02 - Process sequence of wet processing.pdf

PROCESS SEQUENCES OF CHEMICAL
PROCESSING
Grey fabric Inspection &
Stitching
Shearing &
Cropping
Singeing
Desizing
Scouring
Bleaching
Drying
Mercerising
Dyeing Printing
Soaping & Drying
Finishing
Folding & Packing

Preparation / Pretreatment
Processes used to remove impurities from fibres
to make it dye able or printable.
Natural fibers and synthetic fibers contain
primary impurities that are contained naturally,
and secondary impurities that are added during
spinning, knitting and weaving processes.
Textile pretreatment is the series of cleaning
operations .All impurities which causes adverse
effect during dyeing and printing is removed in
pretreatment process.

Objective of Pretreatment:
To Convert fabric from hydrophobic to
hydrophilic state.
To remove dust, dirt etc from the
fabric.
To achieve the degree of desire
whiteness.

4
Preparation
Following are the steps to be taken
before going wet processing :
Grey inspection
Stitching
Shearing and cropping
Singeing

Desizing
Scouring
Bleaching
Mercerization
Typically a woven
cotton fabric would be
prepared by sequence
of process as shown.
In case of knitting
sizing step is not
involved
Preparation/Pretreatment
Singeing

SHEARING & CROPPING
In shearing ,the fibres are cut in an angular manner
on the surface of the fabric itself, resulting in a soft
feel
Singeing and shearing are almost the same in effect.
In singeing the fibres in the interlacement of the
fabric are burnt by flames whereas in shearing the
fibres are cut in an angular manner on the surface of
the fabric itself, resulting in a soft feel.

Singeing
Burning of protruding fibres from the surface of
fabric or yarn - A mechanical process
singeing refers to the burning-off of Loose fibres
not firmly bound into the yarn and/or fabric
structure.
Textiles materials are most commonly singed in
woven or knitted fabric form or in yarn form.
Makes fabrics smooth
Prevents pilling
Improves luster

Advantages of Singeing
Singeing of a fabric is done in order to obtain a
clean fabric surface which allows the structure of
the fabric to be clearly seen.
Fabrics, which have been singed, soil less easily
than un-singed fabrics.
The risk of pilling, especially with synthetics and
their blends, is reduced in case of singed fabrics.
randomly protruding fibres are removed in
singeing which could cause diffused reflection of
light.

Necessity of Singeing in Textile
Cotton materials are valued for their smooth appearance. After
the formation of fabric it has a fuzzy or hairy appearance due to
projecting fibers, thus affecting the luster and smoothness
Unsigned fabrics are soiled easily
The protruding fibers obstruct the subsequent dyeing and printing
process
Goods which are to be mercerized are signed to maximize the
luster
In fabrics of polyester and cellulosic fiber blends singeing is the
best method to control pilling, sometimes double singeing is done
to minimize the pilling.

Singeing Process
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 off.
The fabric is moved very rapidly, and only the fiber ends
are destroyed.
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.

02 - Process sequence of wet processing.pdf

Bio polishing
It is an enzyme treatment designed to
improve fabric quality and provide
following advantages:
Improve pilling resistance
A clear, lint and fuzz-free surface structure
Improved drape and softness
The effect are durable

Process
Cellulase enzyme is used
Enzyme dosage 1-2% owf
pH 4.5-5.5
Temperature 40-55o
C
Time 30-60 min.
It is similar to singeing as it also provide
similar effect on the fabric.

Fig. 7. Carbomatic®
Singeing Line by
Bejimac
Fig. 8. DORNIER
singeing machine for
circular knitted fabrics

What should control during
singeing operation?
Intensity and uniformity of flame
Working speed of the fabric to be singed
Effectiveness of singeing : should not add
harshness in the fabric
Should not damage the synthetic filament
yarn in the fabric

Sizing /Slashing
Slashing is the process where
Size is applied to warp yarns for
weaving.
The purpose of size is to protect
the yarn from the abrasive action
of the loom.
The process is carried out on a
Slasher and the application
procedure is called Sizing or
Slashing.

