Cotton bleaching process by sodium chlorite:
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Dr. G. P. Vincent discovered sodium chlorite in 1939 as an oxidizing bleaching agent. He was speaking at the annual meeting of the American Association of Textile Chemists and Colorists (AATCC). Fabrics bleached by sodium chlorite are very well white. Because in this case there is no possibility of damage to the fabric by over bleaching.
Cotton bleaching process by sodium chlorite-Bleaching method:
Even using different grades of cotton, the white color of very good nature is available. Sodium chlorite is done in a bleaching acid medium. That means bleaching pH is kept from 3.6 to 4.2. Here sodium acetate and sodium hydrogen phosphate are used as buffers.
Chloric acid in sodium chlorite bleaching was thought to be responsible for bleaching. But now we know that it has changed. Chlorine dioxide (CIO) is responsible for bleaching. Sodium chlorite is used for bleaching cotton and in most cases for bleaching cotton or cellulose fibers.
Cotton bleaching process by sodium chlorite-Bleaching recipe:
Sodium hydrogen phosphate → 0.25 – 0.5% (percentage of fabric weight)
Weighting agent → 0.10 -0.25% (percentage of fabric weight)
pH → 8
Good results are obtained here as sodium dihydrogen acts as a phosphate buffer. Moreover, it has a special role in whitening. The mentioned chemicals are dissolved in separate containers and then taken to Kier. Here the pH of the solution is maintained at 3.8 to 4.2 using formic acid. The liqueur is circulated in cold for 15 to 20 minutes. The temperature is then raised to 80°C to 85°C and the bleaching is continued for 2 to 3 hours. The cloth is then washed and dried.
Continuous bleaching method:
Bleaching can be done by sodium chlorite with the help of J-box in a continuous method. To bleach continuously with sodium chlorite, the padding is first dipped in manganese and soaked in the bleaching solution. Based on the color and quality of the fabric, the amount of chlorite, buffer, acid, and wetting agent is given in the impression solution. The cloth is then kept in a J-box at a temperature of 85°C to 90°C for 2 to 6 hours.
Sodium Chlorite (60%) → 1% (Percentage by Fabric Weight)
Sodium carbonate → 0.5-1% (percentage of fabric weight)
Formaldehyde → 0.2 – 1% (percentage of fabric weight)
Wetting agent → 1% (percentage of fabric weight)
The percentage of ingredients is taken based on the weight of the fabric. After squeezing, the rolls are made and covered with polythene sheets.