Reactive dyes are a class of highly coloured organic substances, primarily used for tinting textiles, that attach themselves to their substrates by a chemical reaction that forms a covalent bond between the molecule of dye and that of the fibre. The dyestuff thus becomes a part of the fibre and is much less likely to be removed by washing than are dyestuffs that adhere by adsorption.
The first fibre reactive dyes were designed for cellulose fibres, and they are still used mostly in this way. There are also commercially available fibre reactive dyes for protein and polyamide fibres. In theory, fibre reactive dyes have been developed for other fibres, but these are not yet practical commercially. The dyes contain a reactive group that, when applied to a fibre in a weakly alkaline dyebath, form a chemical bond with the fibre. Reactive dyes can also be used to dye wool and nylon, in the latter case they are applied under weakly acidic conditions.
The most important characteristic of reactive dyes is the formation of covalent bonds with the substrate to be coloured, i.e. the dye forms a chemical bond with cellulose, which is the main component of cotton fibers.
Fiber reactive dyes are the most permanent of all dye types. Unlike other dyes, it actually forms a covalent bond with the cellulose or protein molecule. Once the bond is formed, what you have is one molecule, as the dye molecule has become an actual part of the cellulose fiber molecule. No wonder you can safely wash a garment that has been dyed in bright fiber reactive colours with white clothing, a hundred times, without endangering the whites in the least - even if it is all different bright colours, or even solid black! In contrast to all other dyes the reactive dyes bind chemically to the textile fibres, significantly improving the product's colour stability and washability. Thus reactive dying of cotton is currently the most widespread textile dying process in the world.
Properties of reactive dye
- During the dyeing process, the reactive group of the dye makes covalent bond with the fiber.
- These dyes are soluble in water.
- These dyes are normally used for dyeing cellulose and protein fibers.
- All types of shades are available from these dyes.
- The dyeing is done in alkali condition
- Wet fastness is well
- The brightness and rubbing fastness are comparatively well
- The cost of these dyes is cheap
- The dyeing process is very easy.
- This dye reactive group reacts with –OH groups of cellulose and –NH2 group of proteins fiber.
Reactive Dyes may be classified in various ways as below:
On the basis of reactive group:
a) Halogen (commonly chlorine) derivatives of nitrogen containing heterocycle, like 3 types-
- Triazine group
- Pyridimine group
- Quinoxaline dyes
b) Activated vinyl compound:
- Vinyl sulphone
- Vinyl acrylamide
- Vinyl sulphonamide.
On the basis of reactivity:
- Lower reactive dye: Here ph is maintained 12-12.5 by using NaOH in bath.
- Medium reactive dye: here pH is maintained 11-12 by using Na2CO3 in dye bath.
- Higher reactive dye: here pH is maintained 10-11 by using NaHCO3 in dye bath.
On the basis of dyeing temperature:
a) Cold brand:
These types of dyes contain reactive group of high reactivity. So dyeing can be done in lower temperature i.e. 320-600C.
b) Medium brand:
This type of dyes contains reactive groups of moderate reactivity. So dyeing is done in higher temperature than that of cold brand dyes i.e. in between 600-710C temperatures.
c) Hot brand:
This type of dye contains reactive groups of least reactivity. So high temperature is required for dyeing i.e. 720-930 C temperature is required for dyeing.
Production of Reactive Dyes in India
In India there are over 100 units engaged in making different types of reactive dyes both in the organized sector as well as small scale sector. Table 1 below gives the data of production of reactive dyes in the organized sector only.
Table 1: Production of Reactive Dyes in the Organised Sector In Tons
Source: Ministry of Chemicals & Petrochemicals
It is understood that the share of organized players is around 60% and that of ssi units at 40% in the total production. Thus, the total production of reactive dyes in India is estimated at 200,000-tons in 2017-18.
Kiri Industries Ltd., Meghamani Dyes, Bodal Chemicals, McFills Enterprises, Colourtex Industries, Jay Chemicals, Jaysynth Dyestuffs and kolorjet Chemicals are among some of the major players engaged in making reactive dyes in India. Most of these producers are located in Gujrat and Maharasthra.
Exports & Export Potential
Exports of reactive dyes from India have grown from 69,031-tons in 2010-11 to nearly 150,000-tons in 2017-18 (see Table 2 ). Details of exports to different destinations and top 8 importers from India are given in Tables 3 & Fig 2 respectively.
Table 2: Exports of Reactive Dyes Exports: Qty. in Tons; Val:in Rs. Lakhs
Share of different hues
Of the total reactive dyes exported Reactive blacks constitute 46%, followed by Reactive Blues 17%, Reactive Reds 16% and Yellows 13%.
Figure 1: Exports of Reactive Dyes by Colours
Table 3: Destinations of Exports of Reactive Dyes from India
Export Potential for Reactive Dyes
Table 4 provides the data on major reactive dyes buyers from the world. It can be seen from the table that while countries like Brazil, Singapore, Turkey and Bangladesh may appear to be saturated markets, countries like China, Indonesia, Thailand, Germany, Pakistan, Vietnam and Korea still offer enough scope for increasing exports to these regions.
Table 4: Major Reactive Dyes Buyers from the World
Source: UN Statistics