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EXHIBITION

How does bleaching powder bleach a fibre textile?

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[Abstract]:


Artificial fiber and natural fibers are essentially the same, easy to color like cotton, hemp, silk and wool, hence the brilliant colors of rayon and rayon.

However, the dyeing of synthetic fibers is quite different.

Only polyamide has similar molecules and proteins, and the dye is similar to silk and wool.

Dacron, polypropylene, chloroprene and so on are very difficult to dye, because they do not touch the dye, do not hook, mordant does not adhere to.

The dye had to be mixed into the material prior to the spinning, and the colored silk was ejected to give the fabric color.

Conversely, to whiten the cloth, bleach is used to destroy the dye molecules.

So do you know how bleaching powder works?

An experiment has been performed in which a bunch of red roses are pinned under a glass bell jar and a burning sulfur is sent inside.

After a while, the color of the rose faded.

This is the sulfur dioxide generated by burning sulfur and the water molecules in the rose to produce sulfurous acid, which has the reducibility and destroys the pigment of the rose.

White cloth, paper and straw hats are often bleached with sulfurous acid.

However, oxygen in the air slowly oxidizes back the reduced pigment, so that old white cloth, white paper and straw hats often turn yellow.

Reduction can destroy pigment and achieve bleaching;

Oxidation can also destroy pigments and achieve bleaching.

The main component of bleach is calcium hypochlorite, which dissolves in water and releases hypochlorite.

Hypochlorous acid has a strong oxidizing power.

The dye molecules are oxidized by it, turning them into colorless compounds, and the bleaching takes place.

When Scheele discovered chlorine in 1774, he discovered that chlorine water was a permanent bleaching agent for paper, vegetables and flowers.

In 1785, The French chemist Bertolay proposed the application of bleaching to production, and noticed that the solution of chlorine-lime water was thicker than chlorine-water, the bleaching power was stronger, and there was no harmful effect of chlorine escaping.

In 1789, The British chemist Lloyd Tenet dissolved chlorine in lime milk to make bleach.

Bleaching powder is still made by passing chlorine into lime, which contains a little less than 1% water, because extremely dry lime does not react with chlorine.

The reaction process of bleaching powder production is relatively complex, and the main reaction can be expressed as follows:

Cl2 Ca (OH) 2 + 2 = 3 Ca (ClO) 2 + CaCl2 · Ca (OH) 2 · H2O + H2O

In more advanced bleach, chlorination can be carried out according to the following chemical equation, and the reaction is relatively complete:

Cacl2 · Ca (OH) 2 · 2 H2O + 2 cl2 H2O + 8 = Ca (ClO) 2 + 3 cacl2 · 4 H2O

Bleach is a mixture whose active ingredient is Ca(ClO)2.

Commodity bleach often contains impurities such as Ca(OH)2, CaCl2, Ca(ClO2)2 and Cl2.

Calcium hypochlorite is very unstable (but more stable than hypochlorite) and reacts with water as follows:

Ca (ClO) 2 + 2 h2o Ca (OH) 2 + 2 = hclo

As alkalinity increased in the solution, the bleaching process proceeded slowly.

Ca(OH)2 must be removed in order to produce a bleaching effect in a short time, so industrial bleaching powder is used by adding a small amount of weak acid, such as acetic acid, or a small amount of dilute hydrochloric acid.

There is no need to add acid to household bleach, since carbon dioxide from the air ACTS as a weak acid when dissolved in water:

Ca(ClO)2+H2O+CO2 = CaCO3↓+2HClOCa(ClO)2+2H2O+2CO2 = Ca(HCO3)2+2HClO

Artificial fiber and natural fibers are essentially the same, easy to color like cotton, hemp, silk and wool, hence the brilliant colors of rayon and rayon.

However, the dyeing of synthetic fibers is quite different.

Only polyamide has similar molecules and proteins, and the dye is similar to silk and wool.

Dacron, polypropylene, chloroprene and so on are very difficult to dye, because they do not touch the dye, do not hook, mordant does not adhere to.

The dye had to be mixed into the material prior to the spinning, and the colored silk was ejected to give the fabric color.

Conversely, to whiten the cloth, bleach is used to destroy the dye molecules.

So do you know how bleaching powder works?

An experiment has been performed in which a bunch of red roses are pinned under a glass bell jar and a burning sulfur is sent inside.

After a while, the color of the rose faded.

This is the sulfur dioxide generated by burning sulfur and the water molecules in the rose to produce sulfurous acid, which has the reducibility and destroys the pigment of the rose.

White cloth, paper and straw hats are often bleached with sulfurous acid.

However, oxygen in the air slowly oxidizes back the reduced pigment, so that old white cloth, white paper and straw hats often turn yellow.

Reduction can destroy pigment and achieve bleaching;

Oxidation can also destroy pigments and achieve bleaching.

The main component of bleach is calcium hypochlorite, which dissolves in water and releases hypochlorite.

Hypochlorous acid has a strong oxidizing power.

The dye molecules are oxidized by it, turning them into colorless compounds, and the bleaching takes place.

When Scheele discovered chlorine in 1774, he discovered that chlorine water was a permanent bleaching agent for paper, vegetables and flowers.

In 1785, The French chemist Bertolay proposed the application of bleaching to production, and noticed that the solution of chlorine-lime water was thicker than chlorine-water, the bleaching power was stronger, and there was no harmful effect of chlorine escaping.

In 1789, The British chemist Lloyd Tenet dissolved chlorine in lime milk to make bleach.

Bleaching powder is still made by passing chlorine into lime, which contains a little less than 1% water, because extremely dry lime does not react with chlorine.

The reaction process of bleaching powder production is relatively complex, and the main reaction can be expressed as follows:

Cl2 Ca (OH) 2 + 2 = 3 Ca (ClO) 2 + CaCl2 · Ca (OH) 2 · H2O + H2O

In more advanced bleach, chlorination can be carried out according to the following chemical equation, and the reaction is relatively complete:

Cacl2 · Ca (OH) 2 · 2 H2O + 2 cl2 H2O + 8 = Ca (ClO) 2 + 3 cacl2 · 4 H2O

Bleach is a mixture whose active ingredient is Ca(ClO)2.

Commodity bleach often contains impurities such as Ca(OH)2, CaCl2, Ca(ClO2)2 and Cl2.

Calcium hypochlorite is very unstable (but more stable than hypochlorite) and reacts with water as follows:

Ca (ClO) 2 + 2 h2o Ca (OH) 2 + 2 = hclo

As alkalinity increased in the solution, the bleaching process proceeded slowly.

Ca(OH)2 must be removed in order to produce a bleaching effect in a short time, so industrial bleaching powder is used by adding a small amount of weak acid, such as acetic acid, or a small amount of dilute hydrochloric acid.

There is no need to add acid to household bleach, since carbon dioxide from the air ACTS as a weak acid when dissolved in water:

Ca(ClO)2+H2O+CO2 = CaCO3↓+2HClOCa(ClO)2+2H2O+2CO2 = Ca(HCO3)2+2HClO