Bleaching of wool and process recipe:
Wool is a type of animal fiber, which can be bleached by oxidizing agent hydrogen peroxide. Wool bleaching cannot be done by sodium or calcium hypochlorite, as it damages the fiber. On the other hand, bleaching can be done by reducing bleaching agents like sulfur dioxide.
Wool bleaching by sulfur dioxide:
In this method, the wool is bleached by the reducing agent sulfur dioxide. Bleaching is done by soaking wet wool in sulfur smoke or steam. In this method, a closed chamber is used for bleaching. The name of this chamber is a stove. It has to be made of wood, brick, or stone. Inside the stove are some vertical poles in the shape of a roll. Wool is hung on these poles. In one corner of the stove is an iron tray to hold sulfur.
Sulfur is ignited when a piece of reddish hot iron is placed in a tray. This results in bumps of sulfur which absorb the wet wool fibers resulting in wool bleaching. Note that the wool used must have a certain amount of moisture. If the moisture is low, wool does not absorb sulfur dioxide and if it is excessive, there will be uneven bleaching. At the end of bleaching, the wool is washed first with cold water and then with 0.5% hydrogen peroxide, and finally with water.
Wool Bleaching with Hydrogen Peroxide:
Bleaching wool by oxidizing agent hydrogen peroxide is very similar to cotton bleaching. However, the temperature and pH are kept low here. Bleaching is done by dipping the wool in the liqueur of the bleaching pot i.e. by steeping method.
The bleaching pot must be made of stainless steel, wood, stone, or concrete but cannot be made of copper or iron. This is because they act as agents to break down hydrogen peroxide.
Bleaching of wool and process recipe-Recipe:
Tetrasodium pyroPhosphate → 2 pounds
Ethylenediaminetetraacetic acid (EDTA) (30%) → 1 pound
Hydrogen peroxide (35%) → 2.5 gallons.
Or hydrogen peroxide (50%) → 1 gallon
The rest of the water is taken to make 100 gallons of solution. The wool is immersed in the solution and soaked directly at a temperature of 50°C to 55°C. However, wool should always be immersed in liqueur.
Again when the machine is bleached all the liqueurs are stirred at a temperature of 50°C for 3 to 5 hours. Here the pH of the solution has to be kept between7.5 to 9.
At the end of bleaching, the wool is smeared with 1% to 2% sodium bisulfite solution at room temperature for 10 to 20 minutes. Then it dries.