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Saponification reaction and emulsification reaction takes place during this time which will convert all the insoluble material to soluble form.

Then it is subjected for hot wash, cold wash with water and it is dried. The material is then steeped in the solution containing hydrogen peroxide, sodium silicate and sodium hydroxide at 40oc. The temperature of the solution is increased to oc and it is bleached for minutes. Mechanism of H2O2 Bleaching: In practice, normally oxidative bleaching is highly preferred for bleaching the textile substrates in industries.

Reductive bleaching is not adopted due to the inefficient performance on cotton substrates and few limitations. Hydrogen Peroxide bleaching is an oxidative bleaching process applied to all kind of textile substrates. H2O2 is stable under neutral pH and it can be modified according to the suitability of the reaction. The operating pH for cellulosic is between The dye bath is prepared by pasting the dyestuff with sodium carbonate and water.

The material is then steeped in the dye solution at 40oc. Then it is subjected in the cooling bath for obtaining better exhaustion and it is dried. The dye bath is prepared by pasting the dyestuff with Turkey red oil, sodium hydroxide, sodium hydro sulphite and water. The dye bath is heated for 15 minutes at 50oc for complete vatting. The material is then steeped in the dye solution. Sodium chloride is added in two portions and dyeing carried for 60 minutes at 60oc.

Then it is squeezed and subjected for air oxidation, soaping and washing with cold water and it is dried. Calculation: Initial weight of cotton sample material : x grams Percentage of dye 0. The material is worked in the blank bath for 15 minutes for the carrier gets uniformly absorbed. The well dispersed dye dispersed dye pasted with wetting agent and dispersing agent is then added and the temperature raised to boil within 30 minutes.

The pH of the bath is maintained at6. The dyeing is continued at boil for 2hours. The material after dyeing is raised and soaped at boil with 2 gpl soap and 2gpl caustic soda at C for half an hour to remove residual carrier.

This is important as its presence impairs the fastness to light of the dyed material and it causes irritation of the skin and gives unpleasant odour. Recipe for Cold brand Reactive dyes Weight of cotton sample material : x grams Percentage of dye : 0.

The dye bath is prepared by pasting the dyestuff with water. The material is then steeped in the dye solution at 40oc for cold brand reactive dye. Then sodium hydroxide is added in two portions and dyed for another 45 minutes. Then it is subjected for soap wash, cold wash with water and it is dried.

Calculation: Initial weight of cotton sample material : x grams Percentage of 0. The main disadvantage of this process is that it is a slower process and requires an enormous floor space for storing water impregnating cloth. At first sight the use of acid could appear to be dangerous, since conditions, which degrade starch, are those on which cellulose is also liable to be attacked.

But if the cloth impregnated with dilute mineral acid solution is exposed to the air during the storage period, localized drying due to evaporation cause increase in the concentration of acid at that portion and if the concentration is sufficiently high cellulose is hydrolysed. To avoid this, moistened jute cloth is placed over impregnated fabric. A subsequent washing after acid treatment completely removes the starch. Water and aqueous acid extract significant quantities of the impurities.

They not only degrade starch-based product but also offer the advantage of removing Ca and Mg salts from the cotton fabric. An outstanding feature of enzyme desizing is the specific nature of the enzyme action. Enzymes are biocatalysts; they differ from normal chemical catalysts because they are very specific in their action, are thermo-labile, have relatively low energies of activation and are usually active only over a narrow range of pH.

They are classified by the names of the substrate they decompose, e. Some properties of enzymes are as follow: 1 Enzymes are complex and high molecular weight protein molecules. Chemically enzymes are proteins of high molecular weight e. The different preparations are applied under different conditions. Desizing enzymes may be classified based on the source from which they are obtained as in fig.

For the Cl2 desizing, open width cloth is impregnated with water and squeezed at required percentage expression. The squeezed fabric is passed through a chamber, which is provided with a false bottom, through which Cl2 gas is passed. In this case Cl2 reacts with water present in the cloth producing nascent oxygen and this nascent oxygen attacks starch, there by solubilizing it. It is then washed and afterwards antichlor with HCl.

