fabric pretretment 1

7/28/2019 Fabric Pretretment 1

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Introduction to Textile Preparation

Ashish gupta


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Basic Textile Definitions

Fibers = A smallest unit of textile materials.

Usually classified by flexibility, fineness, anda ratio between length and diameter (L/Dratio)

Natural Fibers = Fibers that come fromanimals (wool, silk etc.), plants (cotton, flax,hemp, jute etc.) or mineral material(asbestos).

Synthetic Fibers = Man-made fibers or

artificial fibers which is usually comes fromchemical agents.


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Semi-synthetic Fibers = Fibers that comes

from solutions of natural polymer or

derivatives from the natural polymer(cellulose, protein etc.)

Polymer= Macro molecules containing

small chemical units (named Monomer)


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Staple Fibers = Fibers from natural or

synthetic fibers which were cut into short

fibers. Normally, natural fibers are staplefibers (expected silk fibers). These fibershave 5-500 millimeters long.

Filament Fibers = Fibers from natural or

synthetic fibers which have infinite length.

Silk Fibers are the only one natural fibers

classified in this definition since their length

between 700-1500 meters depending to theirraces.


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Yarns = The combinations of fibers using

some twisting (Z and S twists) in order tomake strong and stable yarns.

Spun Yarns = The yarns that come formstaple fibers.

Filament Yarns = The yarns that come from

filament fibers (mono-filaments and multi-filaments)

Fabrics = The products of weaving, knitting

or non-woven processes. Normally, fabricshave a certain thickness and can withstandtear and tensile forces.


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Morphology of Textile Fibers

1. Crystalline Regions are the regions that

cannot absorb water, humidity and dyestuffsolutions but they are the part for fiberstrength.

2.Non-Crystalline Regions or Amorphous

regions are the regions that can absorb water,

humidity and dyestuff therefore they can be

dyed but they are a very weak part of the

fibers.


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3. Orientation of the Crystalline Regions

alongside the fiber axis

This property is very important in that it willincrease the tensile strength of the fiber if itpresents in the optimal quantity.

Crystalline

Amorphous Void space


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Textile Preparation is the heart of the textile

dyeing, printing and finishing processes

because fibers, yarns or fabrics have manyimpurities (i.e. cotton wax, starch, lubricant,

silk sericin, wool oil etc.) as a proverb Well

begin is half done. From the experience,more than 60% of the faults from these

factories come from preparation.


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The Examples of preparation processes ofcotton 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


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100% Silk Fibers

1. Degumming (to get rid of non-fibrous

materials (sericin))

2. Bleaching (to make the goods whiter)


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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)


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Singeing Process

Singeing is a process that uses gas flame or

hot plate in order to get rid of small fibersprotruding (hairs) on the fabrics (thesefibers normally come from spun yarns).

Objectives:1. To get rid of the small fibers

2. To make the fabrics smoother than before

3. To help the printing ink or dyestuff to

make clearer marks on the fabrics

4. To improve rubbing fastness and washing

fastness of the dyed or printed fabrics


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Singeing Process

The fabrics are passed over a heated copper plate or above agas flame. The fiber ends burn off.

The fabric is moved rapidly, and only the fiber ends are

destroyed. Immediately after passing the flame, the fabric

enters a water bath that puts out any remaining sparks. The burning characteristics of fibers must be taken into

account when this process is applied, as heat-sensitive fibers

melt, forming tiny balls on the surface of the fabric. These

balls interfere with dye absorption, so that, as a general rule,

heat sensitive fibers would be singed after dyeing or printing.

Filament yarns do not require singeing, as there are no short

fiber ends to project onto the surface of the fabric. Fabrics that

are to be napped are not singed.

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Types of singeing machines

Plate singeing

Roller singeing

Gas/Flame singeing machine

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Plate singeing

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Roller Singeing

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Flame Singeing

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Singeing handout

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http://localhost/var/www/apps/conversion/tmp/scratch_5/36996948-Singeing.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/36996948-Singeing.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/36996948-Singeing.pdf


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DESIZING

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Desizing process

This will get rid of the starch or size covering

the warp yarns using enzymes, oxidizing

agent, or other chemicals and ensures

levelness of the dyestuff or printing ink. If

not taken out completely, it will affectwashing and rubbing fastness of the fabrics.


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Where does starch come from?

Starch or Size is a material that help the

weavers to ensure that their warp yarns are not

broken or struggle with the reeds. Therefore

these will lead to low productivity and highmachine break-down rate.

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Desizing methods

Hydrolytic methods

Rot steep

Enzymatic steepAcid steep

Oxidative methods

ChlorineChlorite

Bromite


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Rot steep

Oldest, cheapest, no specialchemicals required

Warm water 40degC,allowed to stand for 24h

Micro-organisms, naturallypresent in water multiplyand secrete starch-liquefying (hydrolyzing)enzymes, which soubise thestarch present in the size

Disadvantages

slowprocess, requires enormousspace


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ENZYMATIC DESIZING

Enzymatic desizing is the process of

degrading starch size on cotton fabric using

enzymes. Enzymes are living micro-

organisms, that catalyze chemical reaction inbiological process. Enzymes are quite specific

in their action on a particular substance.


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Acid steep (Desizing)

Dilute sulphuric or hydrochloric acid (0.25%

w/v), room temp, time 8-12h

Hydrolysis of starch is an exothermic process

increases temp of cloth

hydrolysis increases

Higher concentration hydrolyze the cellulose

weakens cotton structure (can detect only

after dyeing or printing)


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OXIDATIVE DESIZING

In oxidative desizing ,the risk of damage to the

cellulose fiber is very high. Thats why this

process is used very rarely. Oxidative desizing

uses potassium or sodium persulfate orsodium bromite as an oxidizing agent.


