UNIT-1:Natural and added
impurities in Textiles etc.
• The impurities that present naturally in the
plants/fibre (cotton, Wool, Silk etc) are called
natural impurities in wet processing points of
view as these impurities hinder the further
processing of fibres.
• Natural Impurities in cotton
• Natural Impurities in wool
• Natural impurities in silk
Natural Impurities in Cotton
Waxes and fats 0.5 - 1%
Proteins 0 - 1.5%
4 - 6%
Ash 1 - 1.8%
Structure of cotton fibre
• Structure differentiated into concentric zones
and a hollow central core known as lumen.
• The outermost layer is known as the cuticle and
is a thin film of fats, pectins and waxes
• Beneath this is the primary wall, composed
mainly of cellulose in which the fibrils are
arranged in a criss-cross pattern.
• Further toward centre is the secondary wall
composed of cellulose which constitutes the bulk
of the fibre.
• The secondary wall is differentiated in to three
zones S1, S2 and S3.
• S1= Outermost, thin layer fibrils periodically
reverse the direction of the spiral.
• S2= Accounts for the bulk of the cellulosic
content and in this case the fibrils are again in
the form of helices with a somewhat lower pitch
of 20o and 30o.
• S3= Found in mature cotton and adjacent of the
lumen and consists of the mineral salts and the
• It is an insoluble substance which is the main constituent of
plant cell walls and of vegetable fibres such as cotton. It is a
polysaccharide consisting of chains of glucose monomers
• Cellulose is an organic compound with the formula (C6H10O5)n,
a polysaccharide consisting of a linear chain of several
hundred to many thousands of β(1→4) linked D-glucose units
β(1→4) linked D-glucose units
(flavus = yellow)
Molecular structure of the flavone
Scouring of Wool
• Wool is a protein fibre and
sensitive to bases. Wool
can be scoured by using
detergent at pH up to 7 at
• To remove vegetable
material it is carbonised
by using Dilute Sulphuric
Detachment of Oil from wool by action of detergent
• Silk contain 22 to 25%
Scouring of Silk
• It is scoured by using Soap
and soda ash
• Treatment for 1 hour at
50oC (repeat this process
• Bleaching is carried out
with hydrogen peroxide (
NaOH is not used) With
• Oil used during spinning,
• Stains during spinning and fabric forming
• Sizing material during weaving
To dye or print textile material it is
needed to remove these impurities:
Process Called Preparation
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
Objective of Pretreatment:
• To Convert fabric from hydrophobic to
• To remove dust, dirt etc from the fabric.
• To achieve the degree of desire
Main steps of preparations
• It is a process to remove protruding fibres
from the surface of fabric using flame
• Singeing is a process of burning protruding
fibres from a textile structure
• This is a process of removing sizing chemical
i.e added impurties (added during weaving
process) from the fabric so the fabric can
• It is the process to remove natural impurities
present in the natural fibres (like cotton, wool,
silk etc) such as wax, pectine, coloour, gum
• It is the process to make textile fabric white.
Various types of bleaching agents- Oxidising or
reducing may be used
• In this process the cellulose material mostly cotton
yarn or fabric is treated with high concentration of
sodium hydroxide. With this process following effects
are observed in the cotton:
• Improved luster
• Improve absorbency
• Improve reactivity with chemicals
• Improve stability of form
• Improve smoothness
• Improve hand
• It is a process of steaming woll or its blends to set
the fabric and reduce shrinkage and creasing. It is
a finishing process in which the fabric is wound
tightly onto a perforated roller and either
immersed in hot water, which is also circulated
through the fabric (Wet decatising) or has steam
blown through it (dry decatising).
• It is used mainly to improve the handle and
appearance or worsted fabrics.
PROCESS SEQUENCES OF CHEMICAL
Grey fabric Inspection &
Soaping & Drying
Folding & Packing
• Following are the steps to be taken
before going wet processing :
Shearing and cropping
Typically a woven
cotton fabric would be
prepared by sequence
of process as shown.
In case of knitting
sizing step is not
• Grey stage fabric usually 60-70 m in
length so that several pieces are stitched
together to make a processable length (
Lot size ).
