What is Textile Bleaching? Different types of textile bleaching with advantages-disadvantages.

Introduction

Bleach is the common name for any chemical product that is biologically local and used to clean and remove stains at home. This often refers specifically to a dilute solution of sodium hypochlorite, also called liquid bleach.

Many bleaches have broad-spectrum bactericidal properties that make them useful for disinfecting and disinfecting germs and are used in swimming pool sanitation to control bacteria, viruses, and algae and in many places where disinfection is required. They are also used in many industrial processes, especially in the bleaching of wood pulp. Bleaches have other minor uses such as removing weeds, weeding, and increasing the longevity of cut flowers.

Bleaching powder

What is Textile Bleaching? 

Textile bleaching is one of the steps in making textiles. All raw textile materials, when they are in natural form are known as ‘grease’ materials. This grease material will have natural color, odor, and impurities that are not suitable for clothing materials. Grease ingredients contain not only natural impurities but also add-ons made in the form of pesticides, fungicides, worm killers, sizes, lubricants, etc. during its cultivation, growth, and production. Bleaches work by reacting with many colored organic compounds like natural pigments and converting them into colorless dyes. Most bleaches are oxidizing agents, and some are reducing agents.

Type of textile bleaching

These are three types-

A. Chlorine, a powerful oxidizer, is an active agent in many household bleaches. Since pure chlorine is a toxic corrosive gas, these products usually contain hypochlorite that releases chlorine when needed. Bleaching powder usually means a composition containing calcium hypochlorite. Examples- are sodium hypochlorite and sodium chlorite.

B. Bleaching agents that do not contain chlorine are generally made based on peroxides like hydrogen peroxide, sodium percarbonate, and sodium perborate. These bleaches are called 'non-chlorine bleach', 'oxygen bleach', or 'color-safe bleach'.

C. There are niche uses for bleach reduction, such as sulfur dioxide used to bleach wool, either as a gas or from a solution of sodium dithionite and sodium borohydride.

Bleaches usually react with many organic substances in addition to stimulant pigments, so they can weaken or damage natural materials such as fibers, fabrics, and leather, and intentionally apply dyes such as denim blue to blue. For the same reason, eating products, breathing in smoke, or contact with skin or eyes can be harmful to health.

Chemical reaction

Sodium hydrosulfite is one of the most important reductive bleaching agents. It is a white crystalline powder with a weak sulfurous odor. It can be obtained by reacting sodium bisulfite with zinc.

2 NaHSO₃ + Zn → Na₂S₂O₄ + Zn (OH) ₂

It is used in many industrial dyeing processes to remove excess dyeing, residual oxides, and unsightly pigments and to bleach wood pulp.

The reaction of sodium dithionite with formaldehyde produces Rongalite,

Na₂S₂O₄ + 2 CH₂O + H₂O → NaHOCH₂SO₃ + NaHOCH₂SO₂

Which is used in bleaching wood pulp, cotton, wool, leather, and clay?

Form of bleaching

Bleaching powder, is usually, a mixture of calcium hypochlorite Ca (ClO) ₂, calcium hydroxide Ca (OH) ₂, and calcium chloride (CaCl₂) invariable amounts. Sold as a white powder or in tablets. It is used in many of the same applications as sodium hypochlorite but it is more stable and contains more available chlorine.

Advantages of textile bleaching-

a. Textile bleaching gives permanent whiteness.

b. It gives a high degree of brightness.

c. Negligible degradation of fiber (1-2% weight loss for cellulosic fibers and no attack on the polymeric chains in the synthetic fibers).

d. Lower environmental impact of wastewater (negligible level of COD).

e. Versatile bleaching agent for cellulosic, synthetics, and blends, especially poly-cotton blends. It is also safe for those synthetic fibers that are sensitive to alkalis.

f. Non-sensitive to metal ions such as iron and water hardness under acidic conditions.

Disadvantages of textile bleaching-

a. Textile bleaching is expensive as compared to H₂O₂

b. It can’t be used for wool and silk.

c. Chlorine dioxide is highly corrosive to metals and toxic in nature.

d. Bleaching in neutral and acidic pH damages cotton.

e. It may reduce fiber strength.

Conclusion

Overall bleach is essential for textiles such as denim the industry for color fading.