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CHEMICAL FINISHING OF TEXTILES
BY :TESFAY GEBREKIROS TSEGAY
AKSUM UNIVERSITY
DEPARTMENT OF TEXTILE ENGINEERING
2008 E.C
22
INTRODUCTION Chemical Finishing refers to the use of chemicals to
achieve a desired end-use property.
Processes that change the chemical composition of
the fibers OR improve the surface characteristics
Can be applied in yarn, fabric, and garment stages
Can be durable or on durable based on resistance to laundering
Chemical finish is solution or emulsion of active
chemical in water
Wet Finishing
METHOD OF APPLICATION
EXHAUST APPLICATION
PAD-DRY-CURE --- Most widely used
Chemicals that have strong affinities for fiber surfaces can be applied in batch/discontinuous processes by exhaustion
Chemicals that have low/no affinity for fibers are applied by continuous processes that involve padding with chemical solution, squeezing, drying and curing for fixation
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By passing fabric through chemical finish
solution by ‘wet on dry’ process.
Factors affecting wet pick up:
Fiber, yarn and fabric characteristics
Machine settings [e.g. Squeeze pressure]
Solution properties [Viscosity, surface tension]
PAD APPLICATION OF CHEMICALS
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PAD-DRY-CURE
HIGH WET PICKUPS [70–100 %] IN PADDING TECHNIQUES
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Removal of large amount of water
during drying
Migration leading to uneven finish
distribution
For consistent chemical
application: Nip pressure should be uniform across the
fabric width
Solution level & temperature in pad
should be constant
Fabric speed should not vary throughout
the application
Wet pickup’ (wpu): amount of finishing solution applied
Add on: amount of supplied chemical added to the fabric
gpl to weight percent concentration
IMPORTANT CONCENTRATION RELATIONS
Feed rate to maintain constant liquor level in the pad
A cotton fabric is to be treated with 5.0 % on weight of fabric (owf) with a chemical finish in a wet on dry padding process. If the wet pickup is 90 %, what concentration of chemical is needed?
If the solution density is 1.05 g ml–1 ,what is the required concentration in g l–1?
If the fabric with linear density of 0.250 kg m–1
has a speed of 80 m min–1, what is the flow rate
of solution necessary to maintain a constant
level in the pad?
The same fabric is to be treated with 5 % owf of same chemical finish in wet on wet pad application with entry wet pickup of 75 %, exit wet pickup of 90 % and interchange factor of 0.7. What is the effective wet pickup?
WET ON WET APPLICATION
wpu0 is percentage wet pickup of fabric exiting the pad
wpui is percentage wet pickup of fabric entering the pad
f is the interchange factor, a measure of interaction between
incoming water and the pad solution (0-1)
ECONOMICAL AND ENVIRONMENTAL IMPACT
REDUCTION OF APPLIED WATER
LOW WET PICKUP METHODS
PAD APPLICATION?
Two main types of low wet pickup applicators.
With the first type fabric is completely saturated with the finish liquor and then the excess liquor is removed
SATURATION REMOVAL
With the second type, a precise amount of finish liquor is uniformly applied to the fabric
TOPICAL APPLICATIONHowever, too low a wet pickup can be equally problematic and also lead to uneven finish distribution if the liquid phase is discontinuous.
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VACUUM EXTRACTION
PULLING A VACUUM THROUGH THE WET FABRIC
MACHNOZZLE SYSTEMHIGH PRESSURE STEAM TO PUSHOUT EXCESS LIQUID
KISS ROLLThe kiss rol l picks up the chemical finish and transfers it by direct contact to the fabric.
Triatex MA (minimum application) system
Measurement of mass per unit area based on the intensity of electrons that pass through the fabric. The kiss roll rotational speed is automatically adjusted relative
to the fabric speed to maintain the desired wet
pickup.
LOOP TRANSFER SYSTEM
LOOP OF FABRIC IS IMMERSED IN FINISH LIQUOR, AND SQUEEZED WITH FABRIC TO BE TREATED BETWEEN SQUEEZE ROLLERS.
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Engraved roll transfer precise amount of chemical finish to fabrics; a doctor blade for removal of excess liquid from the roll surface
ENGRAVED ROLL APPLICATOR
MULTIPLE ROLLS FOR FABRICS WITH DIFFERENT WET PICK-UP
SPRAY APPLICATOR
Avoid overlapping spray patterns that could lead to an unacceptable uneven finish distribution
FOAM FINISHING
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By replacing part of water in chemical formulation with
air, amount of water added to fabric can be reduced.
Surfactants are included in formulation to be foamed.
The ratio of liquid to air in a foam is referred to as the ‘blow ratio’.
Foam densities 0.1 g cm–3 are routinely used
One side and two side foam applicators
The one side applicators apply foam to only one side of the fabric, leaving open the possibility of two different finishes on different sides of the same fabric.
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Two slots to apply the foam to the fabric. Two distinctly different finishes can be applied to different sides of the same fabric
DRYING WET TEXTILES
Water in a wet textile resides in three different areas.
Loosely bound water is on fabric surface /interstices.
Much of this water is taken out by mechanical means such as squeezing, centrifugation or vacuum
extraction.
Remaining water, water held in the yarn capillaries and water absorbed internally by the fiber, must be removed
through vaporization by thermal means.
STEAM HEATED CYLINDER DRYER
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HOT AIR STENTER
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CURING CHEMICAL FINISHES
Fixation of chemical finish for the desired final
property
Thermal treatments are used
Using the same heating equipment in drying of
textiles