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Care And Maintenance Of Garments - Bleaching

On the basis of mode of action, bleaching agents can be classified into three groups as below. 1.Oxidizing bleaches, 2.Reducing bleaches, 3.Optical bleaches.

Care And Maintenance Of Garments

 

Introduction

 

A garment that is properly cared for may be expected to last considerably longer than one that is not cared for adequately. It will look better all through its wear-life.

 

Care includes three elements namely cleaning, refreshing and storage. Cleaning is usually a more technical and more involved process than storage or refreshing. Washing and dry cleaning are two major overall cleaning methods. Washing may be either hand or machine. For either process there are variations in the required water temperature, the nature of the detergent used, the use of bleach, the length of soaking and agitation time, the method of moisture removal and the method and amount of pressing required.

 

BLEACHING

 

Bleaching is a complex process of removing colouring or discoloured matter from fabrics and made white. In laundering, the only object in using bleach is to remove stains, which do not respond to normal washing processes. Bleaching should be carried out carefully on all fabrics. Bleaching agents are chemicals hence the correct rate and intensity of bleaching is essential so as to avoid damage to the fabric.

 

On the basis of mode of action, bleaching agents can be classified into three groups as below.

 

             Oxidizing bleaches

 

             Reducing bleaches

 

             Optical bleaches

 

 Oxidizing bleaches: These have oxygen as a chief component which is liberated and on contact with the stain, forms a colourless compound.

 

 Reducing bleaches: These remove the oxygen from certain kind of stains and so, reduce them to a colourless compound.

 

Amongst the oxidizing bleaches, the following may be mentioned:

 

            Sunlight with moisture, air and grass

 

            Sodium Hypochlorite

 

            Sodium perborate

 

            Hydrogen peroxide

 

            Potassium permanganate

 

1.a) Sunlight with Moisture, Air and Grass : This is the oldest, easiest, cheapest and perhaps the best method of bleaching cotton and linen, and of removing colouring matter which on contact with oxygen becomes colourless. The oxygen from the air and grass liberated by the sunlight and in conjunction with moisture is the active bleaching agent. The article, particularly the stained part, must be moistened with water and exposed to the sun preferably on grass or shrubs or plants until the colouring matter disappear after which the fabric must be removed immediately. Otherwise long exposure to the sun will weaken it.

 

Before bleaching with any of the oxidizing chemical, the metallic buttons and other similar parts if any, must be removed since their oxidation may cause black stains on the fabric.

 

1.b) Sodium Hypochlorite or Javelle Water : 1lb (480g) washing soda � lb chloride of lime, 1 quart boiling water 2 quarts cold water.

 

Method: Take a solution of washing soda and boiling water. Mix chloride of lime with cold water. Stand the mixture for sometime, so as to settle down. Decant the clear liquid and add it to the washing soda solution. This will give sodium hypochlorite and calcium carbonate which will precipitate. Allow the precipitate to settle and then strain off the clean liquid. This must be always stored in coloured bottles as it deteriorates in the light.

Use: Sodium hypochlorite is a strong bleaching agent and can be used on white cotton and linen. Dilute it with equal quantity of hot water and sponge the strained portion with it until the stain is removed. Rinse the fabric in the plain water to wash out any residual amount of bleach.

 

1.c) Sodium Perborate bleach : It is made by mixing solution of borax and caustic soda with hydrogen peroxide. When mixed with warm water, it gives off oxygen and also forms an alkaline solution of hydrogen peroxide, and is used in the preparation of soap powders.

 

Method: Dissolve one ounce (about 28g) of chemical in one gallon (about 4 litres) of water. For treating animal fibres, neutralize the solution with acetic acid and for bleaching action makes it slightly alkaline with ammonia.

 

Use: Make a solution of sodium perborate in the proportion of one tea spoon to 1 pint of boiling water. Sponge the stain with this solution, mostly used on white linen and cotton.

 

1.d) Hydrogen Peroxide : It is used as an antiseptic and a deodorant. It is a mild and useful agent. It must however be used with great care as it may cause serious injury to fabrics. The compound is available in the market as solution of different concentrations. The chemical is very unstable in air. Hence, to maintain the strength for longer, it must be stored in dark air tight bottles at low temperature. This bleach readily splits up into water and oxygen and so colouring matter is oxidized in its presence. This action takes place most rapidly with alkaline solution.