NATURAL SIZING AGENTS
Natural sizing agents are based on natural
substances and their derivatives:
Starch and starch derivatives; native starch,
degradation starch and chemical modified starch
products
Cellulosic derivatives; carboxymethlycellulose
(CMC),
methylcellulose and oxyethlycellulose

SYNTHETIC SIZING AGENTS
Polyacrylates
Modified polyesters
Polyvinyl alcohols(PVA)

DESIZING
Desizing is the process of removing the
size material from the warp yarns in
woven fabrics.
Sizing agents are selected on the basis
of type of fabric,

Desizing Starch
Once a starch solution dries, the
resulting film will not readily re dissolve
in water; therefore, to completely
remove starch from a fabric, the
polymer must be chemically degraded
to make it water soluble.
Three chemical methods can be used to
degrade starch into water soluble
compounds namely, Enzymes, Acid
Hydrolysis and Oxidation.

Major Desizing Processes
Rot steeping
Enzymatic desizing
Oxidative desizing
Acid steepimg

Rot steeping
Fabric is stored in warm water at 40-60o
C
overnight
It remove the starch and water soluble
impurities with natural reaction
Drawback:
Time consuming
One can not certain that in the given
duration size will remove completely

Oxidative steeping:
Starch and other added impurities are hydrolysed
through oxidation process followed by washing process.
Oxidizing agents:
Sodium Hypochlorite: 2.0-5.0 gm/lit. at room
temperature at pH 7.0
Hydrogen peroxide:3.0-6.0 gm/lit of H2O2 and 7.0-15.0
gm/lit Sodium Hydroxide, 40oC for 12-16 hours
Drawback:
Time consuming Process
Some time bleaching effect also obtain(If not require in
the end product)
chemical reaction where water is mostly used to break down the chemical bonds that
exists between a particular substance

Acid steeping
Acid hydrolysis lowers the molecular weight and
reduce starch to glucose.
Fabric is treated with Sulphuric Acid (0.5% to 1.0 %)
at 40o
C
It also remove the starch and water soluble impurities
with natural reaction
Drawback:
Tendering of cellulosic fibre if precautions are not
taken
If the acid remain in the fabric, whole lot may get
seriously damage or tendered

Oxidative Desizing of strach
The oxidative desizing methods are relatively
unimportant and when using them, damage to
fiber can never be completely avoided.

Enzymatic Desizing
Enzyme solution in water with 0.5% to
2.0% on weight of fabric enzyme
Require quantity of Common salt is also
required
Neutral pH
Other method fabric is run continuously
in machine having enzyme solution.
enhance the temperature stability of enzymes

ENZYME
Enzymes are high molecular weight protein
biocatalyst that are very specific in their action.
Enzymes are named after the compound they
break down, for example:
Amylase breaks down amylose and amylopectin,
Maltase breaks down maltose and
Cellulase breaks down cellulose.
For desizing starch, amylase and maltase are used.

WORK OF ENZYMES
Amylase will degrade starch into
maltose, a water soluble disaccharide
and Maltase will convert maltose into
glucose, a simple sugar.
Starch ----------> Maltose -------->Glucose
Amylase Maltase

Quality control check
Desizing efficiency test
Iodine test
Fluidity test

JIGGER
A Jig or Jigger is a batch
machine which handles
fabric in open width. It is
a simple machine consisting
of let-off and take-up rolls, a
trough containing the
processing liquor and guide
rolls which allow the fabric
to pass from the let-off to
the
take-up roll.

Scouring
It is process to remove all undesirable
impurities (Natural: like dirt, vegetable
matter, grease wax etc and Added: like
remaining size material, stains etc.)
Natural Impurities: Based on the
composition of natural material like cotton,
wool, silk etc.

SCOURING
Natural fibers contain oils, fats, waxes, minerals, leafy
matter and motes as impurities that interfere with dyeing
and finishing.
Synthetic fibers contain producer spin finishes, oils and/or
knitting oils, grease.
These impurities are not soluble in water, they can be
removed by Extraction, dissolving the impurities in
organic solvents, Emulsification, forming stable
suspensions of the impurities in water and Saponification,
Converting the contaminates into water soluble
components.

Objectives
To make the fabric highly hydrophillic.
To remove impurities such as oil, wax, gum,
husk as nearly as possible.
To increase absorbency of fabric or textile
material with out physical or chemical change.
To produce a clean material by adding alkali to
make the fabric ready for next process.
To remove non cellulosic substances in case of
cotton.

