Reactive Dye

Reactive Dye

History: 
An announcement of great technical and commercial importance appeared in the journal of the society of dyers and colorists (1956, p55) under the column “Manufacturers Publications & Pattern cards” This concerned a circular on procion dyes (ICI) deseribing Procion Yellow R, Procion Brilliont Red 2B and Procion lue 3G all belonging to a new eloss (called reactive) of dyes, since the fixation to the fibre is achieved by direct chemical linkage. 

Introduction (Detonation):

Reactive dyes are water soluble dyes containing sulphonic acid groups and reactive groups like dichloride or monochloro tniazinyl groups or sulplato ethyl sulphone groups (from which vinyl sulphone reactive groups are formed during dyeing in the presence of an alkali)

The reaction of these dyes with the functional groups of the fibre is brought about by alkali such as sodicens carbonate, hydroxide, silicate etc. Reactive dyes from covalent bond with the fibre and becomes a part of the fibre. This type of dye has some reactive group which can react with –OH group of ccllulose and –NH2 group of proteins fibres. Due to this fact, these dyes are known as reactive dyes.

Classification of reactive dye:

A) Reactive dyes can be classified chemically into two groups:
 

i) Halogenated hetero cycles Eg> Tri chloro Triazine Tetrachloropyrinmidine.

ii) Activated vinyl compounds: Eg>D-So2-CH=CH2, vinyl sulphone is another commercially successful reactive group used in the manufacture of reactive dyes, Remeizol dyes belongs to this group.These dyes are marketed as sulphate ethyle sulphone dyes and may be repesented by D-S-G-X where u is –CH2-CH2-OSO3Na G is So2, S is the solubilizing group and D is the chromogenic part.

B) On the basis of reactivity reactive dyes can be divided into three groups:-

i) High reactive dye: This type of reactive dyes contains two chlorine atoms and portion-M dyed of dyes fall under this group. In dyeing with this class of dyes weak alkali like NaHCO3 is used.

ii) Moderate reactive dyes: Dyeing with this type of dye medium alkali (Na2co3) is used lavafix E falls under this class.

iii) Low reactive dye: strong alkali (NaOH) is used in this types of dyes. This type of dyes contain on chlorine atoms.

Chemistry:

For a long time chemists have been sacking a method of joining the dye molecule to the cellulose with covalent bond. At about the end of the 1940 decade workers turned their attention to the properties of dyes containing cyanotic chloride

i) residues or, in other words.
Triazinyl dyes is possible to make the chlorine atoms in cyanotic chloride combine with one, two or three compounds containing hydroxyl or amino groups attached to colored dye molecules.

The reaction with water, alcohols and amines are summarized be low-

NaSo3-DYE-NH- + HO cellulose

O
- Cellulose

NaSo3-DYE-NH- + Hel

And this can go to a stage further, although it does not in all cases do so at 200c to link with two cellulose molecules, as in

- Cellulose
NaSo3-DYE-NH-

- Cellulose
The triazinyl dyes can, at the same time undergo hydrolysis with water to form the compound represented by

NaSo3-DYE-NH- + 2H20

NaSo3-DYE-NH- + 2Hcl


Properties of reactive dye:
i. During the dyeing process the reactive group of the dye makes covalent bond with the fibre.
 
ii. These dyes are soluble in water.
 
iii. These dyes are normally used for dyeing cellulose and protein fibers.
 
iv. All types of shades are available from these dyes.
 
v. The dyeing is done in alkali condition
 
vi. Wet fastness is well
 
vii. The brightness and rubbing fastness are comparatively well
 
viii. The cost of these dyes are cheap
 
ix. The dyeing process is very easy.
 
x. This dye reactive group react with –OH groups of cellulose and –NH2 group of proteins fibre.

DYEING PROCESS

Standard salt-at-start technique:

Procion H-E and H-EXL Dyes As stated previously, an application process for garments dyeing must be short be simple ad have the potential to be automated. The standard recommendation for application of procion H-E and H-EXL dyes is the salt-at-start process. By adding the salt to the rotary-drum machine through the loading dour before filling with water, the need for lengthily addition via add tanks is avoided. This advantage, together with the possibility of hydro-extraction, can lead to processing times some two hours shorter than those of conventional piece-dyeing.

Problems of dyes and dyes process:

It cannot be said that dyeing with reactive dyes gives excessive leveling problems. Since the dyes have a low affinity. However, it can happen that it is necessary to discharge a dyeing. Which can be more or less difficult depending on the situation of the dye in relation to the fiber Thus in the case of cellulose fibre dye discharging before alkalinization of dye bath doesnot present any difficulty? Since hot washing with a detergent will extract the main part of the dye deposited in the fibre as it has a low affinity.

When instead the dye has already been covalently fixed to the fibre it is more difficult to eliminate as it is necessary to destroy the molecule chemically by means of oxidizer and/ or reduction process.
There are different reduction processes according to whether it is cellulosic or wool fibre in the first ease it is carried out in an alkaline solution in the second in acid.
Reducing disoharge on cotton:

Sodium hydrosulphite – 5 g/c
Caustic soda at 360c- 15m/l
Or calcinated sodium carbonate-15g/l
The process takes place for 60min at 60-900c

On wool:

Sodium hydrosulphite – 2-5% according to depth
Formic acid at 85%-1.3%

The process is started at 50-600C the temperature is raised to 980c and held for 20¢ then the goods are rinsed in hydrogen peroxide before re-dyeing.
In some eases the discharges is not complotted in a single treatment and so it is best in use a combination of oxidizer and reduction methods.