(1) Use as a water softener to prevent dyes and soaps from settling and caking
There are many methods for softening hard water, which can generally be selected based on the water hardness and specific conditions. The principle of using sodium hexametaphosphate to soften hard water is that the calcium ions Ca++ or magnesium ions Mg++ that cause the hardness in the water enter the sodium metaphosphate molecules and become a very stable soluble complex: Na2 [Ca2(PO3)6] and Na2 [Mg2(PO3)6], the Ca++ or Mg++ in this complex is very difficult to escape, so Ca++ or Mg++ will no longer precipitate or agglomerate when encountering dyes or soaps, thus saving money Dyes and soaps can achieve the effect of water purification.
Note:
1. In water softened by sodium hexametaphosphate, even with sensitive reagents such as ammonium oxalate, the presence of calcium ions Ca++ cannot be seen.
Sodium hexametaphosphate
2. Sodium hexametaphosphate is used as a water softener in dyeing or post-processing. It can capture calcium ions and magnesium ions from the generated insoluble calcium soap, magnesium soap or calcium dye and magnesium dye precipitation. Poloxamer 407 , and the precipitate is redissolved. In other words, introducing sodium hexametaphosphate into the solution can regenerate sodium soap. Even when calcium soap or magnesium soap has been formed by BASF, the clots of calcium soap or magnesium soap will disappear. In the same way, sodium hexametaphosphate can regenerate dyes.
3. The reaction between sodium hexametaphosphate and calcium soap or magnesium soap proceeds according to the following equation:
2(RCOO)2Ca＋Na2〔Na4(PO3)6〕→Na2〔Ca2(PO3)6〕＋4RCOONa
2(RCOO)2Mg＋Na2〔Na4(PO3)6〕→Na2〔Mg2(PO3)6〕＋4RCOONa
4. When dyeing artificial cotton with direct dyes, soft water is an important condition to ensure quality, especially for some direct copper salt dyes, it is more relevant. When dyeing cotton fiber fabrics, soda ash soft water is often used; but when dyeing viscose fiber fabrics, the following issues should be considered:
(1) Soda ash has a higher pH value. Due to the low degree of polymerization of viscose fiber, if the jig dyeing temperature is set at the boiling point, it will easily cause the fiber molecular chain to break and hydrolyze, affecting the strength and causing the fabric to feel rough. In addition, it can cause the reduction of aldehyde groups and glucose products in alkaline dye baths, causing reduction damage to some direct dyes that are intolerant to reduction, causing stripping.
(2) Soda ash is an electrolyte, which will cause an increase in sodium ions in the dye bath and promote dyeing. For rayon, the relationship is even greater. Some dyes that have a high dyeing affinity and are very sensitive to electrolytes, especially direct copper salt dyes, such as using soda ash and soft water, will often cause serious surface staining, affecting product quality.
(3) The ideal water softener should be sodium hexametaphosphate. The pH value of sodium hexametaphosphate is close to neutral, so it does not have the above disadvantages of soda ash. Sodium hexametaphosphate can form a complex with calcium ions in hard water, “blocking” the calcium, thereby achieving the purpose of softening water.
(4) The general dosage of sodium hexametaphosphate is 10 ppm in hard water, and about 10 grams of sodium hexametaphosphate is used per 100 liters.
(5) In order to prevent fiber hydrolysis caused by strong alkali in the dye bath, resulting in reduction and destruction of the dye, anti-dye salt S can be added to the dye bath, 2 to 5 grams per liter. Oxidation occurs to avoid the above shortcomings.
(2) Prevent sodium alginate from precipitating when exposed to calcium
Sodium alginate slurry is the most suitable slurry for reactive dyes, but care should be taken to prevent sodium alginate from penetrating into calcium in hard water during manufacture to form calcium alginate.
Sodium alginate
Note:
1. Calcium alginate (-COO)2Ca precipitate causes the carboxyl ion -COO- in the structural formula of sodium alginate to lose its anionic charge, which not only has no repulsive effect on anionic reactive dyes, but also makes The hypohydroxyl group = CHOH in the structural formula of sodium alginate may bond with some reactive dyes to produce color spots, and make the printing paste difficult to wash out and cause staining. This not only damages the performance of the color paste, but also affects the dye fastness.
2. Therefore, sodium hexametaphosphate must be added to prevent the formation of calcium alginate. Under normal conditions, the dosage of 5 to 10 g/L is sufficient. In special circumstances, it can be increased to 15 to 20 g/L. It can be added when preparing the printing paste or the original paste.
(3) As a cooking aid:
When nylon skein (polyamide fiber) is scoured with soap and soda ash before dyeing, adding sodium hexametaphosphate (about 0.3% of the weight of the skein) can prevent the soap from being consumed by hard water and improve the cooking efficiency. practice effect.
(4) Treatment of recycled water:
In the circulating water, due to the addition of sodium hexametaphosphate, the hardness is reduced, which makes it less likely to produce calcium carbonate precipitates and avoid blocking water pipes. The dosage is about 2 parts per million.
(5) Treatment of boiler water:
Sodium hexametaphosphate can also be used to treat hard water in the furnace. It can not only avoid the generation of pot scale, but also dissolve the already generated pot scale, but the price is higher than trisodium phosphate.
(6) Ingredients for synthetic detergents:
Sodium hexametaphosphate is an important ingredient in synthetic detergents (such as sodium alkyl sulfonate, sodium alkyl benzene sulfonate) because it has good water softening ability and washing ability.