Sodium chlorite in the presence of ammonium sulphate gives good desizing efficiency. Sometimes pH of desizing bath may be adjusted between 4 - 4. Then it is washed and neutralized.

This has a powerful oxidising action on the starch. This is accompanied by the conversion of bromine dioxide into oxygen and bromine. Hydrolysis of this bromine produces more hypobromous acid and the nascent oxygen generated is responsible for the oxidation of starch. There are different methods of oxidation, but the most likely one is the breaking of most stable ether linkage of the glucose ring by sodium bromite.

As shown above by the oxidation the ether group converted to aldehyde and then further to carboxylic acid which lead to reduction in D. P of starch and convert to water soluble products. In another mode of oxidation of starch, the opening of the glucose ring by rupture of C2-C3 link takes place that lead to formation of a dialdehyde.

The dialdehyde formed is not soluble in water, but soluble in hot alkaline solution. Hence the sodium bromite treatment should be followed by a hot alkaline treatment with or without an intermediate rinsing operation. On the other hand sodium bromite treatment also reduces the natural impurities present in the material mainly oxidise the some of the natural colouring pigments present which lead to the reduction in the chemical requirement for bleaching. The general process with sodium bromite involve the padding with liquor contains, 0.

The long padding time is required for min. The pH is the most important factor in this case, the pH should be around 10, and below pH 9 the decomposition of bromite is rapid. While above pH 11 the oxidation of starch is very slow. Then after storage for desired treatment time fabric is washed and treated with hot sodium hydroxide solution to remove the converted starch completely. We can check the desizing efficiency both quantitatively as qualitatively.

The quantitative method to check the desizing efficiency is the weight loss. But after desizing the fabric still contains fats and waxes both natural as well as added , which adversely affect the absorbency of the fabric. Thus the main purpose of scouring cotton fabric is to remove the natural as well as added impurities of essentially of hydrophobic nature as completely as possible and leave the fabric in highly absorptive state without undergoing a significant chemical or physical damage.

The scouring process is done by boiling the fabric in an alkali solution. The main processes occur during scouring are: I. Saponification of oils present in the fibre. Waxes and unsaponifiable material is removed by emulsification of the same. Pectins are changed into their soluble salts of pectic acid. Mineral matters are dissolved. Proteins are hydrolysed into degradation soluble products.

Dirt or dust is removed and held in a stable suspension by the detergents present in the scouring bath. Vegetables oils, animal fats and mineral oils are not soluble in water. Thus when grey cotton fabric immersed into water, the oil present in cotton will not allow the water to spread on the fibres. These vegetable oils are glycerides of fatty acids like stearic acid, palmitic acid, and oleic acid.

When such oils are heated with NaOH the oil splits into its constituents fatty acids and glycerine, out of which glycerine is water soluble. The fatty acid again react with NaOH to form its sodium salt i.

Thus the saponification reaction converts the insoluble and water immiscible oil is converted to water-soluble products. The waxes present in the cotton as well as in size formulations cannot be removed by saponification.

Waxes are esters of high molecular weight fatty acids and alcohols. The waxes and lubricating oils are not converted into their soluble products. They are therefore removed by emulsification. The Pectin substances are present in the cotton in the form of insoluble salts of Calcium, Magnesium and Iron.

These bivalent metal salts are solubilized in alkaline solution. Pectic acid is a compound of high molecular weight containing carboxylic group for every 6 Carbon atom. It is insoluble in water but soluble in alkaline solution. The quantity of inorganic matters is in the range of 0.

Phosphorous present in the form of organic and inorganic compounds which are mostly soluble in hot water and which can become insoluble in the presence of alkali earth metals. Therefore use of hard water during scouring can precipitate alkali earth metal phosphate, which can get deposited on the surface of the fibre instead of getting eliminating from it. The scouring process requires use of soft water because the use of hard water would cause precipitation or insolubalizaion of soap.

It must be considered that cotton fibre contains Ca and Mg salts pectin salts which are freed during alkali treatment and can also contribute to the insolubility of soaps and at the same time remains attached to the fabric in the form of hydroxides. Thus they might disturb subsequent operations such as bleaching, dyeing and printing. It is therefore necessary to add sequestering agents chelating agents or metal complexing agents e.