 

Use: It is a safe bleach on all fabrics and is used for whitening of wool and silk in addition to cotton and linen, which show yellowness due to repeated washings. It must never be allowed to dry in the fabric. The 10 volume strength can be used without dilution for white linen and cottons but for other fabrics, it should be diluted by adding six parts of cold water to one part of hydrogen peroxide. Little ammonia is then added to make the solution alkaline.

 

1.e) Potassium Permanganate Bleach : This bleach has a high content of oxygen which will combine with, so remove, certain obstinate stains. Eg., perspiration, marking ink and mildew. It can be used on animal as well as vegetable fabrics. A brown colour is left in the fabrics which can be removed by treating it with hydrogen peroxide or oxalic acid. Potassium permanganate is available in the form of crystals and can be easily stored in a bottle.

 

Method & Use: Make a solution of potassium permanganate in the proportion of one ounce (about 28g) of bleach with one gallon (about 4 litres) of water for cotton and linen fabrics. For animal fabrics the above solution is diluted 2 fold with water. The fabric is steeped in the bleach for few minutes, and then the excess bleach is rinsed out of fabric which has now stained with characteristic brown colour. The article is then dipped in one of the following solution until the brown stain due to bleach is removed.

 

       Sodium hydrosulphite

 

       Oxalic acid solution (28g in 4 litres of water) or

 

       2% hydrogen peroxide acidified with acetic acid (1 teaspoonful of vinegar for 500ml of bleach)

 

The fabric must be rinsed thoroughly in water after treatment with above chemical.

 

3. Reducing bleaches

 

a) Sodium hydrosulphite        

b) Sodium bisulphate

c) Sodium thio sulphate

3.a) Sodium Hydrosulphite : This is sold in powder form. When dissolved in water, it readily absorbs oxygen to form sodium metabisulphite. Further, sodium melabisulphite by absorbing oxygen forms sodium sulphite and sulphur dioxide. The sulphur dioxide gets oxidized to sulphuric acid and this gives out by hydrogen. Thus the removal of stain is brought about in two ways. First the powder takes away oxygen from the stain, thus breaking up the colouring matter and secondly, hydrogen given off by sulphuric acid, removes the broken up components of the colouring matter. It can be safely used for all kinds of fabrics with the precaution that the temperature of the solution is suited to the fabrics.

 

Application: For bleaching in solution, the fabrics are steeped for few minutes in solution of 1 to 4 teaspoonfuls of the chemical in 1 pint (about 500ml) of hot or boiling water. The concentration of solution varies according to the resistance of stain and the nature of fabric. The fabrics then should be rinsed thoroughly in water containing high concentration of soap.

 

Uses: The bleach can be used in spotting treatment for many stains due to grass, dung, boot polish, mildew, ink, potassium permanganate and dye stains.

 

The bleach can also be used for coloured clothes. In such cases, sometimes bleach may accidentally run into the colour to change it. Immediately dipping into an alkaline solution or immediate application of soap may rectify this problem.

 

Precautions: The bleach is sensitive to decomposition by moisture, heat and oxygen. Sometimes, it may catch fire. Therefore, it must be stored in air tight, moisture free containers. The bleaching work must be done in the open or near the window to let the released sulphur dioxide escape, which otherwise may cause irritation to throat and lungs.

 

Further care must be taken during use in avoiding the contact of bleach with metal parts, as it may cause black stain on all fabrics. Vessels of wood or earthenware only should be used.

 

3.b) Sodium bisulphite : This is very mild reducing agent and is obtained by the partial neutralization of 'sulphuric acid' with 'caustic soda'.

 

The bleaching effect of this chemical is due to release of sulphur dioxide which reduces the stain by removing oxygen, to discolour it.

 

Ingredients:                            Sodium bisulphite          - 2 tsp.

 

Water                   - 1 pint (about 500 ml)

 

The solution is obtained by mixing the two components.

 

Application: The stained part of fabric dipped in the bleach until the colour is removed. Therefore, it is thoroughly washed to remove residual chemical and air dried. The last step is essential as any residual sulphur dioxide may absorb atmospheric air to form sulphur trioxide which with water forms sulphuric acid.

 

3.c) Sodium thiosulphate : This chemical is also a reducing agent which acts through liberation of sulphur dioxide. For bleaching of cotton fabric, hyposolution is obtained by dissolving one ounce (about 28g) of sodium thiosulphate and � ounce of 36% acetic acid in 8 quarts (about 8 litres) of water. The fabrics are then treated as with sodium bisulphite bleach.


4. Optical bleaches

 

Optical bleaches are used for white fabrics. These are fluorescent white compounds not true bleaches. Eg. Tinopal . These compounds do not readily bleach but give a white effect. These fluorescent white compounds are absorbed by the fibre and exit a bluish appearance that covers up yellow things the fluorescent colourless dyes convert the invisible ultra-violet rays to visible light.

