Textile bleaching

The objective of bleaching is to remove the natural color for the following steps such as dyeing or printing or to achieve full white.

Not only the natural impurities will remain in the greige material, but also the add-ons that were made during its cultivation, growth and manufacture in the form of pesticides, fungicides, worm killers, sizes, lubricants, etc.

The removal of these natural coloring matters and add-ons during the previous state of manufacturing is called scouring and bleaching.

It consists of several compartments in which fabric moves from one side to another with the help of guide rollers and is treated with chemicals, heated, rinsed, and squeezed.

[8][9] Wood ash (potash, or impure potassium hydroxide) was an early form of soap, known to have been used in bleaching since at least 1AD.

[10][11] This process of washing cloth in a solution of ashes (lye) and left in the sun, known as Grassing, is one of the oldest methods of bleaching textile goods.

[16][15] Around 1756 an alternative to soured milk was proposed by the Scottish doctor, Francis Home using a weak solution of sulphuric acid.

[17] This was made commercially viable by John Roebuck's manufacture of sulphuric acid and reduced the soaking time to 12 – 24 hours.

A second law in 1721 prohibited the use and wear of all printed, painted, stained or dyed calicoes [21] which stimulated demand for linen and fustian.

Scouring removes the impurities such as waxes, pectins and makes the textile material hydrophilic or water absorbent.

When bleaching action carries out with oxygen, it removes the chromophoric sites and makes the cloths whiter.

After scouring and bleaching, optical brightening agents are applied to make the textile material appear a more brilliant white.