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Cotton - Scouring and Bleaching - Pretreatment

Peroxide Bleaching

In order to understand the various parameters and variables involved in the textile processing, we should look deep into each and every aspect of processing that affects the quality of dyeing. Any business activity involves the following 4 M's and 1 E. viz., Man, Machine, Method, Money & Environment. If all the 4 M's are efficiently employed and the environment is also conducive, the business will be a great success. The first and foremost class of dye is from natural origins – like leaves, nuts and roots of some unique plants. In those days, dyeing was an art. The art of coloring the fabric started during very ancient days by many special innovative methods.

As water and its quality play a very important role in wet processing, let us have a brief look into the quality of water required for wet processing, with an emphasis on reactive dyeing. We get water from various sources, like river, ponds, shallow wells and deep bore wells. According to the source of water, it contains many dissolved and suspended impurities. The water from a running river, contains many dissolved salts (solids) like Sulphates, Chlorides, silicates, Carbonates and Bicarbonates of heavy earth metals like Calcium, Magnesium, Iron, Aluminums, Sodium etc. The ratio of these salts varies according to the source of water. The general requirements of the water used in textile processing are given below:

The water should be colorless, clear and free from suspended impurities.
Should not be hard and have the tendency to deposit, scale on fabric or on water supply structures.
It should be non-corrosive.
It should be free from metals such as iron, manganese, aluminums and copper
It should neither be too alkaline or acidic.

Color is normally an indication of the presence of suspended and dissolved salts that may affect the fiber/yarn/fabric. So it has to be removed from water prior use in processing, by a suitable de-coloration technique.
Turbidity or Suspended solids are due to a fine suspension of inorganic salts like (clay. silica, calcium carbonate) or organic finely divided vegetable matter like algae, micro-organism etc. This should also be removed using a suitable filtration technique.
Dissolved solids - in water treatment and analysis this term is called Total Dissolved Solids (TDS). The TDS reflects the presence of unwanted elements in dissolved form, which has to be removed using a suitable method. Good quality water should not have a TDS more than 150 ppm.
pH value – Water with a pH value of more than 7 is alkaline and one below 7 is acidic. Most of the textile processing treatments are dependent on pH values.
Hardness (Calcium and Magnesium) – the presence of Calcium and Magnesium salts in water is called hardness of water.

Temporary Hardness: The presence of bicarbonates of Calcium and Magnesium in water is called temporary hardness. When the water containing these salts are heated to boil, the soluble bicarbonate salts will become insoluble carbonates and precipitate and the hardness disappears.
Permanent Hardness: The presence of carbonates, sulphates and chlorides of Calcium and Magnesium are called permanent Hardness, as this hardness cannot be removed by simple heating.

Related topics of your interest:

Basic Requirements for Hydrogen Peroxide Bleaching

Water Hardness - How does it affects Textile Processing?

Determination of Water Hardness - How to Test details?

Industrial Water Softening Treatment - A detailed Ion Exchange Method

A simple pretreatment of cotton - Useful tips and recipes of Peroxide Bleaching

Bio-scouring - technique, tips and benefits

Assessment of Bleached Goods

Useful Links on Water