The bleaching product is not white enough. Should I add more hydrogen peroxide or caustic soda?

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 processing properties. Conventional desizing, scouring, Each bleaching process is designed for different impurities. However, it was discovered during production that the above process was not specific. What happened? Let’s take a look!

While desizing, the raw cotton component The oil, wax, etc. also begin 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 slurry 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, the hydrogen peroxide will decompose to generate H00-. At the same time, the reaction speed will increase, resulting in a large amount of reactive power consumption of the hydrogen peroxide. . What’s more important is that excessive intensification of hydrogen peroxide promotes the formation of H00·free radicals, which causes certain damage to fibers.

In addition, fabrics, water, equipment, etc. during production It is inevitable that the presence of heavy metal ions such as Fe2+, Cu2+, etc. will cause the hydrogen peroxide to violently split 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 meet Three functions:

　①Stabilize perhydroxyl anion (HOO-);

　②Shield heavy metal ions;

　③Inhibit the massive generation of perhydroxyl radicals (HOO·).

In the conventional bleaching process (pH10~22), 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 catalytically reacting, and inhibiting the formation and decomposition of H00·free radicals. Water glass can also interact with Ca2+ and Mg2+ ions in the bleaching liquid combine 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 there be no stabilizing effect, but on the contrary, the increase in pH value 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, water Although glass has good stabilizing effect, the price is low. It is cheap, but in the one-bath method of strong alkali removal, boiling and bleaching, water glass cannot meet the above functions, so it is unreasonable to use water glass alone as a stabilizer in the prescription. Mixing in a certain proportion can be used for the one-bath method of boiling, boiling and rinsing.

In addition, the scouring agents and detergents used in the prescription must be able to withstand alkali, have good permeability in alkali baths, have the functions of emulsifying, washing, solubilizing, dispersing, etc., and have a high cloud point. If These quality indicators cannot meet the requirements, which also affects the effectiveness of the one-bath method of removing, boiling and rinsing. The results will have a certain impact. In short, as long as the appropriate hydrogen peroxide stabilizer, scouring agent, penetrant, and process conditions are well controlled, and the relationship between excessiveness, intensification, and stability in strong alkali can be correctly solved, the reduction, boiling, and bleaching can be achieved. One-bath method achieves ideal results

Also:

　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.

③ The concentration of caustic soda can be appropriately increased and the rolling residue rate can be increased.

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　④Steaming temperature can be increased to 105-220℃