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Bleaching

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Bleaching

To remove natural pectin ,wax ,protein ,coloring material and

unwanted minerals from the fabric. Even manufactured fiber fabrics, especially those that have

been heat-set, may become yellowed as a result of

processing. Therefore, fabrics may require bleaching or

whitening to prepare them for dyeing or printing or toproduce a clear white fabric

To make the substrate uniformly absorbent through out its

length and breadth.

To make the substrate uniformly white for pure white finisheswith optical brighteners or for subsequent dyeing, mercerizing

etc

Bleaches are chemical substances that oxidize colored

compounds, removing the color. 29


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Chemicals used

Hydrogen Peroxide (H202)

Cotton, Silk, Wool, Jute,

Sodium Hypo chloride (NaOCl)

Cotton


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Application

Most bleaches used by industry are either chlorine bleaches or

peroxide bleaches.

The peroxide bleaches, and particularly hydrogen peroxide

bleaches, are used most frequently in commercial bleaching of

greige goods, although for some fabrics other types ofbleaches must be used.

Mill processes include saturating the fabric with the bleaching

agent, steaming it to effect the bleaching reaction, and

washing the fabric thoroughly, usually with a dilute mineralacid to neutralize any residual alkali. This last step is called

souring and in earlier times was done with buttermilk.

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Carbonization


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Objective

Remove vegetable impurities such as plant stalks ,

seeds, motes and leaves often designated as burs.


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Process

Wool is saturated with a weak solution of sulphuric

acid or sometimes a solution of ammonium chloride

and is then hydro extracted to remove excess liquor.

Vegetable impurities will become so friable thatwhen the wool is led through a machine which

crushes and shakes it ,the disintegrated impurities

easily separate from it.


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Scouring

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Scouring

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Objectives1. To remove natural fat, wax, and oil

materials containing in the fabrics without

damaging the fibers2. To accelerate dye and chemical absorption

of the fabrics

3. To improve the handle of the goods (softer)


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Natural Impurities

Cotton may contain between 4 and 12% by weight of

impurities in the form of waxes, proteins, pectins, ash, and

miscellaneous substances such as pigments, hemicelluloses

and reducing sugars. These impurities are removed from thefabric by scouring, since their hydrophobic nature negatively

affects the enhancement of the fabrics wet ability and

absorbency.

Silk contains mainly silk gums.

Wool contains wool fat and perspiration residues.

Scouring removes waxes and destroys vegetable matter

residues in cotton and cotton blend fabrics.


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Scouring process

The scouring process employs sodium hydroxide or related causticizing

agents such as sodium carbonate, potassium hydroxide or mixtures thereof.

Generally an alkali stable surfactant(detergent) is added to the process to

enhance solubilization of hydrophobic compounds and/or prevent their

redeposition back on the fabric.

The treatment is generally at a high temperature, 80"C - 100"C, employingstrongly alkaline solutions of the scouring agent, e.g., pH 13-14 for 20-30

minutes.

For silk and wool mild base like Sodium carbonate is used.

Scouring was traditionally done in a kier vat, a large iron vessel in which

the fabric was boiled in the alkaline solution. Economic considerationshave largely caused this batch method to be replaced by continuous

processes. The fabric can be passed over a series of rollers in a pad bath, so

that it is repeatedly exposed to the scouring solution.


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Degumming

Silk that contains sericin is called raw silk.

The gummy substance affords protection during

processing and so is usually retained until the yarn or

fabric stage.It is removed by boiling the silk in a mildly alkaline

solution. This process, called degumming, leaves the

silk soft and lustrous, but it can reduce the weight of

the silk by as much as 30 percent.

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http://www.wormspit.com/degumming.htm

DEGUMMING
http://www.wormspit.com/degumming.htmhttp://www.wormspit.com/degumming.htmhttp://www.wormspit.com/degumming.htmhttp://www.wormspit.com/degumming.htm


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Mercirization

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Obj ti


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Objectives

1. To make the goods more luster because raw

cotton fibers are ribbon-like. After this

process, the fibers change to cylindrical shape

resulting more evenness reflected light fromthe goods.

Before After2. To improve dyeability of the goods about

5-10%.


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The change


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Benefits

Improve dye affinity and yield

Improve breaking strength

Improve dimensional stability Improve chemical reactivity

Improve fabric smoothness

Cover immature cotton fibers


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Process

The treatment consists of immersing the yarn or fibre ina solution ofsodium hydroxide (caustic soda) for short

periods of time, usually less than four minutes.

The material is then treated with water or acid to

neutralize the sodium hydroxide. The material is held under tension during this stage, it

is kept from shrinking appreciably; if no tension isapplied, the material may shrink by as much as one-fourth.

Higher-quality cotton goods are usually mercerized;cloths so treated take brighter, longer-lasting coloursfrom less dye.
http://www.britannica.com/EBchecked/topic/552224/sodium-hydroxidehttp://www.britannica.com/EBchecked/topic/552224/sodium-hydroxidehttp://www.britannica.com/EBchecked/topic/552224/sodium-hydroxidehttp://www.britannica.com/EBchecked/topic/552224/sodium-hydroxide


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Difference


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Causticizing (alkali treatment):

Similar effects to mercerising can be achieved by the

Causticizing process.

Causticizing in comparison to mercerising is done

without tension stress on the textile at temperaturesbetween 10 C and 15 C.

It gives a better handle than mercerized fabric.


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Adding Optical Brightening Agent

The process is to add special dyestuff into

textile or paper to make them brighter whenlooking at black-light light bulb or natural

sunlight. As the dyestuffs are colorless but

using UV light to excite these dyes. Theywill reflect the light at the wavelength that

human can see (i.e. blue, violet). So thegoods look brighter and whiter.

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