Characteristic, Properties and Nature of Reactive Dyes

Nature of reactive dyes:  

The molecular structure of reactive dyes are smaller than those of direct dyes, and their smaller size is accompanied by a correspondingly lower substantivity. The molecules of  direct dyes are made deliberately large so as to build up the physical attraction between fibre and dye, thus making them more substantive. Smaller molecules may be suitable for use as reactive dyes because one covalent bond between textile fibres and reactive group of reactive dye is about thirty times as strong as one Vander Waals bond between fibre and dye. As the size of a dye molecule becomes larger the colour it imparts becomes duller. Reactive dye molecules therefore confer very bright colours to dyeings because their molecules need be no larger than those of simple acid dyes.

Properties of Reactive dye:

1. During the dyeing process the reactive group of the dye forms covalent bond with the fibre. 
2. Solubility in water of those dyes are very effective.
3. Reactive dyes are normally used for dyeing cellulose(usually cotton fibre) and protein(usually wool) fibre. 
4. All types of shades are available from reactive dyes. 
5. The dyeing is done in alkaline condition. 
6. Wet fastness of finished textile materials are well. 
7. The brightness and rubbing fastness are comparatively well. 
8. The costs of  reactive dyes are cheap. The dyeing process is very easy. 

Comparison among  properties of major types of Reactive dye:

Reactive Group	Commercial name	Reactivity	Exhaust Dyeing Temp(°C)
Dichlorotriazine (DCT)	Procion MX (Zeneca)	High	2 5 - 40
Monochlorotriazine (MCT)	Procion H (Zeneca)  Procion EXL(Zeneca) Basilen (BASF) Cibacron E (Ciba)	Low	8 0 - 85
Monofluorotriazine (MFT)	Cibacron F (Ciba)	Moderate	40 - 60
Difluorochloropyrimidine (DFCP)	Drimarene K (Clariant) LevafixE-A(Dystar) Levafix P-A(Dystar)	Moderate to low	3 0 - 50
Dichloroquinoxaline (DCQ)	LevafixE (Bayer/ Dystar)	Low	5 0 - 70
Vinyl sulphone (VS)	Remazol (Dystar)	Moderate	4 0 - 60
Trichloropyrimidine	DrimareneX (Clariant) Cibacron T (Ciba)	Low	8 0 - 95
Nicotinyltriazine (NT)	Kayacelon React (NipponKayaku)	Moderate to high	100-130

Characteristic structural feature of reactive dyes:

The simplest way of representing the reactive dyes follows:
S       C       B         X
Where,

S is the solubilising group
C is the chromophoric group
B is the bridging group
X is the halogen containing reactive group

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