The pre-treatment of pure cotton or polyester/cotton fabric is mainly to remove impurities on the cotton fiber, so that the fabric has good printing and dyeing processing performance. The conventional desizing, scouring, and bleaching processes are set up for different impurities. But in production, it is found that the above-mentioned processes are not specific. What is the situation? Let's take a look together!
At the same time as desizing, the oil and wax in the raw cotton component also begin to saponify, which has a certain scouring effect. In the scouring process, not only the oil, wax, pectin, ash, lignin, etc. in the cotton component are removed, the slurry is also further removed, and part of the pigment can be removed.
In the bleaching process, hydrogen peroxide can not only remove pigments, but also has a certain removal effect on residual pulp and some impurities.
In the conventional process, the caustic soda is used for desizing and scouring, while in the hydrogen peroxide bleaching process, the caustic soda is only used to adjust the pH value of the bleaching liquid.
Since alkali is an intensifier of hydrogen peroxide, if the alkali concentration is increased, hydrogen peroxide will decompose to generate H00-, and the reaction speed will increase, resulting in a large amount of reactive consumption of hydrogen peroxide. More importantly, the excessively intensified hydrogen peroxide promotes the formation of H00·radicals, which will damage the fibers to a certain extent.
In addition, heavy metal ions such as Fe2+, Cu2+, etc. inevitably exist in fabrics, water, equipment, etc. in production, which will also cause the rapid decomposition of hydrogen peroxide and cause chain reactions.
Therefore, in the one-bath method of annealing, boiling, and bleaching, the amount of hydrogen peroxide in the strong alkali bath must be strictly controlled, and the stabilizer must meet three functions:
①Stable perhydroxy anion (HOO-);
②Shield heavy metal ions;
③Suppress the mass production of peroxyl radicals (HOO·).
"In the conventional bleaching process (pH 10 ~ 11), hydrogen peroxide is activated by alkali, and HOO- is mainly formed.
At this time, the water glass shields heavy metal ions due to its polymer network structure, can adsorb Fe2+ and block HOO—, so that Fe2+ does not undergo catalytic reaction, and at the same time inhibits the formation and decomposition of H00·radicals. Water glass can also combine with Ca2+ and Mg2+ ions in the bleaching solution to form highly dispersed magnesium silicate and calcium silicate colloids, which are adsorbed on the surface of the catalyst to deactivate it, thereby playing a stabilizing effect.
If the water glass is bleached in soft water, not only does it have no stabilizing effect, but on the contrary, the increase in the pH value accelerates 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 a good stabilizing effect and a low price, it cannot meet the above functions in the one-bath method of strong alkali annealing, boiling and bleaching. Therefore, it is unreasonable to use only water glass as a stabilizer in the prescription. If water glass is mixed with magnesium sulfate and complexing agent in a certain proportion, it can be suitable for the one-bath method of annealing, boiling and bleaching.
In addition, the scouring agent and detergent used in the prescription must be alkali-resistant, have good permeability in the alkaline bath, have the effects of emulsification, washing, solubilization, and dispersion, and have a high cloud point. If these quality indicators reach Less than required, it will also have a certain impact on the effect of the one-bath method of annealing, boiling and bleaching. In short, just choose the appropriate hydrogen peroxide stabilizer, scouring agent, penetrating agent and control the process conditions to correctly solve the excessive alkali The relationship between, intensification, stability, etc., will definitely make the one-bath method of annealing, boiling, and bleaching achieve ideal effects.
In addition:
① Excessive amount of sodium silicate will result in more residual hydrogen peroxide, which will not give full play to the bleaching effect.
②Reduce the amount of water glass and increase chelating stabilizers.
③The concentration of caustic soda can be appropriately increased, and the reduction rate can be increased.
④ The steaming temperature can be increased to 105-110℃.
