The pre-treatment of pure cotton or polyester/cotton fabrics is mainly to remove impurities on cotton fibers so that the fabrics have good printing and dyeing performance. The conventional desizing, scouring, and bleaching processes are set up for different impurities. . However, it was discovered during production that the above process was not specific. What happened? Let’s take a look together!
While desizing, the grease and wax in the raw cotton component The quality also begins to saponify, which has a certain scouring effect. During the scouring process, not only the grease, wax, pectin, ash, lignin, etc. in the cotton component are removed, but the slurry is also further removed, and some pigments can be removed.
In the bleaching process, hydrogen peroxide can not only remove pigments, but also has a certain effect on residual pulp and some impurities.
In the conventional process, caustic soda is used for desizing and scouring, while in the hydrogen peroxide bleaching process, caustic soda is only used to adjust the pH value of the bleach.
Since alkali is an activator of hydrogen peroxide, if the alkali concentration is increased, hydrogen peroxide will decompose to generate H00-, and at the same time, the reaction speed will increase, resulting in a large amount of reactive power consumption of hydrogen peroxide. What’s more important is that excessive agitation of hydrogen peroxide promotes the formation of H00·free radicals, which causes certain damage to fibers.
In addition, heavy metal ions such as Fe2+, Cu2+, etc. are inevitably present in fabrics, water, and equipment during production, which will also cause the hydrogen peroxide to violently crack and decompose, causing a chain reaction. .
Therefore, in the one-bath method of boiling, boiling and rinsing, the amount of hydrogen peroxide in the strong alkali bath must be strictly controlled, and the stabilizer must satisfy three functions: ① Stabilize perhydroxyl groups anion (HOO-); ② shield heavy metal ions; ③ inhibit the large amount of perhydroxyl radicals (HOO·).
In the conventional bleaching process (pH10~11), hydrogen peroxide is stimulated by alkali and mainly forms HOO-.
At this time, water glass shields heavy metal ions due to its polymer network structure, can adsorb Fe2+ and block HOO—, preventing Fe2+ from catalytic reaction and inhibiting the generation of H00·free radicals. Formation and decomposition. Water glass can also combine with Ca2+ and Mg2+ ions in the bleaching liquid to form highly dispersed magnesium silicate and calcium silicate colloids, which are adsorbed on the surface of the catalyst, causing it to lose activity and thus play a stabilizing role.
If water glass is bleached in soft water, not only will it have no stabilizing effect, but on the contrary, the increase in pH will accelerate the decomposition of hydrogen peroxide. But when the Fe2+ content exceeds the adsorption capacity of water glass, the stabilizing effect will be weakened. For this reason, although water glass has good stabilizing effect and is cheap, it cannot meet the above functions in the one-bath method of strong alkali removal, boiling and bleaching. Therefore, it is unreasonable to use water glass alone as a stabilizer in the prescription. If water glass, magnesium sulfate and complexing agent are mixed in a certain proportion, it can be suitable for the one-bath method of boiling, boiling and bleaching.
In addition, the scouring agent and detergent used in the prescription must be able to withstand alkali, have good permeability in alkali baths, and must have emulsification, For washing, solubilizing, dispersing and other functions, the cloud point should be high. If these quality indicators do not meet the requirements, it will also have a certain impact on the effect of the one-bath method of reducing, boiling and rinsing. In short, as long as you choose the appropriate hydrogen peroxide stabilizer With scouring agents, penetrants, and good control of process conditions, and correct relationships between excess, intensification, and stability in strong alkali, the one-bath method of retreating, boiling, and rinsing can achieve the desired results.
In addition: ① Too much water glass is used, and more hydrogen peroxide remains, which fails to fully exert the bleaching effect. ② Reduce the amount of water glass and increase the chelating stabilizer. ③The concentration of caustic soda can be appropriately increased and the rolling residue rate can be increased. ④The steaming temperature can be increased to 105-110℃. </p
