Reactive dyes was introduced in 1956, primarily belongs to a class of highly colored organic substances. While dyeing the reactive groups of reactive dyes forms covalent bond between fibre polymer and dye which makes dye integral part of fibre. Hence, they are known for its enhanced fastness property. These dyes have stable electron arrangement which protect fibre from the adverse effect of ultra-violet rays. The significant chemical bonding improves the overall color stability and washability of the product makes these dyes most permanent of all other dye types. Undoubtedly, it is one of the most popular dyes used in textile industry all across the world.
Types of Reactive Dyes
Vinyl Sulfone Dyes commonly known as ‘VS dyes’ are moderately reactive. VS dyes use the mixture of caustic soda and soda ash and dyed at the temperature of 60 degree and 11.5 pH level. They show excellent fixation properties under alkaline conditions.
Bi-functional Dye is another form of Reactive dyes that multiple reactive groups in the molecular structure. They are designed to exhibit the capacity to react with fibre in more than single way.
Monochlorotriazine Dye, known as ‘MCT dyes’ are less reactive than VS dyes. Typically, dyeing process of MCT dyes is carried out 80 degree C with 10.5 pH level to give proper fixation on cellulose fibres.
- Are found in powder, liquid and print paste form that support water solubility
- Improved wash fastness with rating about 4-6
- Better light fastness with rating about 6
- Good perspiration fastness with rating 4-5
- Moderate rubbing fastness
- Protect fibre from degrading effect of ultra-violet ray
- Give brighter shades which increase the appeal of the product
- Simplified dyeing method with no oxidation/reduction
- Dying process requires less time and low temperature
- Fibres dyed with reactive dyes can be safely washed even with white garments without the fear of losing its color
- Incomplete fixation with hydrolysis
- Need for wash-off (for high WF)
- Require high concentrations of salt which affect natural balance of watercourses
- High pH
- Few “AOX” dyes can be potentially harmful to the environment
Mechanism of Reactive Dye Fixation
Mechanism and molecular structure of Reactive dyes gave them capacity to be more stable and prominent dyes. The bonding utilizes dichlorotriazine as reactive linker, Nucleophilic aromatic substitution which allowed use of wide variety of chromophores.
Reactive dyes are cationic dyes, widely used for dyeing cellulose, protein and polyamide fibres. In past days, cellulose fibres were dyed with Direct or Vat dyes. However, later with the introduction of reactive dyes Direct and Vat dyes were substituted with Reactive dyes.
The advantages of Reactive dyes over Direct Dyes are as follows:
- Ability to procedure bright shades of wide range
- High levelling quality
- Good washing fastness
- Good light fastness
The advantages of Reactive dyes over Vat Dyes are as follows:
- One stage simple dyeing method
- Low temperature dyeing at less than 1000C
- Less expensive
Reactive dyes even substituted Metalized Azo dyes with more fastness and bright shade dyeing capacity.
Besides, clothes, reactive dyes are also used in paints, plastics, food, etc.