pretreatment is the heart of wet processing.Presentation Transcript
Welcome To Our
• Our Presentation Topic Is pretreatment is
the heart of wet processing.
Md: Al Mottaki
Pretreatment is a heart of processing of textile.
In Pretreatment, all these impurities are
removed and fabric is brought to a stage where
it is more absorbent and white and can be
easily processed further.
The process which is done to make the textile
materials suitable for dyeing and printing. Such
as singeing, desizing, scouring, bleaching etc.
Flow chart of pre treatment of
All the processes of this stream are carried out in
an aqueous state or aqueous medium. The
main processes of this section include :
• The verb ‘singe’ literally means ‘to burn
superficially’. Technically, singeing refers to the
burning-off of. Loose fibers not firmly bound into
the yarn and/or fabric structure. Singeing is an
important part of pretreatment. This is the
burning off of protruding fiber ends from the
surface of the fabric.
• Singeing is the process is removing the hairs of
fabrics or fibers. In singeing process, we use
three technique to applied it. Such as, gas
flame technique. At the end of this process, we
will find, that the fabrics is smoother than before
and the fabrics wet ability is increase.
Technique of singeing:
Singeing Process is as follows:
• To produce a smooth surface finish on fabrics made from
staple fibers first the fabric surfaces are brushed lightly to
raise the unwanted fiber ends.
• Then the fabric is singed with or passed over heated
copper plates or open gas flames. The fiber ends burn
• The fabric is moved very rapidly, and only the fiber ends
• As soon as the fabric leaves the singeing area, it enters a
water bath or Desizing bath. This stops any singeing
afterglow or sparks that might damage the cloth.
Figure of singeing M/C:
• Desizing is the process or removing the starch
or size the covering the warp yarn
using enzyme. Oxidizing agent, or other
chemicals. There are three types of technique
in desizing and four method of desizing that
has been used.
Objectives Of Desizing:
• To eliminate the water repellent nature of sized cloth.
• To increase the absorbency.
• To reduce the consumption of chemicals in subsequent
Technique of desizing:
• Enzymatic Desizing.
• Oxidative Desizing.
• Acid Steeping/Desizing.
• Rot Steein.
• Desizing with hot caustic soda treatment.
• Hot washing with detergent.
• Removable of water soluble sizes.
• Atmospheric Plasma Desizing.
The hydrolysis of starch using enzymes under
particular concentration, temperature and
duration is called enzymatic desizing.
Enzymatic desizing is the most widely
experienced method to desize the starch.
Advantages & Disadvantages:
• No usage of aggressive chemicals: No
damage to the fiber.
• Wide variety of application processes.
• Lower additional cleaning effect towards other
• No effect on certain starches (e.g. tapioca
It is used to remove non-starch sizes that don’t
dissolve in water.
A variety of oxidants can be applied after
padding the hydrogen per oxide (H2O2) and
steam for 2 to 3 minutes.
The advantages of oxidative desizing are
supplementary cleaning effect, effectiveness for
tapioca starches but oxidizing agents may
damage to fibres.
• Cold solutions of dilute sulphuric acid
(H2SO4) or hydrochloric acid (HCl) are utilized
to degrade starch and other sizes.
• However this method has also
disadvantage of bad affecting the cellulosic
fiber in cotton fabrics.
Lye (Caustic Soda) Desizing:
• In this method fabric containing starch would be
expanded under the hot solution
of sodium hydroxide (caustic soda -NaOH).
• Caustic soda dissolves starch and form
layer, can be separated.
• Padding the fabric in alkali and stacked under
60 ~80 C for 6 to
12 hours, the desizing process can be finished.
• Scouring is the process by which all natural and
additive impurities such as oil, wax, fat, hand
dust etc. are removed to produce hydrophilic
and clean textile material. It is one of the vital
processes of wet processing.
Objects of Scouring:
To make the fabric highly hydrophilic.
To remove impurities such as oils, waxes, gum,
husks as nearly as possible.
To increase absorbency of fabric or textile
materials without physical and chemical
To produce a clean material by adding alkali.
To make the fabric ready for next process. To
remove non-cellulosic substance in case of
Scouring process depends on:
The type of Yarn.
The color of Yarn.
The cleanliness of Yarn.
The twist and count of the yarn.
The construction of the fabric.
The shade % and type of shade of finished
Chemicals used in scouring
Main chemicals Use
Caustic soda Neutralize acidic materials, saponify
glycerides (waxes and oil),solubilise
Surfactants Reduce surface tension & minimize
Detergents Emulsify oil, fats, waxes and remove oil-
Chelating agent Deactivate metal ions.
Sodium silicate Penetrate & break drown lignin's.
Soda ash Maintain pH.
Solvent Assist emulsification by dissolving oily
Form of Scouring:
• Yarn scouring:
Continuous sheet warp form.
• Fabric scouring:
Open width form :
• Pad batch
• Progressive jig
• Scouring methods of Cotton:
Generally, there are two principle methods of
Discontinuous (Kier boiling process or winch
Continuous (Scouring in J or L box)
• Main parts of kier boiler:
Mixing tank(liquor prepared according to recipe)
Multi tubular heat exchanger(heating the liquor)
Perforated false bottom
Circular tube(spray liquor on fabric)
• Process: The working process in J-box can be divided
into four units. There are
Pre – heater.
J – box.
• 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.
The aim of bleaching can be
described as following:
• Removal of colored impurities.
• Removal of the seed coats.
• Minimum tendering of fibre.
• Technically reliable & simple mode of
• Low chemical & energy consumption.
• Increasing the degree of whiteness.
• Bleaching Agent
A bleaching agent is a substance that can
whiten or decolorize other substances.
Bleaching agents essentially destroy
chromophores (thereby removing the color), via
the oxidation or reduction of these absorbing
groups. Thus, bleaches can be classified as
either oxidizing agents or reducing agents .
Type of Bleaching Agents:
Oxidative Bleaching Agents
Reductive Bleaching Agents
Enzymatic Bleaching Agents
Recipe for Bleaching:
SOAP (DTC) 2ml/kg
Reaction time 25min.
• Oxidative bleaching – the bleaching agent is a
chemical reagent which decomposes in alkali
solution and produce active oxygen.
• The active oxygen is in fact the intrinsic
bleaching agent as it will further destroy partly
or completely the coloring matter present in the
• Reductive bleaching – the bleaching agent will
destroy the coloring matter by reductive
reaction of SO2.
Auxiliaries used for bleaching:
• Mercerization is one of the most important
finishing processes of cotton with a strong
caustic alkaline solution in order to improve the
lustre, hand and other properties. It imports
gloss to the fiber, increases its hygroscopicity,
strength and improves its dye affinity.
Mercerizing improves the reactions with a
variety of chemicals and elongation of the fibres
and also improves the stability of form.
Mercerizing process consists in treatment of
cellulosic materials with concentrated solutions
of caustic soda at a temperature of 15 to 18°C.
Purpose of mercerizing:
1.To improve the lusture.
2.To improve the strength.
3. To improve the dye uptake and moisture
Effect of Mercerization:
Increase ability to absorb dye.
Improve reaction with a verity of chemicals.
Improve stability of form.
It has been shown that the increase in the luster occurs
because of an effect.
The cotton fiber do convoluted.
The cross-sectional shape changes.
Knitted fabric mercerizing m/c.
Woven fabric mercerizing m/c.
Automatic hank yarn mercerizing m/c.
Chainlesss-padless mercerizing range.
Clip mercerizing m/c.
Open width fabric mercerizing m/c with caustic
Factors of Mercerizing:
• In mercerizing followings are important: