fastness qualities.
  4. They therefore possess greater substantivity.
  5. As a result, they establish a powerful covalent link with the cellulose fiber.
  6. Additionally, dyeing must be done in an alkaline environment.
  7. Furthermore, electrolyte is essential for the fiber’s dyes to exhaust themselves.
  8. During application, a certain number of dyes are also hydrolyzed.
  9. Reactive dyes also enable the production of a wide range of colors.
  10. Lastly, it is reasonably priced.

Reactive dyes’ influencing variables:

Reactive dyes have an impact on cellulosic fiber dyeing in certain ways. During the dyeing process, the following elements should be taken into account.

  • Reactive dyeing is carried out in an alkaline environment; as a result, the pH of the dyeing bath should be controlled. The ideal pH range is 11.5 to 11.
  • Depending on the manufacturer of the reactive dyes, the temperature should stabilize
  • Electrolyte concentration: The type of shade affects the electrolyte concentration
  • Time: The recommended dyeing time is 60 to 90 minutes
  • Liquor ratio: A significant amount of water is used during the dyeing process. The efficiency of dyeing is improved by a higher liquor ratio.

The Dying Process of Reactive Dyes

When an electrolyte is present, dye exhaustion or absorption may occur.

Washing the unfixed dye from the material’s surface after fixation under the action of alkali

Advantage of Reactive Dyeing

  • Brilliant colors
  • Color permanence
  • Covalent fixation with a high Wash Fastness (WF)
  • Various temperatures, including low-energy (cold dyeing)

Disadvantage of reactive dyeing

  • Hydrolysis issues leading to incomplete fixing
  • Wash-off is necessary (for high WF)
  • High salt content is required
  • Processes used to treat wastewater cannot simply remove color, and in many situations, the dyes are not easily degradable.

Precautions of reactive dye

  • High reactive colors shouldn’t be dissolved in hot water since hydrolysis could occur
  • Due to dye hydrolysis, prepared dye solutions cannot be kept for later use
  • Low reactive dyes are used to create print paste
  • A protective mask is necessary since it is harmful to breathe in reactive dye particles
  • The majority of reactive dyes have a short storage life.

Conclusion

Reactive dyes have numerous uses in a variety of industries, to sum up. These dyes can carry out a variety of tasks in various chemical and physical settings and are very reactive and selective. Reactive dyes’ uses in more industries will expand as their qualities are more understood and developed in the future.

MD. Foysal Kazi

Department of Textile Engineering

BGMEA University Of Fashion & Technology (BUFT)

Campus Ambassador at Crystalline Textile Solution

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