For education purpose. Shyamol Textile Engineering college

1. Shyamoli Textile Engineering College
(A constituent college of the University Of Dhaka)
Submitted By: Submitted To:
Name: Ishtiaq Ahmed Engr. Md. Almamun Rony
ID : 82/18 Lecturer,
Department Of Apparel Manufacturing
STEC, DHAKA

3. Presentation on
Bleaching

4. Contents
eaching

5. Introduction
Bleaching is chemical treatment employed
for the removal of natural coloring matter
from the substrate. The source of natural
color is organic compounds with conjugated
double bonds , by doing chemical bleaching
the discoloration takes place by the breaking
the chromophore, most likely destroying the
one or more double bonds with in this
conjugated system. The material appears
whiter after the bleaching.

6. Mechanism of bleaching

7. Objectives

8. Factorsof
bleaching
process
usedfor
bleaching
agent
Many technical factors govern the selection of
one bleaching agent over another-
-generic type of fiber (cellulosic, wool, synthetic)
-physical from of fiber (yarn, woven or knitted fabric)
-product and process costs
-stability, and therefore reliability
-versatility of process (batch wise or continuous)
-degree of whiteness obtained
-extent of any fiber damage

9. Factorsof
bleaching
process
Auxiliaries
usedfor
bleaching
agent
• Anti-corrosion agents
• Sequestering agents (to removes ion from
a solution system by forming a ring which
does not have the chemical reactions of
the ion which is removed. It can be a
complexing or a chelating agent) .
• Wetting agents/detergents.
• Activators .
• Stabilizers.

10. Factorsof
bleaching
process
Auxiliariesused
forbleaching
Bleaching
agent
A bleaching agent is a substance that can whiten or
decolorize other substances. Bleaching agents
essentially destroy chromospheres (thereby removing
the color), via the oxidation or reduction of these
absorbing groups.
Types of bleaching agent
1.Oxidative Bleaching Agents
2.Reductive Bleaching Agents
3.Enzymatic Bleaching Agents

11. Sodium hypochlorite (NaOCl) Bleaching
• Sodium hypochlorite is the strongest oxidative bleach - used in textile
processing.
• NaOCl is a highly unstable compound at normal conditions of
temperature and pH . It doesn’t exist as solid form.
• Prior to bleaching with hypochlorite, it is necessary to thoroughly
scour fabrics to remove fats, waxes and pectin impurities. These
impurities will deplete the available hypochlorite, reducing its
effectiveness for whitening fabric.
• Product strength of hypochlorites is generally expressed as the
available chlorine content.

12. Application
1.Hypochlorite is used mainly to bleach cellulosic fabric.
2.It cannot be used on wool, polyamides (nylon), acrylics. These fibers
will yellow from the formation of chloramides .
3.Bleaching with hypochlorite is performed in batch equipment. It is not
used in continuous operations because chlorine is liberated into the
atmosphere.

13. Bleaching with Hydrogen Peroxide (H2O2)
• H2O2 was discovered in 1818.
• By 1940, about 65% and to-day about 90 - 95 % of all cotton and
cotton/synthetic blends are bleached with H2O2.
• It is available commercially as 35, 50 and 70 % solutions.
• It is a corrosive, oxidizing agent which may cause combustion when
allowed to dry out on oxidizable organic matter.
• H2O2 is an irritant to the skin and mucous membranes and dangerous
to the eyes.
• H2O2 - Ecologically acceptable

14. Uses
• H2O2 is the bleach most widely used for cellulosic fibers [cotton, flax,
linen, jute etc.) and well as wool, silk, nylon and acrylics.
• Unlike hypochlorites, peroxide bleaching does not require a full scour.
• Residual fats, oils, waxes and pectines do not reduce the bleaching
effectiveness of H2O2….Impurities help in stabilization.

15. Advantages
Rayon,
uipment.
ng and
oxide
or souring
ore absorbent
ds.

16. Methods of bleaching
1. Batch methods
*lime lined kiers
*jigger
*winches
2. Semi continuous
*Pad-roll
3. Continuous
*Vaporloc machine
*J-box

17. J –box Process
Machine Description:
1.Impregnation bath: Padded with caustic
soda/Peroxide and wetting agent at 70-80⁰ C for 30-
40 sec.
2.Pre Heater :Thermostatically control
system for 30 sec at temp 90-100⁰ C .
3.J-box : Fabric is stored for 1-2 hours at 98-
102⁰ C.NaOH/H2O2 solution reacts with impurities
and dissolves them.
4.Washing Unit: Fabric firstly hot wash and
then cold wash.

18. Kier boiler process
1.Filled with solution about ½ or 1/3
of the kier.
2. Filled fabric about 80-85%.
Steam is passed through the whole
kier.
3. Remove the pocket air otherwise it
will damage the cellulose structure.
3. After 1-2 hours kier is closed for 6
hours then scouring or bleaching will
be completed.

19. Points To Be Considered Before Bleaching
The points that are considered are given below –
· In case of proteinous fibers reducing type of bleaching agent is
used.
· If proper bleaching is not done, it will not give proper result.
· Jute, Hemp, Flax type fibers required two types of bleaching
chemicals, Firstly, oxidative is used and finally the reducing type agent
is used.
· Most of the bleaching's are performed in the presence of ideal
bleaching agent. H2O2 may be termed as ideal bleaching agent because,
it is very cheap. It has no side effect.

20. Reference
# http://textilelearner.blogspot.com/
# http://www.digilibraries.com/
# Encyclopaedia britannica 11th edition Chemical Technology in the
Pre-Treatment Processes of Textiles By S.R. Karmakar
# Textile Preparation and Dyeing By A K Roy Choudhury
# Textile Chemicals: Environmental Data and Facts By Katia Lacasse,
Werner Baumann
# Textile fiber to fabric by Bernard P. Corbman
http://www.slideshare.net/
# http://www.ptj.com.pk/