 

5. Over bleaching

 

The overbleaching of cotton and linen fabrics is one of the main cause of general weakness of the fabrics. The fibres become brittle and harsh and give a distinct 'crackle' when rubbed together.

 

To overcome this problem, following precautions should be used during all beaching operations:

 

         Use bleach of known strength.

 

           Keep temperature below 60�C

 

            Always measure quantity of bleach accurately, and

 

            Always dilute bleach and add gradually.

 

In most cases, over-bleaching is due to chlorine bleaches, but oxidizing agents do have the same effect on cotton and linen. Chlorine bleach should never be applied at temperature exceeding 160�F (71 o C).

 

6. Additional Reagents

 

In addition to soaps and other supplies, certain chemicals and materials are frequently used in laundries for specific purposes. These can be categorized under following groups:

 

a) Alkaline reagents     

b) Acidic reagents

c) Organic solvents, and        

d)Absorbents

 

a) Alkaline Reagents

 

(i) Ammonia (Ammonium Hydroxide or Liquor Ammonia): This is a strong alkali and is used for removing greasy stains and scorching on animal fabrics (Solution of 1 to 4 tsp in 500 ml of warm water is used); removing smell of Jevelle water; neutralization of remaining acids in fabrics.

 

However, this chemical causes yellowing of silk and wool, bleaching of colours and tendering of the fabrics, if concentrations, higher than recommended are used. Concentrated ammonia is highly volatile, release high amounts of ammonia gas which causes suffocation and a choking sensations due to its pungent smell. Therefore, either diluted ammonia solution be first prepared or household ammonia be purchased for use. In the period of non-use both concentrated as well as diluted ammonia solution should always be stored in refrigerator.

 

(ii) Washing Soda (Sodium Carbonate) : This is a most commonly used chemical in laundry work. It is marketed in crystal form which dissolves easily in boiling water. It is often used with soaps to improve their detergent power. The chemical is used for many other purposes such as softening of hard water, neutralization of acids, removal of acid stains from bleached cotton and linen fabrics and emulsification of grease. In addition to the above, washing soda is also used for removal of vegetable stains and, scorching. For this purpose one to four teaspoons of chemical is dissolved in about 500ml boiling water. The fabric is then treated with this solution when hot, for about 15 minutes and then rinsed in plain water.

 

Besides the above useful qualities, washing soda sometimes becomes undesirable as it causes yellowing of white fabrics. Further, it is also injurious to skin and hence care should be taken to avoid direct contact of hands, during washing of fabrics for long periods.

 

(iii) Borax (Sodium Tetraborate) : It is a mild alkaline chemical, soluble in cold water. It can be used on all the fibre types. In market, is is available as white crystal-line granules.

 

Uses: It is used to neutralize acids after stain removal.

 

It has a bleaching action on cotton and linen fabrics which are yellowed due to repeated washings. Such fabrics are whitened by boiling in solution of borax.

 

Presence of borax in starch prevents the 'scorching' or 'browning' of starch at high temperatures, used in finishing collars.

 

b) Acetic Reagents

 

(i) Acetic acid: The household form of acetic acid is vinegar (about 6% acetic acid). It is available in market in various strengths. Glacial acetic acid is the purest and strongest of all. The acid should not be used in metal vessels, but only in glass, plastic, enameled or earthenware vessels.

 

Uses: A weak solution of vinegar (2 teaspoonful in one litre water) is used as a steeping bath to remove over-bluing and as a neutralizing agent.

 

After washing the fabric, a final rinse in weak acetic acid solution, in addition to fixation of colour also gives an added brightness to the colours.

 

Rinsing in weak solution of acetic acid retains the original finish of the fabrics made from silk and rayon.

 

Acetic acid effectively substitutes stronger sulphuric acid used in dyeing of silk.

 

It helps in correction of finishing faults on cellulose acetate. If cellulose acetate fabrics are finished at too high a temperature, shiny glazed marks are produced on the fabric, which can be mistaken for grease marks. This defect can be removed by immersing the fabric in cold 20% acetic acid solution for about one hour, after which the article without water is wrapped in a cloth and the solution is extracted lightly. Then drying is carried out at about 140�F (60�C).

 

Precautions: Too much acetic acid may harm wool or silk as these fabrics have high affinity for acids. During subsequent washing, if excess acids not rinsed off, it will split a soap solution to give the fabric a greasy appearance, with a foul smell of fatty acids.

