GATE (TF) Textile 2018 Question Paper Solution | GATE/2018/TF/39

Question 39 (Textile Technology & Fibre Science)

Match the dye-fibre in Group I with the interactions in Group II.

Group IGroup II
P. Reactive dye on cotton1. Van der Waals forces
Q. Disperse dye on polyester2. Covalent bonds
R. Vat dye on cotton3. Electrostatic bonds
S. Basic dye on acrylic4. Mechanical entrapment
(A)P-1, Q-2, R-4, S-3
(B)P-1, Q-2, R-3, S-4
(C)P-2, Q-1, R-4, S-3
(D)P-2, Q-1, R-3, S-4
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Frequently Asked Questions | FAQs

What are reactive dyes for cotton process?

Reactive dyes are a type of water-soluble dyes that are commonly used in the textile industry for dyeing cotton and other cellulosic fibers. Reactive dyes react chemically with the cellulose fibers, forming a covalent bond between the dye molecule and the fiber. This reaction allows the dye to become a part of the fabric, resulting in a strong and durable color that is resistant to washing and fading.

The reactive dyeing process involves several steps, including:

Preparation of the fabric: The cotton fabric is pre-treated with chemicals to remove any impurities and to improve the dye uptake.

Dyeing: The fabric is immersed in a solution of the reactive dye and a salt, which helps to promote the dye uptake. The dye molecules react with the cellulose fibers, forming covalent bonds and creating a strong and durable color.

Washing and rinsing: The fabric is washed and rinsed to remove any unreacted dye molecules and other impurities.

Fixation: The fabric is treated with an alkali solution, which helps to fix the dye molecules to the cellulose fibers and to improve the color fastness.

Reactive dyes offer several advantages over other types of dyes, including a wide range of bright and vibrant colors, excellent color fastness, and low environmental impact.

Reactive dyeing is also a cost-effective and efficient process, making it a popular choice for textile manufacturers.

What is dispersed dye for polyester?

Dispersed dye is a type of dye that is commonly used to color polyester fabrics. Polyester is a synthetic fiber that is resistant to water and stains, but it can be difficult to dye because it is hydrophobic, which means it repels water. Dispersed dyes are specially designed to overcome this issue by dispersing the dye molecules evenly throughout the fabric.
Dispersed dyes are usually insoluble in water, which means they need to be dispersed in a carrier or dispersing agent to be applied to the polyester fabric. These dispersing agents help the dye to penetrate the fibers and create an even color throughout the fabric.
Dispersed dyes are popular for dyeing polyester fabrics because they can produce bright, vibrant colors that are resistant to fading and washing. They are commonly used in the textile industry to dye fabrics such as clothing, curtains, and upholstery.

How vat dyes are applied to cotton?

Vat dyes are a type of dye that can be used to color cotton fabrics. They are water-insoluble and require a reducing agent and an alkaline environment to become soluble and form a chemical bond with the cotton fibers. Here is a general process for applying vat dyes to cotton:

Scouring: The cotton fabric is first washed to remove any impurities, such as dirt or natural oils, that could prevent the dye from penetrating the fibers. This is usually done using a strong detergent and high heat.

Pre-treatment: The cotton fabric is then treated with a reducing agent, such as sodium hydrosulfite, to convert the insoluble vat dye into a soluble form that can bond with the fabric. This is typically done in an alkaline solution, such as sodium hydroxide or soda ash.

Dyeing: The cotton fabric is immersed in the vat dye solution, which contains the soluble form of the dye. The fabric is then agitated to ensure that the dye penetrates the fibers evenly. The fabric is typically held in the dye bath at a temperature between 50-60°C for 30-60 minutes, depending on the desired color depth.

Oxidation: Once the fabric has been dyed, it is removed from the dye bath and exposed to air, which causes the dye to oxidize and become insoluble again. This step is crucial to ensure that the color is permanent and does not fade with washing or exposure to light.

Washing: The fabric is then washed thoroughly to remove any excess dye and reducing agent, and to ensure that the color is set. This may involve several rinses with detergent and hot water.

Drying: Finally, the fabric is dried and finished according to the desired specifications, such as by pressing or steaming to remove wrinkles.

Overall, the process of applying vat dyes to cotton is complex and requires careful control of temperature, pH, and timing to ensure that the dye penetrates the fibers evenly and produces a consistent and durable color.

Why does acrylic take basic dye?

Acrylic fibers are synthetic fibers that are made from a polymer called polyacrylonitrile. Unlike natural fibers such as cotton or wool, acrylic fibers are hydrophobic, meaning they do not absorb water easily. This property makes it difficult to dye acrylic fibers using traditional dyeing techniques.

Basic dyes, also known as cationic dyes, are a type of dye that is positively charged and can bond to negatively charged fibers. Acrylic fibers have a slightly negative charge on their surface, which makes them an ideal candidate for basic dyeing.

During the dyeing process, the basic dye is dissolved in water and a cationic dye fixative is added to the solution. The fibers are then immersed in the solution, and the cationic dye fixative helps the positively charged dye molecules to bond with the negatively charged acrylic fibers.

Once the dye has bonded with the fibers, the acrylic fibers can be washed and rinsed to remove any excess dye, and then dried. Basic dyes are often preferred for dyeing acrylic fibers because they produce bright, vibrant colors that are resistant to fading, and the dye bonds strongly to the fibers, creating a long-lasting color.

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