Question

How is bleaching of fabric done? Explain the different steps involved.

Answer 1

Explanation:

After scouring process bleaching is done for get white fabric. Bleaching is done for removing natural color which is inherent in the fiber. Bleaching is the second steps of pretreatment of textile materials as well as wet processing technology. ... Bleaching agent occur some damage to the textile materials

Bleaching is an important and essential step in pretreatment of Textiles. It helps 'whiten' the textile material by removing undesired inherent coloring components. Generally, the natural fibres and their blends comprise about 50 % of total textile substrates and are invariably bleached, while the regenerated and synthetic goods are given this treatment considering the specific requirement. Depending on the substrate, a number of chemicals and application methods are employed to achieve optimum bleaching effect, however, it is also imperative to remove and get rid of the excess and leftover bleaching agent from the textile goods before subsequent wet processing. In this article an attempt is made to review various bleaching chemicals used in textile industry and the methods of their removal and cleaning.

Natural vegetable fibers like cotton, linen, jute, etc. contain varying extent of pigments like Chlorophyll, Xanthophyll and Carotene. This imparts off-white, yellowish brown hue and depends on the area of cultivation, climatic conditions and varies from crop to crop. Similarly, the animal fibers like wool and silk too contain non protein impurities which impart characteristic color.

Need of Bleaching

Bleaching is the process of decolorization of raw textile material by removing inherent and or acquired coloring components from the fiber. It provides base whiteness to the textile material which could be further whitened with the help of optical brighteners or dyed | printed depending on the desired end use. Even in case of regenerated and synthetic fibers, bleaching step is incorporated for achieving full white or extra bright shades. Though, in case of material to be dyed with dark and dull shades bleaching step could be omitted.

Bleaching can be carried out at various stages of conversion of fiber to garment i.e. from fiber, yarn, hank, woven, knit, towel, sewn up garments, etc. on various types of machines by simple hand processing to sophisticated bleaching ranges and by different application processes from exhaust to continuous.

 HOPE THIS HELPS YOU,,,....

     ¶  THANK YOU    ¶

Answer 2

The bleaching of fabric is done by using bleaching powder. The different steps involved are the removal of greasy matter, dipping in bleaching powder solution, treatment with acid, treatment with antichlor and then cleaning with water.

Explanation:

• Fabric or textile is bleached by using bleaching powder. The process of bleaching involves various steps.
• The steps involved in the process are:

1. Removal of the greasy matter: At first, the fabric is dipped in dilute $NaOH$ solution to remove greasy matter and then it is washed with water.
2. Dipping in bleaching powder solution: The fabric is then dipped in the solution of bleaching powder and that covers the fabric.
3. Treatment with acid: Now, the fabric is passed through a tank containing dilute sulphuric acid or hydrochloric acid.
4. The reaction of bleaching powder with the acid produces hydrochloric acid and nascent oxygen that causes bleaching of the fabric.
5. Treatment with antichlor: It is now treated with antichlor like sodium bisulphate and sodium thiosulphate. It reacts with chlorine to convert it into chloride ion so that chlorine does not act as oxidising agent.
6. Washing with water: The fabric is finally washed with water to remove hydrochloric acid and salts.

#SPJ2