Dyeing operation is performed by the reaction between fiber and dyes. Some dyes are water soluble and some are water insoluble. Some fiber has affinity to dye; some have no affinity to dyes. So dyeing depends on both fiber and dyes chemical properties. Before dyeing we have to consider this factor.
Reactive dyes are the most common and huge uses dyes all over the world. Most of the dyeing operation of natural fiber is done by reactive dyes. Reactive dyes have a worldwide acceptance to the dyeing technologist for dyeing cotton. This article is about reactive dyes.
Reactive dye is only class of dyes which makes co-valent bond with the fiber and becomes a part of it. This can be described as:
Reactive dyes + Fiber = Reactive dye-Fiber (Co-valent bonding)
If the general structure of a reactive dye is “R-B-X” then,
R-B-X + Fiber = R-B-X-Fiber (Dyed fiber)
R = Chromophore Group (Azo, Anthaquinone, Phthalocyanine, Metal complex group)
B = Bridging Group ( Imino, Ethyl & Methyl, Oxide, Sulphide group)
X = Reactive Group (-Cl, -Br, -SH, -OCH, etc)
Examples of reactive dyes:
Classification of Reactive Dyes:
- By depending on chemical constitution reactive dyes can be classified as:
- Chlorotriazine Dyes (MCT)
- Vinyl Sulphone Dyes (VS)
- Heterocyclic Helogen Containing Dyes (HHC)
- Mixed Dyes (MCT-VS)
- By depending on application methods of temperature, reactive dyes can be classified as:
I.Cold brand reactive dyes: This type of reactive dyes is applied in very low temperature. Temperature lies between 25 -50 degree Celsius. They are highly reactive with fiber on this temperature.
II.Medium brand reactive dyes: This type of dyes is applied in a medium temperature range is 40 – 60 degree Celsius. Their reactivity is medium with fiber.
III.Low brand reactive dyes: This type of dyes has very low reactivity properties with fiber with comparison with medium and high brand reactive dyes. Dyeing is carried out on 60 -90 degree Celsius.
Properties of reactive dyes:
- Reactive dye is anionic in nature.
- Reactive dye is a water soluble dye.
- They have better wash and light fastness properties.
- They have better substantivity.
- They form strong co-valent bond with the cellulosic fiber.
- Alkaline condition is must required for dyeing.
- Electrolyte is must for exhaustion of dyes in the fiber.
- A certain amount of dyes are hydrolyzed during application.
- Wide range of color can be produced with reactive dyes.
- Comparatively cheap in price.
Influencing factors: Dyeing of cellulosic fiber with reactive dyes is influenced by some factor. Following factors should consider during dyeing operation.
- pH: Reactive dyeing is done in an alkaline conditon for this reason pH of the dyeing bath should control. pH should be between 11.5 -11.
- Temperature: Temperature should fix depending on the brand of reactive dyes.
- Concentration of electrolyte: Concentration of electrolyte depends on the type of shade.
- Time: Dyeing time should be between 60 – 90 minutes.
- Liquor ratio: Huge amount of water is use during dyeing operation. Higher the liquor ratio betters the efficiency of dyeing.
Reactive dyes have some advantage and disadvantage to use. Different famous dyes manufacturing companies produce reactive dyes with different characteristics. So, select your ones depending on your demand.