sulphur dyes

A brief presentation about sulphur dyes, used in textile dyeing

1. sulphur dyes
prepared by: Karamat ali saif

2. Sulphur dyes
Sulphur dyes are so called because sulphur
dyes contain disulphide ( S-S) linkage in their
chemical structure.
Sulphur black is the most important class of
sulphur dyes
Commercially successful black sulphur was first
prepared in 1893.
Applicable to cellulosic materials, not to wool
and protein fibers due to strong alkaline
condition.

3. Chemical structure
•The exact chemical structure of sulphur dye is
not known

4. characteristics of sulphur dyes
These are water insoluble dyes and have no
affinity for the cellulosic fibers
Have to be converted into water soluble
substantive form (leuco form) before application
to the textile materials.
This conversion is carried out by a treatment
with a reducing agent like dilute aqueous Na2S.
Dye.S-S.dye + 2H→ Dye.SH+SH.Dye
This leuco form is substantive to cellulosic
materials.

5. characteristics of sulphur dyes
They are absorbed on the fiber surface
Then they are reconverted original water
insoluble form of dye by oxidation
Oxidation is carried out by “airing” or by using an
oxidizing agent like sodium dichromate
( Na2Cr2O7).
Dye.SH+dye.SH → dye.S-S.dye + H2O
 gives best result when they are used to
produced black, black and brown shades but red
shades cant be obtained by sulphur dyes.

6. General properties
Contain sulphur linkages within their molecules.
Highly colored water insoluble dyes
Some dyes are partially soluble in water.
Good light fastness
Excellent wash fastness
This good wash fastness is due to larger
molecular size and insolubility in water.

7. Classification of sulphur dyes
•May be classified in may ways .
•But according to their solubality there are
essentially three classes.
1. Conventional or water insoluble dyes :
which have no substantivity to cellulosics
2. leuco sulphur dyes : which are water soluble
and non substantive to cellulosics
3. solubilised sulphur dyes : which are
substantive to cellulosics

8. Steps in dyeing
Dissolving the Dyestuff
 reduction: conversion of insoluble form to its
soluble form
 dyeing: dyeing of cotton with its solubalised
leuco form
 oxidation: reconversion of soluble sulphur dye
inside the fiber to its original insoluble form.
 soaping

9. Common Problems and Corrective
Actions
1. Poor Washing and Rubbing Fastness

poor washing and rubbing fastness is caused by
improper color dissolution, color precipitation,
poor solubality of dyes, insufficient washing after
dyeing etc.

10. Corrective actions
•The dye dissolution must be complete
•It should be filtered befored adding to the dye
bath.
•Becouse insoluble dye particles if present will
cause unlevel dyeing and poor wash and rub
fastness.
•The color should be dissolved in sufficient
quantity of water, by keeping in mind the
maximum solubality of dye.

11. Corrective actions
•The water and salt should be free from calcium
and magnesium, which if present make insoluble
inert salt.
•The washing after dyeing and soaping must be
efficient to clear all the unused chemicals and
insoluble dye particles

12. 2. Bronziness
 Sulphur black has tendency to show bronze
appearance ( dull shades)
There are several reasons of bronziness
Insufficient quantity of sodium sulphide or reducing
agent resulting into quick oxidation of surface dyeing.
High concentration of common salt for exhaustion
Delay between dropping of bath and washing.

13. Corrective actions
Proper dissolution of dye stuff
Using sufficient and calculated quantity of
reducing agent
Using appropriate quantity of common salt
After treatment in bath containing Na2S solution
(1-2 g/l) at room temperature
After treatment in a liquor containing soap and
olive oil ( 1-2 g/l ) at temperature 60 c for 30
minutes.
Drying without rinsing.

14. 3. Tendering
Tendering means the loss of strength or degradation
of cellulosic materials upon storage.
Tendering is caused by the acid formation from the
free sulphur present in the dyed materials by the
action of moisture and air.
The acid produced reacts with cellulose and degrade
it, resulting in loss of strength

15. Corrective actions
The tendering can be minimized by giving after
treatment with acid neutralizing agent
Treatment of dyed fabric with sodium acetate
Drying without rinsing
Presence of sodium acetate on dyed fabric
converts harmful sulphuric acid to harmless
acetic acid

16. THE END
THaNk
you