The reason why most of the shell remains and the whiteness is not enough and how to solve it!

The pretreatment of pure cotton or polyester/cotton fabrics is mainly to remove impurities from cotton fibers, so that the fabrics have good dyeing and printing performance. Conventional desizing, scouring and bleaching processes are set for different impurities. But in production, the above process is not specific. What is the situation? Let's have a look together!
While desizing, the oils and waxes of raw cotton components also begin to saponification. In the scouring process, not only oil, wax, pectin, ash and lignin in cotton components are removed, but also pulp is further removed, and some pigments can be removed. In the bleaching process, hydrogen peroxide can not only remove pigments, but also remove residual pulp and some impurities. In the conventional process, caustic soda is used as desizing and scouring, while in the hydrogen peroxide bleaching process, caustic soda is only used to adjust the pH value of the bleach. As alkali is the activator of hydrogen peroxide, if the concentration of alkali is increased, the hydrogen peroxide will be decomposed into H00-while the reactive power of hydrogen peroxide will be consumed due to the faster reaction speed. More importantly, the excessive intensification of hydrogen peroxide promotes the formation of H00 & middot, and the formation of free radicals has certain damage to the fibers.
In addition, in the production of fabrics, water, equipment and other unavoidable presence of heavy metal ions such as Fe2+, Cu2+, will also cause hydrogen peroxide decomposition, causing chain reaction. Therefore, in the desizing, boiling and bleaching one-bath process, the dosage of hydrogen peroxide in strong alkali bath should be strictly controlled, and its stabilizer must satisfy three functions:
(1) stable over Hydroxyl Anion (HOO-);
Shielding heavy metal ions;
(3) inhibit the mass production of hydroxyl radical (HOO·).
In the conventional bleaching process (pHl0 ~ 11), hydrogen peroxide is mainly activated by alkali and mainly forms HOO-.
At this time, water glass can absorb Fe2 + and block HOO&mdash because of its polymer network structure shielding heavy metal ions, so that Fe2+ does not occur catalytic reaction, while inhibiting the formation and decomposition of H00· free radicals. Water glass can also combine with Ca2+ and Mg2+ ions in the bleaching solution to form highly dispersed magnesium silicate and calcium silicate colloid, which can be adsorbed on the surface of the catalyst and make it inactive, thus playing a stabilizing role. If sodium silicate is bleached in soft water, it will accelerate the decomposition of hydrogen peroxide instead of stabilizing it. But when the Fe2+ content exceeds the adsorption capacity of sodium silicate, it will weaken the stabilization effect. For this reason, although sodium silicate has good stabilization effect and low price, it can not meet the above functions in one bath method of strong alkali desizing, boiling and bleaching. Therefore, it is unreasonable to use single water glass as stabilizer in the prescription. If sodium silicate, magnesium sulfate and complexing agent are mixed in a certain proportion, it is suitable for one bath method of desizing, boiling and bleaching.
In addition, the scouring agent and detergent used in the prescription must be alkali-resistant, have good permeability in the alkali bath, have emulsifying, washing, solubilizing, dispersing and other functions, and have high cloud point. If these quality indicators do not meet the requirements, they will also have a certain impact on the effect of desizing, boiling and bleaching one-bath method. In a word, as long as the selection is made. Choosing proper hydrogen peroxide stabilizer and scouring agent, penetrating agent and controlling process conditions, correctly solving the relationship between excessive, intensification and stability in strong alkali, will surely make the one-bath method of desizing, boiling and bleaching achieve ideal effect.
In addition, excessive amount of sodium silicate and more residual hydrogen peroxide failed to give full play to the bleaching effect.
2. Reduce the consumption of sodium silicate and increase chelating stabilizer.
3. The concentration of caustic soda can be raised appropriately and the rate of rolling up can be increased.
4. The steaming temperature can be increased to 105— 110 C.