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Care And Maintenance Of Garments - Reducing bleaches

Reducing bleaches a) Sodium hydrosulphite b) Sodium bisulphate c) Sodium thio sulphate

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.



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.

 

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