The change occurring of
cotton fibres during scouring

Chemical used in scouring
process

Form of scouring
Yarn scouring :
Hank
Package
Fabric scouring : open width
Jigger
Pad batch
Rope form
Kier

Methods of scouring
There are two principal methods of
scouring
Discontinuous method (winch , jigger
kier)
Continuous method (scouring in j box )

Difference between scouring
and souring

SOLVENT SCOURING
Certain organic solvents will readily
dissolve oils fats and waxes and these
solvents can be used to purify textiles.
Removal of impurities by dissolution is
called Extraction.
There are commercial processes where
textiles are cleaned with organic solvents.
Fabrics processed this way are said to be
"Dry Cleaned".

Bleaching
This is a process of whitening-fibers, yarns,
or fabrics having natural colour.
It is carried out by using oxidising agents
like
Sodiumhypochlorite (NaOCl)
Hydrogen peroxide (H2O2)
Sodium Chlorite (NaClO2)

The color producing agents in natural fibers
are often organic compounds containing
conjugated double bonds.
It is known in dye chemistry that
conjugation is necessary for an organic
molecule to perform as a dyestuff.
Decoloration can occur by breaking up the
chromophore, most likely destroying one
or more of the double bonds within the
conjugated system.

Bleaching
Oxidative bleaches oxidize color bodies into
colorless compounds. For example, double
bonds are known to be oxidize into epoxides
which easily hydrolyze into diols.
The major bleaching agents used in textile
preparation are sodium hypochlorite,
hydrogen peroxide and sodium chlorite.

52
Sodium Hypochlorite
(NaOCl)
Sodium hypochlorite is made by bubbling
chlorine into a solution of sodium hydroxide.
 when acid is added to a hypochlorite solution,
chlorine gas is liberated.
HOCl is active bleaching agent (hypochlorous acid )

Antichlor
Fabrics bleached with hypochlorite will
develop a distinctive chlorine odor.
This odor can easily be removed with
an aftertreatment consisting of sodium
bisulfite and acetic acid.

Souring
After the sodium hypochlorite bleaching
some CaCl2 , MgCl2 and other miniral
matter live in fabric. After that the fabric
feels harsh and stiff.
To reduce these chlorides fabric treat with
Hcl or sulphuric acid.

H202 Bleaching
Hydrogen peroxide was first used to
bleach cotton in the 1920's.
By the invention of the J-box which
lead to continuous processing.
Today, it is estimated that 90 to 95 %
of all cotton and cotton/synthetic
blends are bleached with hydrogen
peroxide.

Mechanism
Hydrogen peroxide is a weak acid and
ionizes in water to form a hydrogen ion and a
perhydroxyl ion.
The perhydroxyl ion is the active Hydrogen
peroxide can also decompose. This reaction
is catalyzed by metal ions e.g. Cu++, Fe+++.
This reaction is not desired in bleaching
because it is an ineffective use of hydrogen
peroxide and causes fiber damage.

Effect of pH
At pH < 10, hydrogen peroxide is the major specie
so it is inactive as a bleach.
pH 10.2 to 10.7 is optimum for controlled
bleaching. Sodium hydroxide is used to obtain the
proper pH.
At pH > 11, there is a rapid generation of
perhydroxyl ions. When the pH reaches 11.8, all
of the hydrogen peroxide is converted to
perhydroxyl ions and bleaching is out of control.

Stabilizers
Stabilizers must be added to the bleach solution
to control the decomposition of hydrogen
peroxide.
Stabilizers function by providing buffering action
to control the pH at the optimum level and to
complex with trace metals which catalyze the
degradation of the fibers.
Stabilizers include sodium silicate, organic
compounds and phosphates.

Sodium Silicates
Sodium silicates are the most commonly used
and most effective hydrogen peroxide bleach
stabilizers.
silicates have a natural affinity for ferrous ions
and ferrous ions are naturally present in cotton.
The silicates are adsorbed onto the ferrous ions
in the fiber, producing a species that
catalytically enhances bleaching while reducing
bleach decomposition and fiber damage.

Test For Degree of Bleaching
Whiteness Index-CCM

Whiteness
The standard ceramic tile is measured
and set to equal 100. The other
specimen are rated against this
standard.
Unbleached fabrics will give values in
the 50 to 60 range.
Well breached fabrics will rank 95 or
better.

OPTICAL BRIGHTENERS
Certain organic compounds possess the property of
fluorescence which means that they can absorb shorter
wave-length light and re-emit it at longer wave-lengths.
A substance can adsorb invisible ultra-violet rays and re-
emit them within the visible spectrum. Therefore a surface
containing a fluorescent compound can emit more than the
total amount of daylight that falls on it, giving an intensely
brilliant white.
Compounds that possess these properties are called
Optical Brighteners or OBA's.