 

(ii) Oxalic acid: It is highly toxic and is marketed as white crystals. Use: It is used,

 

          To remove iron mould and fruit stain,

 

          To bleach the brown stain due to potassium permanganate,

 

          To remove tannin-base of writing ink, in combination with hydrogen peroxide, and

 

As a cleanser for white straw-hats.

For removing the stains, the article is soaked for about ten minutes in a hot solution of 1 to 4 teaspoonfuls of oxalic acid dissolved in about 500ml of water. It is then thoroughly washed. Then ammonia (100%) or borax is added to neutralize the excess acid.

 

Precautions : It must not be used on wool or silk as it causes permanent brown stains on such fabrics.

 

Care must be taken not to treat the article at too high a temperature (not over 140�F, 60�C) or with too strong a solution and chemical must not be allowed to dry in article, as any of the above may weaken the fabric.

 

Wooden spoons must be used for handling the chemical.

 

(iii) Oleic acid (Olein) : This belongs to class of fatty acids and forms soap when reacted with an alkali.

 

Uses: It is used for spotting of grease and oil stains. Oleic acid is applied to the stain and allowed to react for about 15 minutes or till the spot is dissolved. The part being treated is squeezed followed by dipping in weak solution of ammonia, which produces the soap. The stain is then rubbed or brushed until it is removed by the lather.

 

This acid is used to treat cotton and linen. It readily melts wool, tends to discolour silk and is unsuitable for coloured fabrics. It must always be rinsed well from the fabrics, otherwise a rancid odour will develop.

 

c) Organic Solvents:

 

Specific organic solvents can be applied to most of the fabrics either to remove stains or to 'Dry clean'. They do not harm the fibre or their colour. However, because of high cost, these are not used at home. Some of the most important solvents used in laundries are described below:

 

(i) Cleaning benzene (Petrol) : This is obtained by distillation of petroleum and is highly inflammable. It should never be stored in large quantities indoor or be used near fire.

 

Use: It is used for spotting of grease stains and dry-cleaning.

 

(ii) Carbon tetra-chloride : It has action similar to that of petrol, but is more expensive. However, it has the advantage of being non-inflammable, but is highly toxic. Therefore, it should be worked with either in open or near open window, as it is extremely volatile.

 

Uses: It is solvent which can be used on all fabrics for removal of paint and grease stains.

 

(iii) Acetone : It is very useful solvent for treating many stains. However, it is highly inflammable and also cannot be used for cellulose acetate rayon which is rapidly dissolved in this solvent.

 

Uses: On fibres, other than cellulose acetate and vinyon, acetone can be effectively applied to remove stains due to paint, nail polish, lipstick, varnish and shoe polish etc.

 

(iv) Methylated spirit (alcohol) : It is alcohol which is artificially coloured and toxified by addition of methyl alcohol, to make it unsafe to drink.

 

Uses: It is used for removing sealing wax, silver nitrate and other silver stains, but it is not a very effective solvent for organic stains. Its usefulness increases when employed along with soap. Alcohol dissolves acetate rayon, but can be used safely on all other fabrics.

(v) Parrafin : This is wax which is a by-product of petroleum refineries.

 

Uses: It is used in removing grease and paint stains on rubber fittings in laundry appliance.

 

(vi) Turpentine : This is more expensive than paraffin and possesses a distinctive smell. It is inflammable and volatile.

 

Uses: It is used to destain the fabric spots due to grease, paint, varnish and printer's ink. It can be safely used on all fabrics including acetate and nylon.

 

d) Absorbents

 

Several absorbents are used in home and in laundries for removal of grease spots from all fabrics as well as for general treatment of light coloured fabrics that are evenly soiled. These can also be used for articles like, furs, and dark coloured gloves which cannot be cleaned by solvents alone. Examples are French chalk, common-salt, bran, fuller's earth, bread-crumbs, powdered magnesia and other commercial dry-cleaning powders.

 

Application: To remove the stain or in general cleaning, first of all, brush off the loose dirt from the article and then spread absorbent. Rub it lightly in a circular motion and let it remain for half an hour. Then shake the powder and brush the whole garment.

 

Bran, moong power and bread-crumbs are used after light warming. They are useful for cleaning dark-coloured felts, furs, camel-hair cloth and greasy soiled sarees.

 

Use: The absorbents are used for cleaning grease marks on both light and dark coloured fabric of all kinds, white laces, fur, coats, shawls and felt hats. These do not harm the fabrics in any way.

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