GATE (TF) Textile 2013 Question Paper Solution | GATE/2013/TF/19

Question 19 (Textile Engineering & Fibre Science)

Disperse dye cannot generally be fixed on polyester by

(A)Superheated steam at 180oC
(B)Saturated steam at 130oC
(C)Dry heat at 200oC
(D)Saturated steam at 100oC
Answer / Solution
[Show Answer]

Option D

Frequently Asked Questions | FAQs

Why polyester is dyed with disperse dye and in high temperature? | Are dispersed dyes used to color polyester fibres?

Polyester is a synthetic fiber that has a high melting point and is inherently hydrophobic, meaning it does not readily absorb water. These characteristics make it difficult for conventional water-based dyes to penetrate and bond with polyester fibers. Disperse dyes, which are a type of dye specifically designed for dyeing polyester and other synthetic fibers, are used to overcome these challenges.
Disperse dyes are typically small molecular weight dyes that are finely ground into a powder form. They have low solubility in water, but high solubility in organic solvents, such as dimethylformamide (DMF) or dimethylacetamide (DMAc), which are used as dye carriers. When disperse dyes are dissolved in these organic solvents, they can effectively penetrate the hydrophobic polyester fibers and bond with them through physical and van der Waals forces, resulting in coloration.
The use of high temperature is essential in the dyeing of polyester with disperse dyes for several reasons:

Improved dye solubility: Disperse dyes have low solubility in water, and their solubility increases with temperature. Therefore, higher temperatures are necessary to dissolve disperse dyes in the organic solvents used as dye carriers, allowing them to effectively penetrate and dye the polyester fibers.
Increased dye diffusion: High temperature promotes the diffusion of dyes into the polyester fibers, allowing the dye molecules to migrate from the dye bath into the fiber matrix and bond with the polyester molecules. This helps to achieve a more uniform and even dye distribution throughout the polyester fabric.
Accelerated dyeing rate: The rate of dyeing is generally slower at lower temperatures, and polyester, being a thermally stable fiber, requires higher temperatures to accelerate the dyeing process and achieve a satisfactory coloration level within a reasonable time frame.
Enhanced dye fixation: Polyester fibers require heat to improve the fixation or bonding of the disperse dye molecules to the fiber matrix. The high temperature during dyeing helps to promote the chemical bonding between the dye molecules and the polyester fibers, leading to improved wash and light fastness properties.

It’s important to note that the specific dyeing conditions, including temperature, time, and dye concentration, may vary depending on the type of disperse dye, the polyester fiber type, and the desired color outcome. Therefore, it is essential to follow the dye manufacturer’s instructions and recommended dyeing conditions for optimal results when dyeing polyester with disperse dyes.

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