• Normally Polyester ( Sewing thread ) yarn
is used for stitching
Precautions before stitching
• Marked each piece properly for sort number,
lot number etc. so that piec can be identify at
any stage of the processing
• Two pieces are arranged selvedge to selvedge
and the ends are stiched on a special end to
end stitching machine so that pieces are
joined without overlapping
Stitches & Stitching threads
• Cotton threads: 3/40s, 4/30s, 4/36s, 6/28s
and 6/36s are popular
• Polyester threads are also used when
carbonising is required
• Stitches per inches: 6 to 7 for coarse, 7 to 8
for poplin and 8 to 10 for cambric
• Due to difference in width
of the pieces
• Some time careless
handling also lead to a
Causes: Fold or selvedge
crease and the fold
portion either less dyed or
• Pieces are not locked in the
stitch at and near the
• Due to careless handling
Causes: Such stitch will open
out more and more every
pull around guide roll during
processing. It may induce
Fold or crease formation at
undyed/unprinted folds will
• Due to careless handling
Causes: It may cause thread
mark in dyeing and
entanglement in machine
parts, etc. The loose
thread may pick up soil
and damage long lengths
• If the large folds are
inserted in the stitch to
difference of two pieces,
it will surely lead to
Causes: It may cause warp
stripes in dyeing and
creases in dyeing and
• It may be due to poor
poor quality of thread
or poor method of
Causes: It may cause
damage in dyeing and
SHEARING & CROPPING
• In shearing ,the fibres are cut in an angular manner
on the surface of the fabric itself, resulting in a
• 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
Singeing is a
process of burning
from a textile
Rotary (Roller)-cylinder singeing m/c
In this type of singeing machine, the cloth passes over and in
contact with a heated rotary cylinder made of copper or cast
The rotary cylinder has internal firing and revolves slowly so
that constantly a fresh surface of the roller comes in contact
with the cloth.
The direction of rotation of the cylinder is opposite to the
direction of the fabric so that the protruding fibers or nap of the
fabric is raised.
This type of machine is particularly suitable for the singeing of
velvets and other pile fabrics.
If the singeing of both sides of the fabric is required, then two
cylinder are employed, one for each side of the fabric.
In this type of singeing machine, the cloth passes over and in contact
with one or two heated curved copper plates.
The thickness of the plates ranges from 1 to 2 inches. The heating of
the plates is done by a suitable burning arrangement of gas mixed with
The plates are heated to bright redness and the cloth passes over and
in contact with these plates at a speed ranging from 150 to 250 yards
per minute, the protruding fiber are burnt during the passage.
The fiber end present in the interstices of warp and weft are not
singed, since they are not made accessible
Due to contact between the cloth and a hard and hot surface of metal
a certain amount of luster in the cloth is produced.
Disadvantage: It may be not possible to maintain the plates at uniform
temperature and this cause uneven singeing.
Gas singeing machine
In this type of singeing machine, the fabric passes over a burning
gas flame at such a speed that only the protruding fibres burn and
the main body of the fabric is not damaged by the flame. This is the
most common type of machine used for singeing fabrics as well
Important GAS singeing parameters
Following are the important gas singeing parameters:
Distance between flame burner and fabric
The flame intensity of the singeing burners is based on
the amount and the outlet speed of the gas-air mixture leaving
the burner slots.
Besides having high thermal energy, flame also has
considerable mechanical energy.
All the thermal and mechanical energy of the flame is
directed onto the fabric during singeing.
The temperature of the flame at the mouth of the burner is
in the range of 1250 to 1300oC.
The speed of the flame at the burner outlet may be
between 15 and 35 meter per second.
The flame intensity usually lies between 5 and 20 mbars.
The fabric speed in the singeing machine is usually in the
range of 50-160 m/min depending on fabric (gram per
square meter) weight and fibre blend. For heavier fabrics,
the speed is kept slower as compared to lighter weight
This is the most intensive singeing position with highest efficiency.
In this position, the flame bounces onto the free-guided fabric at right angles.
This position is usually recommended for singeing of fabrics with all natural fibres (e.g.
cotton), regenerated fibres and blended fabrics, which have been tightly woven and have
weights over 125 g/m2
1. Singeing onto free-guided fabricWatercooledroller
2. Singeing onto water-cooled roller
In this position, the flame bounces at right angles onto the fabric while the
fabric passes onto water-cooled guide roller.
This position avoids the penetration of the flame into the fabric.
The flame does not pass through the fabric, and because of the fabric passing
onto water-cooled roller, any thermal damage of temperature-sensitive synthetic
fabrics is avoided.
This position is usually recommended for all blended and synthetic fabrics as
well as for fabrics having weights less than 125 g/m2 and fabrics with open
3. Tangential Singeing
In this position, the singeing flame falls on the fabric tangentially.
The flame touches only the protruding fibres without having any significant contact
with the main fabric body.
