This document discusses the scouring and bleaching processes for various natural and man-made fibers. It explains that wool requires a mild scouring process due to its sensitivity to alkali. Scouring of wool uses sodium carbonate or ammonium carbonate at below boiling temperatures. Bleaching can be done with reducing agents like sodium bisulfite or hydrogen peroxide, which produces a permanent whiteness. For silk, degumming using hot soap solution is required to remove the sericin gum. Hydrogen peroxide bleaching is preferred for silk. Man-made fibers require milder scouring, and polyester rarely needs bleaching, while nylon and acrylic can be bleached using sodium chlor

1. SCOURING & BLEACHING
WOOL

2. SCOURING
Scouring of wool differs from cotton in the following respects
 Raw wool contains anything from 30% to 60% of wool
grease, compared with 0.5% of oil and wax in cotton
 Wool is very rapidly degraded by alkali
So the alkali that must be applied should be mild and at
temperature well below boiling
Sodium hydroxide is never used
Mild alkali like sodium carbonate or ammonium carbonate
or ammonia is used

3. • Raw wool is scoured by counter – current method
• The machine contains generally four to five bowls containing scouring
liquor and water
• The wool fibres are moved continuously from the 1st bowl to the last bowl
• Scouring is done in the 1st three bowls and washing is done in the 4th bowl
• Soap and alkali are added in the 1st component and detergent in the 2nd
and 3rd bowls

4. Soap (%) in solution Alkali (Sodium
carbonate %)
Temperature (0C)
First Bowl 0.8 0.2 50
Second Bowl 0.4 - 45-48
Third Bowl 0.37 - 42-45
Fourth Bowl Water only - 40
The pH should never be allowed to rise above 10 and the temperature not above
600C

5. BLEACHING
• Bleaching using reducing agents
– The bleaching action of reducing agents used for bleaching is due to
the action of bi-sulphite ions (HSO3
-)
– In practice wool can be bleached either exposing the wool to
• Sodium bi-sulphite (NaHSO3) , or
• Sulphur dioxide (SO2)
• The use of reducing agents used for bleaching wool is limited
– The whiteness is not permanent due to aerial oxidation

6.  Bleaching wool with hydrogen peroxide
 The whiteness produced by hydrogen peroxide is permanent
 The pH and temperature is to be controlled, otherwise degradation of
wool fibre will take place
 The pH is kept between 8 – 8.5 and the temperature should not exceed
600C
A mixture of sodium hydroxide and sodium carbonate is
used to maintain the pH
 Wool hydrogen peroxide bleaching also requires stabilizer to control the
decomposition of peroxide. Sodium silicate is used as stabilizer

7. Method of Bleaching wool
Preparation of bath
in stainless steel
with 2 volume sol. of
H2O2 + 0.5% sodium
silicate at 500C
The scoured
material is entered
in the bath and
worked out for 20 –
30 minutes
Cooling the bath for
3 – 4 hours
Material is taken out
and rinsed in water
Soured with dilute
acetic acid
Rinsing with water

8. Degumming & Bleaching
SILK

9. • Raw silk is composed of ‘fibroins’ connected with a gum like protein
known as ‘sericin’
• The presence of sericin gives the silk a harsh feeling
• Therefore, the sericin is to be removed from raw silk to increase the lustre
and softness of the silk filaments
• Again, since the silk filament contain some natural colouring material,
hence, it requires removal to get white silk filaments

10. DEGUMMING
• Silk gum or sericin is removed
• The process is commonly known as “boiling off’ or
‘degumming’
• Degumming is done by using hot soap solution (mild alkali can
also be used)
• Degumming is carried out by treating the silk for 2 hours, or
more if necessary at 950C with liquor ratio of 1:30

11.  The solubility of sericin depends upon the alkalinity produced by hydrolysis
 Silk can also be degummed with a mixture of sodium carbonate and
sodium bi-carbonate at pH 10 (this process however is not so efficient as
soap)
Recipe:
Soap solution – 0.5% to 0.75%
Temperature – 950C
Time – 2 hours
M:L ratio – 1:30
** It is to be noted that during degumming, vigorous mechanical stresses
are to be avoided or else rupture of fibroin filament will take place

12. Bleaching
• Oxidative or reductive bleaching can be used for silk
• Bleaching generally follows the degumming
• For a full-white optical whiteners can be added to the subsequent
reducing bleach bath after oxidative pre-bleaching
• Hydrogen peroxide bleaching is most preferable

13. SCOURING & BLEACHING
MANMADE FIBRES

14. SCOURING
• Manmade fibres are comparatively free from impurities
• So, milder methods of scouring is sufficient
Rayon
• Scouring is done at 70 – 900C
• Scoured with soap and detergent
Recipe: Soda ash: 1 – 2 g/L
Detergent: 1 – 2 g/L
Temperature: 700C
Time: 30 min

15. Cellulose Acetate
• Chance of hydrolysis if the temperature is too high and if the scouring
liquor is more alkaline
• Only soap is used for scouring (slightly alkaline)
Recipe: Detergent: 1 g/L
Temperature 800C
Time 30 min
Polyester
• Same recipe as that of rayon

16. BLEACHING
• Polyester
– Normally bleaching is not required for the man-made fibres
– Bleaching is done in exceptional cases
– Best bleaching agent is NaClO2
Recipe: Sodium chlorite 1 – 5 g/L
Sodium nitrate 1 – 3 g/L
Formic acid 1 – 2 g/L
Temp At boil (≈ 1000C)
Time 60 – 90 min

17. Polyamide (Nylon) bleaching
• Nylon fabric is rarely bleached
• If at all bleaching is required, a mild sodium chlorite plus formic
acid/acetic acid (for pH 4) bleaching treatment is given at 700C
Recipe: Sodium chlorite 1 g/L
acetic acid / formic acid 2 g/L
Temperature Boil
Time 30 minutes

18. Acrylic Bleaching
• Does not require bleaching normally
• For extra white, it requires bleaching
• Sodium chlorite is used
Recipe: Sodium chlorite 2 – 3 g/L
Sodium nitrate 2 – 5 g/L
pH (Formic acid) 4
Temperature 850C
Time 30 – 45 minutes