2. Properties of Sulphur Dye
• They contain sulphur linkages within their molecules
• Sulphur dyes are insoluble in water
• They are soluble in a solution of sodium sulphide (Na2S)
• The sodium sulphide (Na2S) acts as a reducing agent, severing
the sulphur linkage and breaking down the molecules into
simpler compounds, which are soluble in water
• The wash fastness is good and the light fastness is satisfactory
• Have poor fastness to chlorine
3. Mechanism of Sulphur Dyeing
• The insoluble dye is converted to smaller soluble components called
thiols by reducing agent
Dye.S – S.Dye + 2H Dye.SH + HS.Dye
(Insoluble (Reducing agent) (Thiols)
sulphur dye) Smaller components of dye
soluble in water
• The thiols containing the SH group are readily oxidised in the fibre to the
original insoluble sulphur dye, giving a colour with a very good washing
fastness
Dye.SH + HS.Dye + O Dye.S – S.Dye + H2O
5. Dyeing of Cellulose with Sulphur Dye
Dyestuff is pasted
with soda ash and
sodium sulphide
Boiling water is then
added to the paste
until the dye
dissolves
Dyebath is prepared
with the dye paste +
Sodium Chloride /
Glauber salt (Added
gradually at 1000C)
The fabric is
impregnated in the
dye bath and dyeing
is carried out at boil
for 60 minutes
The extra liquor is
squeezed off
immediately
The fabric is then
oxidized with a
solution of sodium
perborate at 40-500C
for 20 minutes
After oxidation, soaping is carried out at boil for 20 –
30 minutes followed by hot water and cold water
washing
6. After Treatment
• The washing and light fastness can be
improved by using one of the following after-
treatment
– Treatment with metallic salt e.g. dicromate and copper sulphate
either alone or in combination
– Topping with basic dye
• Cotton goods dyed with sulphur colour can be topped with basic
dyes so as to get enhance brilliance shade and improved washing
fastness properties as well
7. Disadvantages of Sulphur Dye
• The major disadvantages of suphur dyes are
– Bronziness of Shades
– Tendering of sulphur black dyed goods
• Bronziness of Shades
– Occur due to 1) presence of dyestuff on the material, because of dyeing in a strong
bath; 2) Use of excessive quantity of common salt during dyeing; 3) excessive delay
in washing after draining the dye liquor; 4) insufficient quantity of sodium sulphide
present during dyeing and resulting incomplete dissolution of dyestuff
• Tendering of sulphur black dyed goods
– Sulphur black dyed cotton goods degrade on prolong storage
– This is due to the formation of sulphuric acid (free sulphur on exposure to moisture
gets converted to sulphuric acid)
