The grey cloth used in the medium-thickness pure cotton bonding lining has the characteristics of compactness and thickness, low cotton grade, and a lot of impurities. In order to improve its performance to meet the requirements of subsequent processing, the grey cloth must be bleached. The traditional cloth cooking pot bleaching process needs to be carried out under the conditions of high alkali, high oxidant, and high temperature. Although the treatment effect is good, the process is time-consuming, energy-consuming, and large in sewage. However, hydrogen peroxide and sodium hypochlorite are used as oxidants for bleaching. The effect is not ideal. Chlorine dioxide, as the fourth-generation A1 environmentally friendly bleaching agent, can remove impurities and cotton seed hulls from cotton fibers without degrading the cellulose, does not affect the strength of the bleached fabric, and can greatly reduce the amount of organic halide in the wastewater. , The pollution to the environment is smaller, and the goal of cleaner production can be achieved. However, ordinary Chlorine dioxide solution has problems such as short release period, fast release rate, and unstable storage and transportation process.
The slow-release solid Chlorine dioxide (de-emerging agent) uses a porous network structure of polymer as a carrier, combined with sodium chlorite and activated acid, and slowly reacts inside the carrier to form ClO2 during bleaching. It has a longer release period, The advantages of good stability and controllable release rate can meet the requirements of low energy consumption, low pollution and good bleaching effect in the bleaching process. Some researchers have explored and discussed the effects of bleaching agent concentration, pH, bleaching time and surfactant concentration on bleaching effect.
The first is the influence of the concentration of the deburring agent on the bleaching effect. As shown in the figure below, the whiteness of cotton fabric increases with the increase of the amount of deburring agent. When the concentration is greater than 25g/L, the whiteness of cotton fabric remains basically unchanged. This is because the reaction between Chlorine dioxide and impurities is more likely to occur as the concentration of the de-emergent increases. When the concentration reaches a certain value, all the colored impurities that can react with it are removed, so the whiteness no longer increases.
The influence of the pH value of the bleaching solution on the bleaching effect is shown in the figure. It can be seen that the whiteness of cotton fabrics decreases with the increase of the pH value of the bleaching solution, and the bleaching effect drops greatly when the pH value is greater than 6. This is because as the pH increases, the oxidation capacity of Chlorine dioxide gradually decreases, and the ability to degrade lignin, pigments and other impurities in the fiber decreases; at the same time, when the bleach is alkaline, part of the Chlorine dioxide will react with OH- to form Chlorate without bleaching effect weakens the bleaching effect.
The effect of bleaching time on the bleaching effect is shown in the figure. Since it takes a certain time for Chlorine dioxide to react with colored groups, the reaction curve is similar to a general chemical reaction. It can be seen that the reaction is almost complete after 10 hours, and the whiteness remains basically unchanged.
The rational use of surfactants in the bleaching process is beneficial to enhance the infiltration capacity of the bleaching solution on the surface of cotton fabrics, promote the bleaching agent to penetrate into the cotton fabrics faster, and can also separate impurities from the cotton fibers and improve the bleaching effect. As shown in the figure below, when the surfactant concentration is in the range of 1~5 g/L, as the surfactant concentration increases, the bleaching effect will increase greatly. When the surfactant dosage is greater than 5g/L, the whiteness is basically constant. Therefore, a surfactant concentration of 5 g/L can achieve good results in actual use.
Comprehensive research shows that medium-thick cotton fabrics use slow-release solid chlorine dioxide as the oxidant. The bleaching effect under normal temperature and pressure conditions can meet the product standard requirements. The whiteness is high and the effect is stable. There is no yellowing phenomenon. It can be promoted. In the bleaching of heavy canvas fabrics, it replaces the traditional three-step pretreatment process of desizing, scouring and bleaching. It is a bleaching agent with broad application prospects.
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