35048298 textile pre treatment right first time

8/4/2019 35048298 Textile Pre Treatment Right First Time

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Why do Pretreatment is

important?

Satisfactory preparation of the substratebefore dyeing and finishing makesmajor contributions to consistentattainment of the desired end-productquality.

well prepared is half-dyed


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Factor for Successful

Preparation of Textile

Successful preparation depends on 4 factors

the amounts of the various impurities present

the purity of the water supply

the chemicals used in the various preparation

processes the machinery available for processing of the

goods.


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Troubleshoot in pretreatment

:Factor to yellowing of textiles


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Water Specification for textile

wet processing


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Average water consumption

by fibre type


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Water consumption by process


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Preparation and Dyeing of

Cotton

Cotton Impurities and Preparation Chemicals Pectins are polygalacturonic acids and their calcium,

magnesium and iron salts.

The inorganic ash contains calcium, magnesium andpotassium phosphates and carbonates.

The spin finish and knitting oil contain mineral oil andsurfactants applied to decrease friction on machinery parts.

Sizing agents are film-forming polymers applied to warp

yarns before fabric weaving in order to minimise yarnbreakage.

Metallic ion contamination, particularly iron and copper, is ofserious concern during oxidative bleaching processes


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Composition by mass of a

typical cotton fibre


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Important factors to select and

use of surfactants in preparation

wetting agents used in the desizing stage must be compatible

with the enzyme preparation detergents selected for scouring must be stable at the

temperature and concentrations of alkali and electrolyterequired

surfactants added to bleach liquors must be stable to stronglyoxidising conditions residual surfactants which retaining must not cause problems in

subsequent printing or water-repellent finishing the cloud point of any nonionic surfactants used must be high

enough to avoid impairing the wetting or detergencyperformance

surfactants must be low-foaming to avoid risks of pumpcavitation in circulating-liquor systems and loss of traction in

conveyor or roller-bed steamers the viscosity of the surfactant solution should allow satisfactory

performance in automatic dosing systems.


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Sizing agents for different

substrates


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Desizing

Natural starch, starch ethers, celluloseethers and polyacrylates are usuallyused as sizes.

Economical starch-based formulationsare effective for cotton yarns

Poly(vinyl alcohol) is often preferred forsizing polyester/cotton blends

Waxy plasticisers may be added to the size mix.


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Factors for Size removal

concentration and viscosity of the sizeformulation

nature and amount of plasticiser

present fabric construction

ease of dissolution of the size washing-off procedure and

temperature.


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Enzymatic desizing

Amylase enzymes are highly effective catalysts forthe hydrolysis of the amylose and amylopectincomponents of starch size.

Normal type are applied for several hours at 65 to

70C Thermostable hydrolytic enzymes have been

introduced, allowing brief dwell times at

temperatures up to 120

C. Common salt and calcium ions increase the rate of

hydrolysis but amylase is deactivated by copper orzinc ions, as well as most anionic surfactants.

There is some interest in the use of pectinases as scouring agents andlignases to degrade the lignin in bast fibres, but as yet no commercialprocesses have been developed.


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Scouring is the hot alkaline process necessary to remove the

non-cellulosic impurities. The main effects of this treatment are a 5 to 10%

loss in mass and a dramatic improvement inwettability and absorbency.

The change in mass results from degradation ofprotein to amino acids, conversion of pectin tosoluble sodium salts, hydrolytic dissolution of

hemicellulose and a limited amount of oxidativedegradation of cellulose. Saponification of the cotton wax is incomplete but it

has to become no longer capable of forming a

continuous film over the fibre surface.


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Oxidative desizing reducing the number of fabric preparation stages, an

important means of minimising the overall energyconsumption.

The oxidant can be added to the hot caustic scourliquor and little or no magnesium silicate or organic

stabiliser is needed. Rapid desizing treatments require more critical

control of alkali and oxidant concentrations.

Increased oxidant above the minimum necessary foreffective desizing and increasing the alkalinity for agiven oxidant concentration both tend to increase thedegree of chemical damage.

Persulphates promote desizing rather than bleachingand require more critical control of concentrationthan does hydrogen peroxide.


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Bioscouring

Bioscouring is a process in which an alkali-stablepectinase enzyme is applied to selectively removepectin and waxes from cotton fibres.