Sequestering agents also help in the elimination of iron, which can give problems during subsequent bleaching with hydrogen peroxide. Cotton proteins consist of protoplasmic residues. Proteins are mainly concentrated in the primary wall. The known colour, which appears during scouring, could be due to the reaction between proteins and carbohydrates in the alkaline medium.

During scouring some dust, dirt and solid particles are loosened from the fabric. So to remove these particles and to keep this in suspension or dispersion form, detergents are added in scouring bath. A detergent is a good wetting agent. If the detergent is used in scouring bath another wetting agent need not be added to the scouring bath. Therefore, there are three components in a cotton scouring bath: caustic, to swell and dissolve the motes and to saponify oils and waxes, surfactant, to lower the bath's surface tension so it can wet-out the fabric faster and to emulsify oils and waxes and chelating agent, to form water dispersible complexes with heavy metals.

This will make the fabric in a super white form. This process of decolouration of natural pigments is called the bleaching. The process of bleaching gives a sparkling whiteness to the fabric and hence makes it suitable for further processing. Hydrogen Peroxide H2O2 solution 3. The cotton fiber do convoluted. The cross-sectional shape changes. In mercerizing 4Ts are important. The quality of luster will begin to be adversely affected.

As the temperature is increased the quality of luster is adversely affected but on lowering the temperature no improvement in the luster is obtained. If the material is allowed to shrink during mercerizing then quality of luster will be impaired on the other hand if the material is stretched more no improvement in luster is achieved.

In order to make up for the shortenings of the roller mercerizing machine, a clip stenter is used for post-mercerization treatment, in which a widthwise tension is applied then most alkali is showered off the fabric kept by through alkali removal and neutralization using an openwidth washing machine.

This method of mercerization running fabric through a number of rollers without the use of a clip stenter is also called roller mercerization. The machine has a number of stainless rollers, or stainless and rubber rollers of a relatively large diameter tiered zigzag in close content to each other inside a long trough with the lower tier designed to submerge in alkaline solution for mercerization. Slack mercerizing is done by exhaust. The fabric is slacked and treated with NaOH solution by this process of luster is obtained but absorption is increased.

They are more convoluted and contain less internal cellulose. It is their lack of internal structure that causes than to dye polar some dyes stuffs with exaggerate more important really is this specked appearance other minimize.

The dead cotton problem can only be minimized by mercerizing the fabric by swelling become bigger and rounder the immature fibres and giving tem a rounder shape and a greater reflectivity. The swelling action opens up the internal structure of the fiber and makes it easier for dye to gain access and the increased reflectivity enables.

The overall effect is that we no longer see than or at least not as. There are anionic FBAs for application to cellulose in the presence of added salt. Anionic types for application to nylon or wool in the presence of acid disperse types for application to polyester and so on. Most fluorescent brightening agent are applied to cellulosic fibre at temperature between oC in quantities varying from 0. In case of animal fibres quantities of FBAs ranging from 0.

Polyester is brightened by exhaustion either by high temperature method at oC or at boil in the presence of carrier. Most of FBAs can also be applied by pad thermosole method at temperature upto 90oC.

At temperature greater than this some brightness sublime. Fastness to washing is also only moderate only polyamide fibre there are selected product with light fastness of 4, on polyester 7 and for acrylontrile When Fluorescent Brightener on wool fade as a result of exposure to light a pronounced discolouration is frequently developed.

It has been suggested that this is caused by decomposition product of the fluorescent compound. FBA are no substitute for bleaching but they improve the white and also allow reduction in the amount of bleaching agent required. Thus diminishing the risk of degradation of protein. They are frequently applied after bleaching. Diaminostibene diasalphonic acid.

Fluorescent dyes re-emit the absorbed energy as light of longer wave length. An FBAs is a fluorescent chemical that absorb in the ultraviolet region of the spectrum and emit blue violet light. Typical FBAs absorb light with a maximum absorption as a wave length between and mm and emit light with a maximum emission between and mm. Open navigation menu. Close suggestions Search Search. User Settings. Skip carousel.

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