35048298 textile pre treatment right first time
TRANSCRIPT
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
1/53
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
2/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
3/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
4/53
Troubleshoot in pretreatment
:Factor to yellowing of textiles
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
5/53
Water Specification for textile
wet processing
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
6/53
Average water consumption
by fibre type
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
7/53
Water consumption by process
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
8/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
9/53
Composition by mass of a
typical cotton fibre
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
10/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
11/53
Sizing agents for different
substrates
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
12/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
13/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
14/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
15/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
16/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
17/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
18/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
19/53
Advantages/disadvantages of
bleaching with hypochlorite
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
20/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
21/53
Advantages/disadvantages of
bleaching with chlorite
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
22/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
23/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
24/53
Advantages/disadvantages of
bleaching with hydrogen peroxide
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
25/53
AOX values for cotton bleached
with various oxidising agents
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
26/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
27/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
28/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
29/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
30/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
31/53
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%
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
32/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
33/53
Traditional process sequence
for polyester fabrics
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
34/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
35/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
36/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
37/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
38/53
Influence of heat setting
temperatureInfluence of heat setting temperature on subsequentuptake of CI Disperse Red 1 by a polyester filament fabric
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
39/53
Oligomer
: Cyclic tris(ethylene terephthalate)
Commercial samples of polyester fibres typically containbetween 1.5 and 3 .5% of the cyclic trimer
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
40/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
41/53
Sizing agents for different
substrates
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
42/53
Degree of removal of residual
sizing agent
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
43/53
Rapid scour-dye process for
polyester
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
44/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
45/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
46/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
47/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
48/53
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.
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
49/53
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
50/53
Factors that enhance the resistance
of nylon to photodegradation (2)
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
51/53
Factors that enhance the resistance
of nylon to photodegradation (3)
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
52/53
Factors that enhance the resistance
of nylon to photodegradation (4)
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
-
8/4/2019 35048298 Textile Pre Treatment Right First Time
53/53
Factors that enhance the resistance
of nylon to photodegradation (5)
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