By hydrolysing the pectin material between the

waxes and the fibre surface, the enzyme exposes thewaxes to emulsification when the scouring bathtemperature exceeds their melting range.

Bioscouring does not eliminate motes (cottonseedfragments) or the natural colour of the cotton, whichcan be beneficial when scouring for a natural look


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Hypochlorite Bleaching

Hypochlorite bleaches rapidly at ambient temperatures Less sensitive to transition-metal ions than peroxide but it does

easily chlorinate organics present, it will turn to yellows on greycotton by chlorinating the pectins and proteins.

Cotton must be cleared of natural impurities by thoroughscouring before bleaching. Must be followed by washing and an antichlor treatment with

bisulphite. Prolonged, labour-intensive batchwise process with relatively

low chemical costs but high water consumption. Chlorinated impurities are detected in effluent streams as

absorbable organohalogens (AOX) and chloroform, which areenvironmentally unacceptable.

For these reasons, Hypochlorite bleaching w ill be abandoned


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Advantages/disadvantages of

bleaching with hypochlorite


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Chlorite Bleaching Sodium chlorite is used under acidic conditions Bleaching can be carried out on grey or desized cotton. Acidic conditions removes only a small proportion of the natural

cotton wax, which can be advantageous in softening knitgoodsand knitting yarns.

Relatively unaffected by iron or copper contamination. Adequate fume extraction is essential, for ensuring protection

against evolution of toxic chlorine dioxide gas from the acidicchlorite solution.

The corrosive nature of this chemical demands exoticconstructional materials such as titanium. The AOX generated by chlorite is much less than the amount

generated by hypochlorite, but even this is more than twice thatpresent after bleaching with hydrogen peroxide


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bleaching with chlorite


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Hydrogen peroxide bleaching Hydrogen peroxide is an extremely versatile bleaching agent,

applicable over a wide range of temperatures (ambient to130C) and times (minutes to days) by batchwise or continuousmethods.

Bleaching is carried out under alkaline conditions and this allowscombined scour-bleach processes to be used.

Bleaching with hydrogen peroxide is controlled by adding astabiliser.

Organic stabiliser including magnesium salts and anionic polyelectrolytes such as silicates, polyacrylates protein degradation products sequestering agents to trap the transition-metal ions surfactants provide detergency during bleaching. Most of these products give adequate stabilisation in batchwise

conditions but stabilisation in continuous pad-steam processes ismore difficult.


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Factors for hydrogen peroxide

bleaching for cotton

exceptional versatility of application bybatchwise or continuous methods

a wide range of possible means ofactivation and stabilisation

exceptionally innocuous to the

environment, decomposing into oxygenand water.


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bleaching with hydrogen peroxide


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AOX values for cotton bleached

with various oxidising agents


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Mercerisation Mercerisation of cotton is achieved by saturation with

cold caustic soda solution at about 25% w/w andcontaining a good wetting agent. Swelling of the fibres takes place, accompanied by

shrinkage unless the fabric is held under tension.

Mercerisation may be carried out on the grey,scoured or bleached substrate. Grey mercerising also fouls the liquor with size

residues, causing instability and making caustic

recovery for recycling difficult. Mercerisation enhances fabric lustre, smoothness,

tensile strength, dyeability, dimensional stability andcoverage of dead cotton.

influenced by alkali concentration, temperature and dwell timein alkali prior to w ashing-off


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Preparation and Dyeing of

Regenerated Cellulosic Fibres Regenerated cellulosic fibres are desized by the same

processes as for cotton.

Care should be exercised with oxidative desizing interms of both alkali and oxidant concentrations,

which should be no more than half of those used forcotton.

Most warps contain starch-based sizes and soenzyme desizing is customary.

However, carboxymethylcellulose is sometimes usedand in this case a cold swelling process followed byhot washing with a detergent is adequate


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Tip for regenerated cellulosic

fibres preparation Viscose and other regenerated cellulosic fibres

dissolve in caustic soda liquor at about 6.5% w/w (70g/l), so causticisation rather than mercerisation iscarried out using 3.3 to 5.5% w/w NaOH (35 to 60g/l) to enhance wetting or dyeability.

The addition of salt minimises the risk of damage.However, causticisation can cause uneven swelling ofthe fibres and lead to unlevel dyeing.

