Factors such as concentration, temperature, time, and pH value are the main conditions for chemical reactions. In the process of hydrogen peroxide bleaching, the relationship between these factors should be clarified in order to formulate a reasonable process. So what are the factors that affect hydrogen peroxide bleaching?
1. Concentration
The reasonable concentration specified for hydrogen peroxide bleaching should be based on the principle of achieving a certain degree of whiteness and removing cottonseed hulls and minimizing fiber damage. The practice has proved that the relationship between fabric whiteness and hydrogen peroxide concentration is not proportional. When the steaming process is used, the concentration can be controlled at 3-5g/L to achieve a certain whiteness requirement. No matter how high the concentration is, the whiteness does not increase much, and on the contrary, it is easy to damage the fiber. Therefore, the concentration of the steaming process is generally 3-5g/L, and the thin fabric should be appropriately lower. The specific determination should be based on the equipment used, the bleaching method, the thickness of the fabric, the desizing and scouring conditions, and the liquor ratio. In order to reduce the damage to the fiber as much as possible, the concentration should below. To obtain higher whiteness, measures should be taken in scouring.
2. Temperature
The temperature has a direct relationship with the decomposition rate of hydrogen peroxide. Under certain concentration and time conditions, the decomposition consumption of hydrogen peroxide on the fabric increases with the increase of temperature. Therefore, the bleaching effect of the fabric increases with the increase of the decomposition rate of hydrogen peroxide on the fabric. When the temperature reaches 90-100 ℃, hydrogen peroxide can decompose 90%, and the whiteness is better; but when the temperature is 60%, the decomposition rate is only about 50%.
3. Time
The determination of hydrogen peroxide bleaching time is related to temperature. If the cold bleaching method is used, it needs to be stacked at room temperature for about 10 hours, but the high temperature steaming bleaching time can be greatly shortened. From the measurement of hydrogen peroxide consumption rate, steaming for 15min has reached 70%, steaming for 45-60min, the consumption rate has reached 90%, and tends to balance. It can be seen that the steaming time of 45-60min is enough.
4. Alkaline agent
In conventional bleaching, the pH value of the bleaching liquid is 10.5~11, and the addition of water glass cannot meet the requirements. Therefore, an alkali agent should be added to adjust the pH value. The commonly used alkali agent is caustic soda, and the dosage is 1-2g/L. It is an activator, which can promote the decomposition of hydrogen peroxide so that hydrogen peroxide can generate hydrogen peroxide ions with a bleaching effect. When the pH value is 10.5~11, the hydrogen peroxide decomposes at a medium speed to achieve the purpose of bleaching. However, in the de-scouring-bleaching and one-bath short-process processes of de-scouring and bleaching, the amount of caustic soda is high. Caustic soda not only adjusts the pH value but also has the functions of desizing and scouring. This makes the bleaching bath very unstable and accelerates the decomposition of hydrogen peroxide, which not only wastes hydrogen peroxide but may also cause fiber degradation and fabric brittleness. In order to control the decomposition rate of hydrogen peroxide, as mentioned above, it is necessary to add a suitable stabilizer to decompose the hydrogen peroxide according to the process requirements, and to achieve a balance between decomposition and stabilization, which is the "controlled hydrogen peroxide bleaching process with the help of stabilizers." ”, using this process can not only achieve better fabric whiteness and impurity removal effect, but also will not cause greater damage to the fiber.
