1 Problems with poor whiteness and hair effect
Poor whiteness includes impure and uneven whiteness and the wool effect cannot reach more than 8-10cm/30min. This is related to the quality of the knitted fabric. For example, if there is a lot of low-grade cotton, it is often difficult to achieve good whiteness and wool effect. Of course, the key The most important issues are process formulation and additive selection.
In process formulation:
① The amount of H202 and NaOH must be sufficient
H202: After pre-treatment, it not only plays the role of bleaching pigments, but also has the function of removing impurities (including removing cottonseed hulls). If the amount of H202 is insufficient (including decomposing too quickly), the whiteness cannot be guaranteed. NaOH not only provides the necessary ingredients for H202 bleaching Alkalinity (PH), and combined with the scouring agent, plays a great role in removing impurities. If the amount of NaOH is insufficient, the impurity removal will be poor. The gross effect cannot meet the requirements first, and of course the whiteness cannot meet the requirements, so the amount of H2O2 and NaOH It can be said to be the primary factor in ensuring whiteness and hair effect;
② Use high-quality scouring agents
The comprehensive effects of scouring agents such as cleaning, emulsification, dispersion, and penetration must be excellent to ensure the removal of impurities and ensure whiteness and wool effect. However, the quality of scouring agents on the market is uneven, so we must choose products with excellent comprehensive effects. Not only the penetration and solid content are measured, the penetration is only one aspect to consider;
③ Oxygen bleach stabilizer and chelating dispersant
These two additives are mainly used to improve water quality, adsorb and complex metal ions such as Fe3+ in the water, and prevent metal ions from catalyzing the rapid and ineffective decomposition of H202. If H202 decomposes quickly and ineffectively, its whiteness and gross effect will not be achieved. At the same time, it will cause brittleness and even holes in the fabric. Therefore, in order to achieve whiteness and wool effect, excellent varieties of oxygen bleaching stabilizers should be selected, and the decomposition rate of H202 should be mainly considered in the selection. The addition of chelating dispersant not only chelates iron, etc., but also chelates and disperses various impurities in the water, so that these impurities will no longer contaminate the fabric again and cause dark whiteness and graying. Therefore, chelating dispersant not only It is necessary to consider its chelating force for metal ions and its dispersing force;
④ Process conditions: It takes a certain amount of time and temperature for the additives to react with impurities. If the conditions are not met, the pigments and impurities will not be completely removed, and the whiteness and hair effect will not be achieved:
⑤ Washing: Washing after scouring and bleaching is very important. It is necessary to clean the removed impurities to ensure whiteness and wool effect.
2 The cottonseed hulls are not completely removed
The removal of cottonseed hulls mainly depends on the expansion and swelling of cottonseed hulls by NaOH under certain conditions, and then the cottonseed hulls are removed with a certain mechanical cleaning force. Incomplete removal is mainly caused by insufficient temperature and time, so there must be sufficient water at a certain temperature. It takes time to completely remove cottonseed husks. H202 and scouring agents can help to remove cottonseed husks. Therefore, a certain temperature and time must be provided in the pretreatment to ensure the removal of cottonseed husks. At the same time, NaHS03 or anthraquinone substances can be added to help Cottonseed Husk Removal.
3 Holes and brittle damage
In addition to singeing holes, scratches during processing, and original holes in the gray cloth, the main reason for holes and brittle damage is the presence of Fe3+, Cu2+ and other metal ions in the H202 bleaching bath or on the cloth surface. These metals Ion catalytic decomposition H202 decomposes rapidly, causing brittle fiber damage. If metal ions (such as rust, etc.) are too concentrated in one place, the fibers and yarns will become brittle and form holes. Therefore, for H202 bleaching, high-quality oxygen bleaching stabilizers and chelating dispersants must be selected to complex and adsorb on the fabric and in the bleaching bath. The metal ions in it prevent H202 from decomposing too quickly and causing holes or brittle damage. If mercerizing alkali is used for bleaching, it must be ensured that there are no impurities such as rust in the alkali.
Of course, alkali on the cloth surface (the alkali removal is not clean) or acid (the acid removal is not clean) will also cause brittle damage. At the same time, under high temperature and alkali conditions, the fabric will be brittle and damaged in the presence of air. This situation can be prevented by adding weak reducing agents such as NaHS03. In addition, moisture and mildew in fabrics are also one of the causes of brittleness and holes.
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