Cellulase enzyme can widening of the voids in viscosefibres, making more internal surface available toalkali during swelling. A saving of 5 to 10 g/l causticsoda is attainable, as well as a more uniform andconsistent swelling effect


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Swelling action of regenerated

cellulosic fibres in alkali The swelling action of alkali on the strength and handle of

viscose is less pronounced with more tightly spun yarns andwoven fabrics. Better stabilisation is possible by fibre blending

for example, viscose can be dyed with vat dyes without difficultywhen blended with cotton or polyester.

Polynosic fibres are more resistant to alkali than regular viscose. Cotton/polynosic blends form an alkali-stable substrate that can

be mercerised. The strong swelling of viscose results in an increase in the

diameter of the fibre. Particular in the dyeing of cross-woundpackages.

For this reason, packages of viscose staple yarn must be w ound at alower tension than cotton yarn


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Silk Degumming Sericin forms the film outer covering of greige silk

and is classified as a kind of scleroprotein orprotective sheath.

The sericin content of the filaments varies accordingto their position within the cocoon, those in theoutermost layer having the highest content.

Sericin is not a homogeneous protein but can beseparated into four fractions on the basis of theirdifferential solubilities in hot water

Sericin and fibroin differ considerably in theirchemical composition and accessibility, sericin beingcomparatively easily accessible to degumming

chemicals


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Various methods for

degumming

aqueous extraction boiling-off in soap

degumming with alkalis enzymes

degumming in acidic solutions

Fully degummed silk, the degumming loss is 18 to 30%


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Silk bleaching normally carried out only for pale to medium

dyeings or fabric sold as white. Reductive bleaching with hydrosulphite can

be combined with alkaline degumming but it is more usual to give an oxidative

bleach separately after degumming. typical process would be for 2 to 4 hours at 70oC

or 1 to 2 hours at 80 to 85o

C, using 10 to 15 ml/lhydrogen peroxide (35% solution), 1 g/l EDTA(30% solution) and 3 g/l sodium pyrophosphate topH 9, followed by thorough rinsing.


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Traditional process sequence

for polyester fabrics


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Preparation of polyester An aqueous scouring bath containing 1-2 g/l anionic detergent

and 2 g/l sodium carbonate is satisfactory for most purposes Suitable detergents include fatty alcohol sulphates,

alkylarylsulphonates and their mixtures with ethoxylated fattyalcohols.

At the low liquor ratios applicable in scouring on the jig theseconcentrations should be increased threefold. The processing time and temperature may be adjusted

according to substrate type, the degree of contamination andthe available equipment.

Woven or lightweight knitted fabrics prone to creasing shouldbe treated in open width at 50 to 60C but many textured weft-knit qualities can be scoured in rope form for a shorter time atthe boil.

30 minutes at 60C is adequate in many cases


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Preparation Preparation on

blends of polyester with CEL preparation sequence is determined by the quality

and condition of the natural cellulosic fibre ratherthan the polyester component.

If the grey goods contain starch size or other

polymers not readily soluble or dispersible in water, itis necessary to extract or solubilise thesecontaminants before scouring.

Even with the water-soluble size polymers it is oftenadvisable to carry out an enzyme desizing process,because they may become difficult to solubilise afterdrying at temperatures above 100C.


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Influence of preparation on

disperse dyes Disperse dyes are particularly sensitive to the influence of

surfactants and polyelectrolytes, as regards both the quality andstability of the dispersion and the response of the dyes inexhaust dyeing systems.

The dyeing of polyester at a temperature in the range 120 to135C in circulating-liquor machines places severe demands on

initial dispersion quality and subsequent stability under adverseconditions.

The problem in the inherent instability of all dye dispersions,there being an overall tendency of fine particles to adhere

together with formation of larger particles. It is this limitedsolubility that favours growth of particle size. The solubility of disperse dyes normally increases with

temperature and dispersing agent concentration, although theseeffects vary greatly from agent to agent and from dye to dye.


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Alkaline Pretreatment

Controlled alkaline hydrolysis of the surfacelayer of the fibres confers a limited degree ofsilk-like softness to conventional

poly(ethylene terephthalate) materials. The resultant loss in mass is accompanied by

an increase in surface polarity arising from

the additional hydroxy and carboxyl groupsformed by ester hydrolysis.


