Bleaching of Okra with Sodium Chlorite

Bleaching of Okra Bast Fibre With Sodium Chlorite

For bleaching, about 1 gm dewaxed okra bast fibre dried at 105°C was treated with 0.7% sodium chlorite (NaClO2) solution buffered at pH 4. Required amount of sodium chlorite was dissolved in a known volume of water, and its pH, which was 10.6, was lowered to 4 by the gradual addition of 0.2N acetic acid. pH readings were taken with pH meter (Pocket). The pH meter was standardized with a buffer solution of known pH and was checked
with another buffer solution of known pH. A buffer mixture of pH 4 (acetic acid-sodium acetate) was prepared and added to the chlorite CH3COOH-CH3COONa buffer solution in the proportion of 1 ml of buffer solution for every 10 ml of chlorite solution, to ensure that pH remained at 4 throughout the progress of the reaction. This pH maintaining is necessary because many organic acids are liberated during bleaching and unless the mixture is buffered the pH of the medium would change. The bleaching process was carried out by digesting the fiber for about 2 h at 90-95°C. For each gram of the fiber 80 ml of the mixture was used. After bleaching the fibre was filtered over a sintered funnel and washed thoroughly with distilled water. It was then treated with 2% sodium metabisulphite solution for 15 min. The fiber-liquor ratio was 1:50. Again the fiber was filtered and washed thoroughly with distilled water. The bleached okra bast fibre on the sintered funnel was then dried and preserved in a desicator.