Fibres, Yarns and Fabrics Chapter 9
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Questions and Answers

What is the main effect of mercerisation on cotton fibres?

  • It decreases the dye-ability of the fibre.
  • It permanently weakens the fibre structure.
  • It reduces the surface lustre of the fibre.
  • It increases the fibre's moisture absorbency. (correct)

    • How does mercerisation affect the cross-sectional shape of the cotton fibre?

  • It maintains the kidney shape.
  • It leads to an irregular shape.
  • It changes from circular to kidney-shaped.
  • It becomes more circular from kidney-shaped. (correct)

    • What is one result of increased hydrogen bonding during the mercerisation process?

  • A reduction in the fibre's moisture absorbency.
  • A decrease in tensile strength of the fibre.
  • A less effective dye absorption.
  • A 20% increase in fibre strength. (correct)

    • What happens to the fibre's regain at 65% relative humidity and 20°C after mercerisation?

    <p>It increases by about 25%.</p> Signup and view all the answers

    What effect does tension during sodium hydroxide treatment have on cotton fibres?

    <p>It prevents the fibre from shrinking.</p> Signup and view all the answers

    How does mercerisation influence the quantity of dye needed for cotton fabrics?

    <p>Less dye is needed for a given shade depth.</p> Signup and view all the answers

    What is a notable physical change that occurs in cotton fibres due to mercerisation?

    <p>The fibres gain a shiny surface.</p> Signup and view all the answers

    What additional benefit does mercerisation provide regarding the accessibility of moisture?

    <p>Moisture penetration is facilitated through swelling.</p> Signup and view all the answers

    What is the primary impurity found in raw wool after shearing?

    <p>Grease</p> Signup and view all the answers

    What percentage of clean wool is typically yielded after scouring wool from sheep raised in conventional grazing conditions?

    <p>65%</p> Signup and view all the answers

    Which layer of wool fiber is responsible for hydrophobic properties?

    <p>Epicutical layer</p> Signup and view all the answers

    What is the typical residual grease percentage in scoured wool that aids in fiber processing?

    <p>0.5%</p> Signup and view all the answers

    Which type of sheep is mentioned as producing wool with minimal amounts of vegetable matter?

    <p>Merino sheep</p> Signup and view all the answers

    In which layer of wool fiber are the flat scale-like cells found?

    <p>Scale-cell layer</p> Signup and view all the answers

    Which of the following fibres is categorized as a natural animal fibre?

    <p>Silk</p> Signup and view all the answers

    What type of matter accounts for variations in the impurities of raw wool?

    <p>Agricultural region</p> Signup and view all the answers

    What is the purpose of treating pulp with alkali in the production of alkali cellulose?

    <p>To reduce the polymer chain lengths</p> Signup and view all the answers

    What is the main characteristic of viscose compared to cotton?

    <p>Higher moisture-absorbing properties</p> Signup and view all the answers

    What effect does the aging process of alkali cellulose have on the polymer chain lengths?

    <p>It shortens chains to optimize viscosity</p> Signup and view all the answers

    What happens to the fibre during the regeneration process in the acid bath?

    <p>It shrinks and develops a wrinkled appearance</p> Signup and view all the answers

    What is the main chemical reaction involved in converting alkali cellulose to cellulose xanthate?

    <p>Alkali cellulose reacts with carbon disulphide</p> Signup and view all the answers

    Which property of viscose makes it feel different compared to cotton?

    <p>Its amorphous structure</p> Signup and view all the answers

    What is a significant drawback of viscose compared to cotton?

    <p>Weakness against acids and bleaching agents</p> Signup and view all the answers

    Why do viscose fabrics tend to feel cold compared to cotton?

    <p>Higher thermal conductivity</p> Signup and view all the answers

    What is the primary content of bast fibres?

    <p>65%–75% cellulose and other components</p> Signup and view all the answers

    Which process is NOT used for retting flax fibres?

    <p>Steam retting</p> Signup and view all the answers

    What is the main source of linen?

    <p>Flax</p> Signup and view all the answers

    Which of the following statements about flax is true?

    <p>Flax seeds can be used to produce linseed oil</p> Signup and view all the answers

    How are coarser fibres primarily used?

    <p>In brushes, brooms, and door mats</p> Signup and view all the answers

    What happens to dew retted flax compared to dam retted flax?

