* The role of alkali in reactive dyeing

When dyeing with reactive dyestuffs, soda ash is often used as the alkali in dyestuff manufacturers' recipes. Recently, however, a synthetic alkali has appeared. What is the role of alkalis in reactive dyeing and what should be considered when choosing one?

In the dyeing of cellulose with reactive dyes, alkali is necessary because it acts as a catalyst in the reaction between the dyestuff and the fiber. The important point is not the type or amount of alkali but rather the pH of the dyebath, which must be closely supervised.
The most suitable pH for dyeing varies with the temperature, being approx. 11.5 for common warm dyeing (dyeing at approx. 60°C), 10-11 for hot dyeing (80°C) and 12.5 for cold dyeing (40°C). The relationship between temperature and the optimum pH is shown in the following graph.

Soda ash is often used because 20g/l usually produces a pH of around 11.5. However, it can be used with sodium phosphate or caustic soda when a higher pH is required, or with sodium bicarbonate (baking soda) when a lower pH is required. Caustic soda is not often used because it is a strong alkali and achieving a pH in the range of 10-12 is difficult. Nothing prevents it from being used, however, if the pH can be adjusted accurately with automatic equipment.
Recently introduced alkaline agents specifically for use with reactive dyes adjust the pH of the dyebath to a level suitable for dyeing with reactive dyestuffs and are easy to use because they come in liquid form, but the alkaline agent to be used should be chosen in consideration of the optimum pH for the temperature at which the dyestuff is to be used. The pH of the first bath is often checked to determine the pH for the dyeing, but attention should be paid to the pH after dyeing because if alkali is not added in sufficient quantity, the pH at the conclusion of dyeing may be considerably lower.

* How to wash printed Polyamide fabrics?

1. 2.0 g/L Setafix ANF (10 min. cold rinsing)
2. 1.0 g/L Setafix ANF (10 min. cold rinsing)
3. 10 min. cold rinsing
4. 1.0 g/L Setalan PM-8 at 30C, 10 min.
5. 1.0 g/L Setalan PM-8 at 40C, 10 min.
6. 1.0 g/L Setalan PM-8 at 40C, 10 min.
7. 2.0 g/L Setafix ANF at 50C, 20 min.
8. %2 Setafix ANF, pH:5.0 with Acetic Acid at 50C, 20 min.
9. Rinsing at 30C

Pre - treatment of Modal fabrics?

Viscose and Modal fibers are supplied in the pure state and with an incomparably higher degree of whiteness than cotton. Bleaching processes are, therefore, only required for completely white products (reduced quantities of chemicals) or pastel shades.
While tending to be unaffected by the usual chemical concentrations, viscose and Modal fibers react rapidly and intensely on coming into contact with alkali. Both fiber types are capable of being activated by a lye concentration of 4.5% (7°Bé) to such an extent that a distinctly higher dye absorption results.

While a concentration of 4.5% NaOH (7°Bé) represents the upper limit as far as viscose fibers are concerned, Modal fibers can, leaving aside the critical range of 7% to 15% NaOH, be treated with mercerizing lye of 17% to 22% (24–28°Bé). For bleaching products the temperature should not be allowed to exceed 180°C, e.g. heat-setting of blends with PES. Prior to thermal reaction, the fibers must be generally free of alkali residues.

Pre - treatment receipe for white products:

Setabicol BAC :6 g/L

Setalub ACA :1 g/L

Hydrojen Peroxide (50%) :4 g/L

Temperature : 90 - 98°C

Time : 45 - 60 min.


Note: Creases can occure if material is wet and wait. Centrifugal machine should not be used at any stage and it must be dried immediately after all wet processes.

* How to dye Black polyester at 98C?

% 0.20 Setapers Orange H-3R

% 6.00 Setapers Black CE-RN

3 g/L Setacarrier HT, dyeing at 98C for 60 min.

* How to strip Turquoise dyed cotton material?

15,00 g/L Hydrosulphate
6,00 - 7,00 g/L Caustic Soda
3 g/L Setalan IW

95C, 20 - 30 minutes.

Note: Please make a trial in laboratory before application in the bulk.

* What are Exhaustion curves of Setazol Yellow 3RS, Red 3BS and Blue BRF? What are important fastness properties of Setazol Blue BRF?

- Three dyes has very close Exhaustion curves and therfore this combination obtain level dyeing with good reproducability,

- Setazol Blue BRF has high light fastness in 1/1 depth is (6),

- Setazol Blue BRF has lower Chlorinated Water (3) and Gas fastnesses (3).

* If requirement for shrinkage of Viscose knitted fabric is less than 5%?

a) If requirement for shrinkage of Viscose knitted fabric is less than 5%, it should be used a Free Steam dryer instead of normal stenter. After free steam dryer, material should be sanforazed in a sanforization machine.

b) Material should be in the Process as following;

- Weak Cold Caustification (it can help for better size stabilisation and less creasing of the fabric)
- Dyeing,
- Open width free steam dryer,
- Sanforization.