GATE (TF) Textile 2016 Question Paper Solution | GATE/2016/TF/35

Rayon is typically produced using the wet spinning method. In this method, cellulose from wood pulp or other sources is first dissolved in a chemical solution to create a viscous solution called “dope.” This dope is then extruded through a spinneret (a device with many small holes) into a bath of chemicals that cause the fibers to solidify and form into long, continuous strands.
As the dope is extruded through the spinneret, it comes into contact with a coagulating bath, typically consisting of sulfuric acid or a similar compound. This causes the cellulose molecules to precipitate and form into solid fibers. The fibers are then washed and treated with additional chemicals to remove any remaining impurities and improve their properties.
The wet spinning method is the most common method for producing rayon, although there are other methods such as dry spinning and melt spinning that can also be used.

Aramid fibers, such as Kevlar and Nomex, are spun using a process called “dry spinning.” This method involves dissolving the polymer in a solvent, which is then extruded through a spinneret to form fibers. The fibers are then solidified by evaporating the solvent in a controlled manner.
Here are the basic steps involved in the dry spinning process for aramid fibers:
Polymer synthesis: The aramid polymer is first synthesized through a chemical reaction involving monomers such as para-phenylenediamine (PPD) and terephthalic acid (TPA).
Polymer spinning solution: The aramid polymer is dissolved in a solvent such as sulfuric acid to create a spinning solution. Other additives may also be added to improve the properties of the fibers.
Spinneret extrusion: The spinning solution is extruded through a spinneret, which is a metal plate with small holes. The size and shape of the holes determine the diameter and cross-sectional shape of the fibers.
Fiber solidification: As the fibers are extruded from the spinneret, they come into contact with a stream of air or other gas that causes the solvent to evaporate. This solidifies the fibers into their final form.
Fiber collection: The solidified fibers are collected on a rotating drum or other collection device. The fibers may be wound into a continuous thread or chopped into shorter lengths depending on the intended application.
Post-treatment: The aramid fibers may undergo additional processing steps such as heat treatment or surface treatment to improve their strength, stiffness, or other properties.
Dry spinning is a versatile and widely used method for producing aramid fibers, which are known for their high strength, durability, and resistance to heat and chemicals.

Ultra-high molecular weight polyethylene (UHMWPE) is typically produced through a polymerization process called “solution polymerization.” Here are the basic steps involved in the production of UHMWPE:
Monomer synthesis: Ethylene gas is first converted into ethylene monomer, typically through a high-pressure process that involves reacting ethylene with a catalyst such as chromium oxide.
Polymerization: The ethylene monomer is then polymerized in a solvent such as naphtha or hexane using a catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. The polymerization is typically carried out at a relatively low temperature and pressure to prevent the formation of branching in the polymer chains.
Precipitation: After the polymerization is complete, the UHMWPE is separated from the solvent by adding a non-solvent such as ethanol or water. This causes the UHMWPE to precipitate out of the solution as fine particles.
Washing and drying: The UHMWPE particles are then washed and dried to remove any remaining solvent and impurities.
Powder consolidation: The UHMWPE particles may be consolidated into a solid form through a process called “powder consolidation.” This involves compressing the particles under high pressure and temperature to form a solid block or sheet.
Melt processing: The UHMWPE can also be melt-processed by melting the powder or solid block and extruding it into a desired shape or form.
UHMWPE is known for its exceptional strength, toughness, and wear resistance, and is used in a variety of applications such as medical implants, protective gear, and industrial components.

Polyesters are a class of polymers that are widely used in a variety of applications, including textiles, packaging, and plastics. The most common type of polyester is polyethylene terephthalate (PET), which is typically produced using the following manufacturing process:
Monomer synthesis: The raw materials for PET production are purified terephthalic acid (PTA) and monoethylene glycol (MEG). PTA is synthesized from petroleum-derived feedstocks, while MEG can be produced from either petroleum or renewable sources such as corn or sugarcane.
Polymerization: PTA and MEG are reacted together in a reactor vessel in the presence of a catalyst and a small amount of a co-monomer such as isophthalic acid. The reaction produces a low molecular weight polymer called a prepolymer.
Solid state polymerization: The prepolymer is then heated under vacuum to remove any remaining water or other impurities, and then subjected to solid-state polymerization at high temperature and low pressure. This step increases the molecular weight of the polymer and improves its properties.
Melt processing: The resulting PET polymer is melted and extruded through a spinneret to form fibers, or molded into a desired shape such as a bottle or film.
Finishing: The PET product may undergo additional processing steps such as stretching, heat setting, or coating to improve its properties and performance.
Polyester production is a highly efficient and automated process that produces a versatile and widely used polymer. However, it is also associated with environmental concerns due to its dependence on petroleum-derived feedstocks and its potential to contribute to plastic waste and pollution.