OBA
If brilliant white finish is required in textile,
then bleaching is not sufficient. For this
purpose Fluorescent brightening agents are
used.
For synthetic fibres-OBA –Optical
Brightening Agents are mostly used.

• Fluorescence is the ability of a
substance to absorb radiation of light
and re-radiate it at a longer wavelength.
Incident light
Visible
U.V
Fibre without FBA Fibre with FBA
Eye detect visible
only
Reflected
UV & Visible
Eye detect visible & UV
both
Reflected Visible
Plus UV converted
to visible
Incident
light
Fluorescent brightening
agent(FBA)

OBA /FBA /BA
Optical brightening agents are based on (DAST)
diamino stilebenedisulfonic acid
Oba absorb ultraviolet light to within the range
of 350 to 360nm and reemit the absorbed energy
at 400 t0 500 nm with a maximum wavelength
at 430nm.
Due to presence of sulphonic acid group present
in OBA structure contribute to water solubility.

Properties of OBA
Mostly they are anionic in charge
(negetive )
pH typically between 8.5 to 11.0.
OBA addition will impart
Brightness
Whiteness
b* value(+b-yellow,-b blue )
Lvalue
a* value (lower green), (-a red)

Types of OBA
Basic classes of chemicals used in OBAs
include:
Triazine-stilbenes (di-, tetra- or hexa-
sulfonated)
Disulphonated (cellulose)
Tetrasulphonated (universal)
Hexasulphonated
Coumarins
Imidazolines

68
The Examples of preparation processes
of cotton and its blends fabrics
100% Cotton fabrics
1. Singeing
2. Desizing (only for woven fabrics)
3. Scouring
4. Bleaching (only for pale or bright shades)
5. Mercerizing
6. Adding of Optical Brightening Agent

69
100% Silk Fibers
1. Degumming (to get rid of non-fibrous
materials (sericin))
2. Bleaching (to make the goods whiter)

70
100% Wool Fibers
1. Carbonising (to remove leave, bark
and other parts of the plants from the
wool fibers)
2. Scouring (to get rid of fat and oil from
the fibers)
3. Bleaching (to make the fibers whiter)

Scouring of Wool
• Wool is a protein fibre
and sensitive to bases.
Wool can be scoured by
using detergent at pH
upto 7 at 60o
C
• To remove vegetable
material it is carbonised
by using Dilute
Sulphuric acid.
• It has tendency of
felting

Carbonising of wool
• Carbonising is a chemical treatment of
wool with strong acid (H2SO4)designed
to remove any remaining vegetable
impurity.

Felting and milling
• Felting is the tendency of the fibres to form
matted entanglements such that a woven
fabric, for example, can become so matted
that the warp and weft yarns are no longer
visible.
• The result is a fabric which is apparently
composed entirely of a entangled web of
fibres and the fabric is referred to a felt.
• Milling is the process of deliberately felting
wool goods to achieve the effects of felting.

Natural Impurities-Silk
• Silk contain 22 to
25% gum

Scouring of Silk
De-gumming:
• It is scoured by using
Soap and soda ash
• Treatment for 1 hour at
50o
C (repeat this
process three times)
• Bleaching is carried out
with hydrogen peroxide
(No NaOH) With
sodium silicate

Mercerization
This is the process applicable only on
cellulosic fibres especially cotton.
The main purpose of mercerization is to
alter the chemical and physical properties
of the fibre.

Change in cross section
1.Cross section of cotton before mercerisation
2-5 swelling process in 18% NaOH
6
6 Rinsing process after swelling
7 Final state
Change in cross section

Mercirization /Causticization
Both Mercerization and causticization require cotton
to be treated with concentrated solutions of sodium
hydroxide (caustic soda).
Mercerization requires higher concentrations of
caustic soda (19 to 26 % solutions) whereas
causticization is done with concentrations ranging
between 10 to 16%.
One major difference between the two is that
causticizing improves the dyeing uniformity and dye
affinity of cotton without improving luster.

