chemical finishing of textiles

CHEMICAL FINISHING OF TEXTILES

BY :TESFAY GEBREKIROS TSEGAY

AKSUM UNIVERSITY

DEPARTMENT OF TEXTILE ENGINEERING

2008 E.C

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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