Sulpher dyes dye liquor preparation

  Dye liquor preparation of sulpher dye:

In sulpher dye molecules contain Sulpher linkage and to make it soluble in water needs to add a reducing agent Na2S. Due to the use of this chemical this dye is named sulpher dye. 

Na2S+ 4H2O →Na2so4 + 8H

Dye-S-S-Dye + 2H→Dye-SH+ SH-Dye 

This dye after being absorbed by textile fiber is insoluble again and is fixed with fiber. Due to this wet fastness is very good. The substantivity of sulpher dye is not so good. But if we use sodium salt or glubar salt then its substantivity is increased. After a certain stage, the dye exhaustion of dye liquor will not be the same. Then if we again use salt but it will not increase dye exhaustion. To increase dye exhaustion in the fiber we heat dye liquor. 

Dye solution making: First of all we need to take a pot and there need to take some hot water then add some Soda Ash. After that, we need to add Na2S as a reducing agent. Then we need to vibrate the mixture. After that again need to add some hot water to make the solution mix well. There must take a double quantity of Na2S of dyestuff. Sometimes need to use hot Na2S. When we add soda ash with dye solution then any kind of acid will be removed. If we do not get a clear solution then we can add some Na2S again. Sulpher yellow color produce needs to use Caustic soda to dissolve dyestuff. 

Application of sulpher dyes: In the maximum stage, during the use of Sulpher dye we need to boil the liquor. That temperature (60-100°C ) needs to continue the dyeing process for 30 minutes. After that dyeing steam stops and make the liquor is cold and processed for 30 minutes. There are some dyes that can perfectly dye fabric from 70°C to 75°C. 

Similarities of sulpher dye and direct dye:

1. We can dye cellulosic fiber with both types of dye. 

2. If we mix dye in base solution then they produce insoluble color. 

3. Both dyes can make a colloidal solution. 

4. To increase color fastness need to use metallic salt. 

5. Both dyes have good wet fastness. 

6. Both dyes have good light fastness. 

Dissimilarities of Sulpher dye and Direct dyes: 

1. Sulpher dyes are insoluble in water so we need to use Sodium sulfite but the direct dye is soluble in water. 

2. Sulpher dye can be decomposed by acid but direct dye never be decomposed. 

3. Sulpher dye can make Sulphuric acid with the contact of air but direct dye never makes it like that. 

4. Sulpher dye is mainly for black color but direct dye can be used for any type of color. 

5. Sulpher dye's wet fastness is very good but direct dyes' wet fastness is not so good. 

6. Need oxidation for color but direct dye has no need for oxidation.  

7. Protein fiber can never be dyed by sulpher dye but direct dye can be dye protein fiber. 

8. Sulpher dye contains sulpher group but direct dye contains sulphonic, benzene, and an amine group. 

9. This can get as powder and liquid but direct dye always is in powder form. 

10. Sulpher dye application process is complex but the direct dye application process is not complex.