    <p>It is darker in color</p> Signup and view all the answers

    What is the role of pectin in bast fibres?

    <p>It helps in binding the fibres together</p> Signup and view all the answers

    Which of the following fibres has a higher cellulose content compared to bast fibres?

    <p>Cotton</p> Signup and view all the answers

    What type of polymers are polyamides, polyurethanes, and aramids examples of?

    <p>Addition polymers</p> Signup and view all the answers

    Which functional groups can cause hydrolysis in linear polymers, leading to degradation?

    <p>Amide and ester</p> Signup and view all the answers

    What characteristic do addition polymers have that makes them more crystalline than condensation polymers?

    <p>Higher degree of polymerization</p> Signup and view all the answers

    What is a key feature of monomers used in addition polymerization?

    <p>They must contain double bonds.</p> Signup and view all the answers

    Which of the following is NOT a type of polyester mentioned?

    <p>Polypropylene</p> Signup and view all the answers

    What is one effect of internal cross-linking in polymers like cotton and viscose?

    <p>Improved dimensional stability</p> Signup and view all the answers

    Which type of polymers are characterized by having the same number of atoms in the structural unit as the monomer?

    <p>Addition polymers</p> Signup and view all the answers

    What is a characteristic of branched chain polymers?

    <p>They can form cross-linked structures.</p> Signup and view all the answers

    Study Notes

    Mercerising Process

    • Mercerising increases the cotton fibre's moisture regain by approximately 25% at 65% relative humidity and 20°C.
    • It causes physical changes that enhance the fibre's value, including increased strength (about 20%) due to increased hydrogen bonding.
    • Tension during the sodium hydroxide treatment prevents fibre shrinkage, enhancing surface lustre as the fibre's cross-section becomes more circular.
    • The treatment dramatically increases moisture absorbency, contributing to garment comfort and dye-ability, allowing for less dye usage for the desired shade.

    Stem Fibres

    • Stem or bast fibres are derived from the inner vascular area of dicotyledonous plants and are thick-walled cells cemented by pectin.
    • They consist of 65%-75% cellulose, compared to cotton, with the remaining components being hemicellulose, pectin, and lignins.
    • Major bast fibres include flax (source of linen), ramie, hemp, jute, and kenaf. Linen blends with synthetic fibres like polyester are popular in fashion.

    Flax Fiber

    • Flax is obtained from Linum usitatissimum, thriving in temperate to sub-tropical climates.
    • Flax oil (linseed oil) is derived from its seeds, while the fibers are released via retting processes, including dam, dew, and tank retting.
    • Dam retting involves soaking bundles in water for about 10 days, while dew retting relies on rainfall and dew.
    • Tank retting uses heated water for expedited retting, improving fibre quality.

    Wool Fiber

    • Wool is the primary protein fibre, with global production around 1.2 million tonnes as of 2008.
    • Raw wool, post-shearing, contains impurities like grease and vegetable matter, with a yield of about 65% clean wool after scouring.
    • Wool structure consists of four regions:
      • The epicutical layer, a waterproof membrane absorbing water vapour.
      • The scale-cell layer, featuring overlapping, flat, scale-like cells.

    Viscose

    • Viscose fibres exhibit lower crystallinity (35%-40%) compared to cotton (65%-70%), resulting in a weaker fabric.
    • Produced from alkali cellulose, viscose is processed through spinning and hardening in a sulfuric acid bath.
    • Viscose has higher moisture absorption properties but lower resistance to acids and bleaching, making it prone to discolouration and weakening.

    Bamboo Fiber

    • Bamboo fiber is created from cellulose pulp derived from the bamboo plant, categorized as viscose rayon.

    Synthetic Fibers

    • Synthetic fibers include polyester, polyamide, polyolefin, polyvinyl, polyurethane, and aramids, made by transforming natural polymers or synthetic processes.
    • Addition polymers are formed by directly adding monomers, resulting in stronger C-C bonds and higher crystallinity compared to condensation polymers.
    • Fibres can be linear or branched, with internal cross-linking improving fabric dimensional stability and reducing shrinkage tendencies.

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    Explore the impact of mercerising on cotton fibres in this quiz. Learn how treatments can enhance the physical and chemical properties of the fibre, ultimately adding value to the finished fabric. Test your understanding of fibre treatments and their effects on textile properties.

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