The cotton can be bleached with peracetic acid at 30°C by adding 2,2'-bipyridinium and sodium dodecyl sulphonate to the bleaching solution. The optimum pH is 7. The ferrous ions in cotton absorb pyridine from the solution, forming a trichelate of the bispyridinium ferrous ion, which is associated with the cellulose molecule. The concentration of bis-pyridine must be high so that all become tri-chelates instead of single or double chelates in order to get the best bleaching effect and stabilize the peracetic acid.
The typical prescriptions for low-temperature bleaching of peracetic acid are: sodium tetraborate 25.5 mmol/L, hydrogen peroxide 36.7 mmol/L, acetic anhydride 34.4 mmol/L, 2,2′-bispyridone 0.640 mmol/L, dodecane Sodium sulfonate (SLS) 2.60 mmol/L.
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The typical prescriptions for low-temperature bleaching of peracetic acid are: sodium tetraborate 25.5 mmol/L, hydrogen peroxide 36.7 mmol/L, acetic anhydride 34.4 mmol/L, 2,2′-bispyridone 0.640 mmol/L, dodecane Sodium sulfonate (SLS) 2.60 mmol/L.
The rinse solution was prepared by adding 0.9 mL of hydrogen peroxide (50%) to 200 mL of 17.5 g/L sodium tetraborate solution. Add the required 1.0% sodium dodecyl sulphonate solution to approximately 50 mL of water, inject a 500 mL graduated cylinder, and add the required 2000 g/L 2,2'-bipyridine solution to the graduated cylinder. Then, the solution containing hydrogen peroxide and sodium tetraborate was added, and water was added to 400 mL. The solution was then poured into a 500 mL three-necked round-bottomed flask and shaken manually from time to time in a constant temperature bath to achieve uniform temperature.
Then, acetic anhydride (1.3 mL) was added to the solution, and the mixture was further stirred by hand for 5 minutes to completely oxidize acetic anhydride. Care must be taken to maximize the conversion of acetic anhydride to peracetic acid and to prevent the expendable decomposition of peracetic acid. In the production of peracetic acid using hydrogen peroxide and acetic anhydride, the number of moles of hydrogen peroxide should be slightly in excess of the number of moles of acetic anhydride to prevent the formation of diacyl peroxide because of the potential explosiveness of diacetyl peroxide.
After the formation of peracetic acid, the cotton fabric sample was placed in a bleaching liquid, and was manually agitated from time to time. After being bleached for 60 minutes, it was taken out thoroughly with tap water, dehydrated and air-dried.
In the bleaching process, the decomposition rate of peracetic acid was 5.7% at 20°C and 81% at 60°C. Therefore, since the stability of peracetic acid is reduced, the bleaching effect increased with increasing temperature is offset, so the maximum whiteness index is obtained at 50°C, but bleaching at 30°C results in a whiteness index of 73.04.
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