This position is usually recommended for very light weight and sensitive fabrics as well
as fabrics with broken filaments.
Distance between Flame Burner and Fabric
As the energy content of the flame is lower the
farther it is from the burner, the singeing efficiency
is consequently decreased by increasing the
The distance between the burner and the fabric
is usually in the range of 6-8mm but it can be
adjusted in a range from 6-20mm.
All good singeing machines come with a provision of flame
width adjustment according to the width of the fabric. This is
essential to optimize the gas economy
Essential conditions for good GAS
Following are three essential conditions for good singeing:
A flame with high mechanical & thermal energy quickly burn
thermoplastic protruding fibres (e.g. polyester) without any
molten beads formation
A homogeneous flame with uniform mechanical & thermal
energy to result in uniform singeing
An optimal flame/fabric contact time to neither result in
incomplete not over-singeing
Testing singeing effectiveness
The effectiveness of singeing process can be checked by one
or more of the following:
By looking at the singed fabric with magnifying glass and
comparing its hairiness with that of the un-singed fabric. A
well-singed fabric shows less hairiness.
By testing the singed fabric for pilling performance and
comparing it with that of the un-singed fabric. A well-singed
fabric gives less pilling.
By sticking and removing a sticking tape on the singed
fabric and observing the number of fibres attached to the
sticking side of the tape. A well-singed fabric results in less
number of fibres sticking on the tape.
Noticing the feel or handle of the singed fabric. An over-
singed fabric may give a harsher feeling.
It is an enzyme treatment designed to
improve fabric quality and provide
• Improve pilling resistance
• A clear, lint and fuzz-free surface
• Improved drape and softness
• The effect are durable
• Cellulase enzyme is used
• Enzyme dosage 1-2% owf
• pH 4.5-5.5
• Temperature 40-55oC
• Time 30-60 min.
It is similar to singeing as it also
provide similar effect on the fabric.
Fig. 7. Carbomatic®
Singeing Line by
Fig. 8. DORNIER
singeing machine for
circular knitted fabrics
What should control during
• 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
1. Wool grease can be removed by scouring. These
Grease/waxes are comprised of a variety of monocarboxylic,
dicarboxylic and hydrocarboxylic acids as well as steroidal
alcohols. It has been determined that unscoured wool contains
an unoxidized fraction of wool grease and other contaminants
that is easily removed and readily recoverable
2. Suint is usually considered to be a variable composition of
water-soluble materials that is readily removed by scouring.
3. The dirt that is removed from the scoured wool consist of both
inorganic and organic materials
• Suint: It is dried perspiration and soluble in water.
Simple washing in detergent removes suint.
• Wool fat or wool wax: It is complex mixture of
esters, diesters and hydroxyesters fatty alcohol
like lanoline and fatty acid. It is hydrolysed in the
presence of mild alkali like ammonia at moderate
temperature. Wool wax can be isolated and used
in preparation of good quality soap and
• Dirt: It is held by adhesive action of suint and
wool fat. It removed during the scouring and
Burrs: It is vegetable fragments consisting of
dried grass, straw, sticks etc. These vegetable
fragment come on the body of sheep during
grazing and scratching the body against bush
or tree to relive itching.
Removal of Vegetable matter
(Carbonization of wool)
• Wool is resistant to acid. Burr being a
vegetable matter is not resistant to acid.
• This property is used for the removal of burr.
• In this case wool is treated with 5-7%
Sulphuric acid for 2 hours followed by hydro-
extraction and then drying at 80-90oC for 20-
• Carbonized burr is removed by washing with
• Decatising or decatizing, also known
as crabbing, blowing, and decating, is the process of
making permanent a textile finish on a cloth, so that it
does not shrink during garment making.
• The word comes from the French décatir, which means
to remove the cati or finish of the wool.
• Though used mainly for wool, the term is also applied to
processes performed on fabrics of other fibers, such
as cotton, linen or polyester.
A finishing process in which the fabric is wound tightly onto a perforated
roller and either immersed in hot water, which is also circulated through
the fabric (wet decatising) or has steam blown through it (drydecatising).
•Decatized wool fabric is interleaved with a cotton,
polyester/cotton or polyester fabric and rolled up onto a
perforated decatizing drum under controlled tension. The
fabric is steamed for up to ten minutes and then cooled
down by drawing ambient air through the fabric roll. The
piece is then reversed and steamed again in order to
ensure that an even treatment is achieved.
•There are several quite different types of wool decatizing
machines including batch decatizing machines, continuous
decatizing machines, wet decatising machines and dry
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