Reasons for Why so Called Sulpher Dye | Popularity of Producing BlackShades with Sulpher Dyes | Comparison Between Sulpher Dyes & Vat Dyes

Reasons for why so called:

The dyes are so called as they contain Sulpher linkage within their molecules but dissolved in a solution of sulphide which acts as a reducing agent, breaking the Sulpher linkage and converting the molecules into simpler components which are soluble in water and substantive towards cellulose. 

Dye–S–S–Dye (Water insoluble Sulpher dye molecule)

Popularity of Producing Black Shades with Sulpher Dyes:

1. Low cost
2. Fair to good light fastness
3. High Wash fastness
4. Easy to apply
5. Low energy required
6. Chemical resistance is moderate to good.
7. Wide range of shades especially on heavy, durable shades on apparel fabric.

 Comparison between Sulpher & Vat Dyes:

 

Subject	Sulpher Dye	Vat Dye
1.   Molecular Size	1.      Dye molecules are very Large	1.   Smaller than Sulpher
2.   Shade	2.      Gives dull shade due to varying conditions	2.   Gives bright shades
3.   After reduction	3.      Smaller size molecules are obtained D–S–S–D+[H]  à D–SH + SH–D	3.   Vat dyes are reduced .
4.   Fabric Dyed	4.      Cotton, Rayon, Nylon & P/C	4.   Cellulose Rayon etc
5.   Hydrolysis	5.      Under high temperature and Humidity	5.   Susceptible to hydrolysis i.e. easy to Hydrolysis.
6.   Wash Fastness	6.      Good to very good	6.   Excellent
7.   Price	7.      Cheaper than Vat dye	7.   Very costly dye
8.   Light fastness	8.      Good to very good	8.   Excellent for anthraquinone.
10.             Sulpher linkage	9.      Contain Sulpher linkage	9.   No Sulpher linkage is present.
10.             Ionization	10. The dye molecules are negatively ionized after reduction	10.             Same