Reasons for Why so Called Sulpher Dye | Popularity of Producing Black Shades 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
Vat Dye
Molecular Size
Dye molecules are very Large
Smaller than Sulpher
Shade
Gives dull shade due to varying conditions
Gives bright shades
After reduction
Smaller size molecules are obtained
D–S–S–D+[H]D–SH + SH–D
Vat dyes are reduced .
Fabric Dyed
Cotton, Rayon, Nylon & P/C
Cellulose Rayon etc
Hydrolysis
Under high temperature and Humidity
Susceptible to hydrolysis i.e. easy to Hydrolysis.
Wash Fastness
Good to very good
Excellent
Price
Cheaper than Vat dye
Very costly dye
Light fastness
Good to very good
Excellent for anthraquinone.
Sulpher linkage
Contain Sulpher linkage
No Sulpher linkage is present.
Ionization
The dye molecules are negatively ionized after reduction
Same
 

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