Mercirization / Causticization
Caustic soda solution swells cotton fibers breaking
hydrogen bonds and weak van der Waal forces
between cellulose chains. The expanded, chains
rearrange and re-orient and when the caustic soda is
removed , the chains form new bonds in the
reorganized state.
When done tensionless, the cotton fiber swells, the
cross section becomes thicker and the length is
shortened. Because of fiber thickening, the fabric
becomes denser, stronger and more elastic.
Under tension, The fibers become permanently round
and rod like in cross section and the fiber surface is
smoother, adding to fiber luster.

Objectives
improved luster
increased ability to absorb dye
improved reactions with a variety of
chemicals
improved strength/elongation
improved smoothness
improved hand

Procedure
If cotton is dipped into a strong alkaline
solution such as lithium hydroxide, caustic
soda, or potassium hydroxide,The fibers will
swell and shrink.
If the fibers are placed under tension while in
this swollen state and then rinsed with water,
the alkali will be removed and a permanent
silk-like luster will result.

Effect of alkali on cotton fibres

PHYSICAL CHANGE
Improved in strength
Improved in lusture (under tension)
Change in cross section from bean
shape to almost circular
change in longitudinal view
convoluted to cylinderical

Chemical change
Improvement in moisture regain
improvement in dye uptake
Formation of celluloseII

Mercerising can be carried out on yarn
in hanks, woven and knitted fabric
through one of the following different
treatments:
· mercerising with tension
· caustification (without tension)
· ammonia mercerising.

Ammonia mercerising
Cotton yarn and fabric can be treated with
anhydrous liquid ammonia as an alternative to
caustic soda.
Effects similar to mercerising are obtained,
although the lustre grade is inferior to caustic
soda mercerising.
Traces of ammonia have to be removed,
preferably with dry heat treatment followed by
steaming. This method is not widely used. Only a
few plants are reported to use ammonia
mercerising in Europe.

Mercerization methods
Tension Mercerization (treatment
under tension)
Slack Mercerization (treatment
without tension)

Mercerization machines
Yarn mercerization
Fabric mercerization
Fabric mercerization:
Pad chain type mercerization
Pad chainless type mercerization
Padless chainless type mercerization

Test for Mercerization
Barium Activity Number
AATCC Test Method 89 is a common
test used for quantifying the degree of
Mercerization.
It is based on the fabric‘s ability to
absorb barium hydroxide. The
procedure is carried out on the fabric
both before and after Mercerizing and
the barium number is calculated as
shown below.

Test for Mercerization
Unmercerized fabric will give a barium
number of 100 to 105. Completely
mercerized fabric will give a barium
number of 150.
Commercially treated fabrics fall in a
range between 115 to 130.

Yarns are Mercerized as continuous sheets in a fashion similar to
woven fabrics. Greige yarns enter the caustic saturator and are held so
they do not shrink until the caustic has been washed out.
Afterwards, the yarns are dried continuously and wound onto bobbins
or spools. These conditions will develop satisfactory luster, elasticity
and dyeing properties; however, if higher luster and strength is desired,
the
yarns should be stretched beyond the greige length during the
process. Increase stretch, however, reduces dye affinity and elasticity.
The reasons for mercerizing yarns are:
1. To produce lustrous, strong 100 % cotton sewing thread.
2. To produce yarns for constructions that are difficult to
mercerize.
3. To produce yarns for special construction effects.
4. To produce yarns for blends containing fibers too sensitive
formercerizing.

Work Procedure
In natural condition the cotton fiber is a flat, twisted,
ribbon-like filament. When immersed in caustic solution it
swells out and takes on a round and a hair like appearance,
and becomes plump instead of flat.
How it is done
The cotton is soaked in strong caustic soda or
caustic potash solution for a few moments
under stretch and then washing in pure water
to remove the caustic.
trong caustic soda or caustic potash solution for a few moments under stretch and then washing in pure wat

The cellulose is changed into hydro-
cellulose or cellulose-hydrate.
Cellulose cannot be dyed so easily. Hydro-
cellulose on the other hand, absorbs almost
any kind of dye readily.
Mercerised cotton takes dyes so fast, that
chemicals are added in the dye bath to
check the process in order that the dyes
may not enter so rapidly as to render the
shading uneven.

Taking a cotton blend, and then
mercerising will produce an effect called
as crepon effect. Similarly,
mercerisation can be used to produce
seersucker effect by Mercerising only
certain stripes on the warp direction by
covering the rest of the cloth by suitable
means.

02 - Process sequence of wet processing.pdf

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