GATE (TF) Textile 2009 Question Paper Solution | GATE/2009/TF/42

Question 42 (Textile Engineering & Fibre Science)

Consider the following statements:

P, Presence of iron and copper ions during bleaching with sodium chlorite is desirable.
Q, Sodium silicate is used as a stabilizer in bleaching of cotton with hydrogen peroxide.
R, Oil repellent finishes are based on fluorochemicals.
S, Sodium hydrosulphite is used as a reducing agent in vat printing.

(A)P, S
(B)Q, S
(C)P, R
(D)Q, R
[Show Answer]

Option D is correct.

Frequently Asked Questions | FAQs

What is the use of sodium silicate in bleaching with hydrogen peroxide?

Sodium silicate, also known as water glass or liquid glass, is a compound that is commonly used in bleaching processes, including bleaching with hydrogen peroxide. Sodium silicate serves several purposes and offers benefits in the bleaching process. Here are the main uses of sodium silicate in bleaching with hydrogen peroxide:

Stabilization of Hydrogen Peroxide: Sodium silicate helps stabilize hydrogen peroxide, which is a reactive and unstable compound. Hydrogen peroxide rapidly decomposes when exposed to heat, light, or certain impurities. Sodium silicate acts as a stabilizing agent, preventing the premature breakdown of hydrogen peroxide and extending its shelf life. This allows hydrogen peroxide to remain effective for a longer duration during the bleaching process.

pH Adjustment: Sodium silicate has alkaline properties and is used to adjust and maintain the pH level in the bleaching bath. It helps create an optimal pH environment for the bleaching process, as hydrogen peroxide functions most efficiently in alkaline conditions. The alkaline pH also enhances the bleaching action by facilitating the breakdown of dyes and other impurities.
Sequestration of Metal Ions: Sodium silicate has chelating properties, meaning it can sequester or bind with metal ions present in the fabric or the water used in the bleaching process. Metal ions, such as iron or copper, can catalyze the decomposition of hydrogen peroxide, leading to reduced bleaching effectiveness. Sodium silicate helps prevent this by binding to metal ions, thereby reducing their ability to degrade hydrogen peroxide and ensuring its maximum bleaching potential.
Dispersing and Soil Removal: Sodium silicate acts as a dispersing agent, aiding in the removal of soil, dirt, and impurities from the fabric. It helps loosen and disperse these particles, allowing them to be easily rinsed away during the bleaching process. This improves the overall cleanliness and whiteness of the fabric.

Fabric Protection: Sodium silicate can provide some level of fabric protection during the bleaching process. It forms a thin film or coating on the fabric surface, which acts as a barrier between the fabric and the bleaching solution. This helps reduce the risk of excessive damage or fiber degradation that can occur with prolonged exposure to hydrogen peroxide.

It’s important to note that the specific concentration and usage of sodium silicate may vary depending on the fabric type, desired bleaching effect, and other factors. Additionally, sodium silicate should be used in accordance with safety guidelines and handling instructions, as it can be caustic and harmful if mishandled.

Overall, sodium silicate plays a valuable role in bleaching with hydrogen peroxide, contributing to the stabilization, pH adjustment, metal ion sequestration, soil removal, and fabric protection aspects of the bleaching process.

What is oil repellent finish?

Oil repellent finish, also known as oil-resistant finish or oil-repellency treatment, is a textile finishing process applied to fabrics to make them resistant to oil-based substances and liquids. The finish creates a protective barrier on the fabric surface, preventing the absorption or penetration of oils, greases, and other hydrophobic liquids. This treatment is commonly used in various industries, including workwear, outdoor apparel, and upholstery, where resistance to oil stains and contamination is desired.
Here are some key aspects and benefits of an oil repellent finish:

Oil and Liquid Resistance: The primary purpose of an oil repellent finish is to make the fabric resistant to oil-based substances. The finish forms a barrier on the fabric surface, making it difficult for oils and hydrophobic liquids to be absorbed or penetrate into the fabric. This helps prevent oil stains and contamination, making the fabric easier to clean and maintain.
Stain Resistance: By repelling oils and greases, an oil repellent finish also provides resistance against other types of stains. It helps prevent the penetration of common stains caused by food, beverages, and other liquids that may contain oils or oil-based components. This makes the fabric more resistant to staining, ensuring a cleaner and more presentable appearance.

Easy Cleaning and Maintenance: Fabrics with an oil repellent finish are easier to clean and maintain. The oil-resistant barrier prevents oils from being absorbed into the fabric fibers, allowing stains to be easily wiped off or rinsed away. This reduces the need for aggressive cleaning methods or prolonged soaking, simplifying the fabric care process.

Extended Fabric Lifespan: The oil repellent finish can contribute to the longevity of the fabric. By preventing oil absorption, it helps protect the fabric fibers from the damaging effects of oils and greases, such as weakening, discoloration, or degradation. This can extend the fabric’s lifespan, allowing it to retain its appearance and performance over a longer period.

Breathability and Comfort: An effective oil repellent finish maintains the breathability and comfort properties of the fabric. It forms a protective barrier on the surface without significantly affecting the fabric’s air and moisture permeability. This allows the fabric to remain breathable, ensuring comfort during wear.

Versatility: Oil repellent finishes can be applied to various types of fabrics, including natural fibers like cotton and wool, as well as synthetic fibers like polyester and nylon. This makes it a versatile treatment suitable for a wide range of textile applications, including apparel, outerwear, upholstery, and industrial fabrics.

It’s important to note that oil repellent finishes can vary in their durability and effectiveness. The performance of the finish may diminish over time or with repeated laundering, requiring reapplication or retreatment to maintain the desired level of oil repellency. Additionally, specific care instructions provided by the fabric manufacturer should be followed to ensure the longevity and effectiveness of the oil repellent finish.

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