GATE (TF) Textile 2013 Question Paper Solution | GATE/2013/TF/36

Question 36 (Textile Engineering & Fibre Science)

Consider the following assertion [a] and reason [r] and choose the most appropriate answer
[a] Sodium cellulose xanthate formation is an essential unit operation in the production of viscose rayon
[r] It helps to reduce the degree of polymerization of cellulose

Answer / Solution

(A)[a] is right [r] is wrong
(B)[a] is right [r] is right
(C)[a] is wrong [r] is wrong
(D)[a] is wrong [r] is right
Answer / Solution
[Show Answer]

Option A

Frequently Asked Questions | FAQs

What is the process of viscose preparation?

Viscose rayon, also known simply as “rayon,” is a synthetic fiber that is made from cellulose, a natural polymer derived from wood pulp. The preparation of viscose rayon involves several steps, including:

Purification of cellulose: The cellulose is first extracted from wood pulp, cotton linters, or other sources of cellulose. The cellulose is then purified to remove impurities such as lignin, hemicellulose, and other non-cellulosic materials.

Alkali treatment: The purified cellulose is treated with a strong alkali, typically sodium hydroxide (NaOH), to form alkali cellulose. The alkali treatment swells and dissolves the cellulose, forming a viscous solution.

Xanthation: The alkali cellulose solution is then treated with carbon disulfide (CS2) to form cellulose xanthate, a yellowish-orange powder. The carbon disulfide reacts with the alkali cellulose to form a derivative that is soluble in a more polar medium.

Aging: The cellulose xanthate is aged for a period of time, typically several hours to several days, to allow the xanthate groups to fully develop and stabilize. This aging process is important for the subsequent steps of the viscose rayon production.

Dissolving in caustic soda: The aged cellulose xanthate is then dissolved in a dilute solution of sodium hydroxide (NaOH) to form a viscose solution. The sodium hydroxide converts the cellulose xanthate back into cellulose, which is now in a soluble form.
Filtration and degassing: The viscose solution is filtered to remove any remaining undissolved particles, and then degassed to remove air bubbles and other gases from the solution.

Spinning: The viscose solution is then extruded through spinnerets, which are fine holes, into a coagulating bath, typically containing sulfuric acid (H2SO4) or another acid. The coagulating bath causes the cellulose to precipitate and solidify into long fibers, which are then washed and neutralized to remove any residual chemicals.

Stretching and drying: The solidified cellulose fibers, now in the form of rayon filaments, are stretched to improve their strength and elasticity. The stretched filaments are then dried to remove excess moisture.

Finishing: The dried rayon filaments may undergo additional finishing processes, such as dyeing, bleaching, and/or sizing, to achieve the desired properties for the final viscose rayon product.

Once the finishing processes are complete, the viscose rayon fibers can be spun into yarns, woven into fabrics, and used in a wide range of textile applications, such as clothing, home textiles, and industrial textiles. Viscose rayon is known for its softness, drapability, and versatility, making it a popular choice for many textile applications.

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