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Influence of heat setting

temperatureInfluence of heat setting temperature on subsequentuptake of CI Disperse Red 1 by a polyester filament fabric


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Oligomer

: Cyclic tris(ethylene terephthalate)

Commercial samples of polyester fibres typically containbetween 1.5 and 3 .5% of the cyclic trimer


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Variation of aqueous solubility

of oligomerVariation of aqueous solubility of cyclic tris(ethylene terephthalate)crystals with temperature

Cyclic tris(ethylene terephthalate) is a crystalline solid that melts at 314 to 319C.Although it can be hydrolysed by strongly alkaline solutions, the reaction is very

slow because the cyclic trimer is almost insoluble in aqueous media


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Sizing agents for different

substrates


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Degree of removal of residual

sizing agent


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Rapid scour-dye process for

polyester


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Weight reduction of polyester Controlled alkaline hydrolysis of the surface layer of

the fibres confers a limited degree of silk-likesoftness to conventional poly(ethylene terephthalate)materials.

The resultant loss in mass is accompanied by anincrease in surface polarity arising from the additionalhydroxy and carboxyl groups formed by esterhydrolysis.

additions of ethylenediamine to accelerate thehydrolysis by caustic alkali was examined in a rapidprocess for only 1 to 5 minutes at the boil.

Prov ide more hydrophilicity of polyester


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Nylon Fibres

A heat setting treatment prior to dyeingnormally prevents

Differences in the degree of swelling of

nylon fibres arising from the uneven absorption of moisture

localised drying out of moist goods

It can result in unlevel shading faults


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Whitening of nylon

Reductive bleaching with sodium dithioniteunder acidic or neutral conditions

Oxidative bleaching with alkaline hydrogenperoxide, or with peracetic acid or sodiumchlorite under acidic conditions

Fluorescent brightening agents either aloneor in the presence of a reducing agent


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Why do nylon prefer reductive

bleaching? Oxidative bleaching treatments are the most effective

in overcoming the yellowness of grey-set nylon butanalysis reveals that some amino end-groups areoxidised and dye substantivity is lowered.

This effect significantly impairs the resistance of thenylon to photodegradation and lowers the lightfastness of dyeings and prints produced on thebleached substrate.

The more drastic the oxidative bleaching treatment,the greater the sensitivity of the treated nylon tophotodegradation.

In most instances nylon is bleached under reducing

conditions using sodium dithionite and a suitablefluorescent brightener under acidic conditions at pH 4to 5.


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Photodegradation of nylon

When nylon be in simultaneous contactwith light, heat, air, water vapour,ozone and gas fumes. Can we solve

with UV absorber ?

Or..

All these factors can catalyse or modify the fibre degradation reaction.


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Factors that enhance the resistance

of nylon to photodegradation (1)

Optimal purity of starting materials forpolymerisation

Minimal temperature of polymerisation, with

exclusion of oxygen Inclusion of protective inorganic salts,

particularly those of transition metals such asmanganese (II)

Inclusion of protective organic compounds asantioxidants


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Exclusion of fluorescent brighteners from thepolymer

Increased average molecular mass of the

polymer Increased content of amino end-groups, as in

deep-dye nylon variants

Minimal temperature of the polymer melt,with exclusion of oxygen


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Minimal concentration of delustrant, using theoptimal grade of titanium dioxide

Selection of suitable spinning lubricants Draw ratio as high as possible to ensure

maximum crystallinity, consistent with other

commercial requirements Storage of grey fabric away from direct

sunlight and away from heating systems


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Minimal temperature of heat setting in the grey state,consistent with the attainment of adequate set

Treatment in a stenter designed for steam injection

Alkaline rather than neutral or acidic conditions ofscouring

Oxidative bleaching should be avoided, butfluorescent brighteners can be applied underreducing conditions


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Dyes of high fastness to light (6-7) are preferred,with particular care in selecting suitable trichromaticcombinations

Certain metal-complex and milling acid dyes exert aprotective effect on nylon, whereas others maycatalyse photodegradation [15]

Preferable to dye at or near pH 5, since more

strongly acidic conditions can adversely affectantioxidants Inclusion of thiourea or hydroxylamine in the dyebath

eliminates dissolved oxygen and minimises the risk of

degradation in high-temperature dyeing

35048298 textile pre treatment right first time

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