Fibres, Yarns and Fabrics Chapter 9 Answers PDF

Fibres, Yarns and Fabrics Chapter 9 Answers 1. What is the main effect of mercerisation on cotton fibres? A. It decreases the dye-ability of the fibre. B. It permanently weakens the fibre structure. C. It reduces the surface lustre of the fibre. D. It increases the fibre's moisture abs...

Fibres, Yarns and Fabrics Chapter 9 Answers 1. What is the main effect of mercerisation on cotton fibres? A. It decreases the dye-ability of the fibre. B. It permanently weakens the fibre structure. C. It reduces the surface lustre of the fibre. D. It increases the fibre's moisture absorbency. Answer: It increases the fibre's moisture absorbency. (D) Mercerisation enhances the moisture absorbency, making cotton garments more comfortable. 2. How does mercerisation affect the cross-sectional shape of the cotton fibre? A. It maintains the kidney shape. B. It leads to an irregular shape. C. It changes from circular to kidney-shaped. D. It becomes more circular from kidney-shaped. Answer: It becomes more circular from kidney-shaped. (D) Mercerisation transforms the fibre's cross-section to be more circular, enhancing reflective properties. 3. What is one result of increased hydrogen bonding during the mercerisation process? A. A reduction in the fibre's moisture absorbency. B. A decrease in tensile strength of the fibre. C. A less effective dye absorption. D. A 20% increase in fibre strength. Answer: A 20% increase in fibre strength. (D) Increased hydrogen bonding contributes to significant gains in strength during mercerisation. 4. What happens to the fibre's regain at 65% relative humidity and 20°C after mercerisation? A. It stays the same as untreated fibres. B. It increases by about 25%. C. It decreases significantly. D. It becomes unpredictable. Answer: It increases by about 25%. (B) Mercerisation leads to an approximate 25% increase in fibre regain under specified conditions. 5. What effect does tension during sodium hydroxide treatment have on cotton fibres? A. It causes the fibre to bulk up. B. It increases the dye-ability of the fibre. C. It decreases the strength of the fibre. D. It prevents the fibre from shrinking. Answer: It prevents the fibre from shrinking. (D) Keeping the fabric under tension prevents shrinkage during the mercerisation process. 6. How does mercerisation influence the quantity of dye needed for cotton fabrics? A. Less dye is needed for a given shade depth. B. Dye becomes ineffective altogether. C. More dye is required for a darker shade. D. Dye absorption is completely eliminated. Answer: Less dye is needed for a given shade depth. (A) The dye-ability of mercerised fibres increases, requiring lower quantities of dye for desired depths. 7. What is a notable physical change that occurs in cotton fibres due to mercerisation? A. The fibres lose their strength. B. The fibres become brittle. C. The fibres gain a shiny surface. D. The fibres retain their original shape. Answer: The fibres gain a shiny surface. (C) The mercerisation process enhances the surface lustre of cotton fibres. 8. What additional benefit does mercerisation provide regarding the accessibility of moisture? A. Moisture access is limited to the surface only. B. It makes fibres completely waterproof. C. Moisture can no longer penetrate the fibres. D. Moisture penetration is facilitated through swelling. Answer: Moisture penetration is facilitated through swelling. (D) The swelling of fibres during mercerisation increases moisture accessibility, improving absorbency. 9. What is the primary impurity found in raw wool after shearing? A. Grease B. Chemical residues C. Color dyes D. Synthetic fibers Answer: Grease (A) Raw wool is known to contain impurities including grease, swint, dirt, and vegetable matter. 10. What percentage of clean wool is typically yielded after scouring wool from sheep raised in conventional grazing conditions? A. 50% B. 75% C. 65% D. 85% Answer: 65% (C) Under conventional grazing conditions, the yield of scoured wool is approximately 65%. 11. Which layer of wool fiber is responsible for hydrophobic properties? A. Cuticle layer B. Scale-cell layer C. Epicutical layer D. Endocuticle layer Answer: Epicutical layer (C) The epicutical layer is a thin hydrophobic membrane that repels water droplets. 12. What is the typical residual grease percentage in scoured wool that aids in fiber processing? A. 1.0% B. 2.0% C. 0.1% D. 0.5% Answer: 0.5% (D) Scoured wool typically retains about 0.5% residual grease which assists in processes like carding. 13. Which type of sheep is mentioned as producing wool with minimal amounts of vegetable matter? A. Merino sheep B. Dorper sheep C. Hampshire sheep D. Suffolk sheep Answer: Merino sheep (A) Merino sheep raised under shedded conditions show minimal amounts of vegetable matter and dirt in their fleece. 14. In which layer of wool fiber are the flat scale-like cells found? A. Scale-cell layer B. Epicutical layer C. Matrix layer D. Core layer Answer: Scale-cell layer (A) The scale-cell layer contains flat scale-like cells which overlap each other. 15. Which of the following fibres is categorized as a natural animal fibre? A. Nylon B. Acrylic C. Silk D. Polyester Answer: Silk (C) Silk is a natural animal fibre, while nylon, polyester, and acrylic are man-made. 16. What type of matter accounts for variations in the impurities of raw wool? A. Soil type B. Weather patterns C. Agricultural region D. Breeding techniques Answer: Agricultural region (C) The quantities of impurities in raw wool can vary depending on the agricultural region where the animal has grazed. 17. What is the purpose of treating pulp with alkali in the production of alkali cellulose? A. To enhance the strength of the fibre B. To reduce the polymer chain lengths C. To form a viscous liquid for spinning D. To increase the crystallinity of the pulp Answer: To reduce the polymer chain lengths (B) Treating the pulp with alkali reduces the polymer chain lengths, which is essential for viscosity in the spinning process. 18. What is the main characteristic of viscose compared to cotton? A. Stronger fibre in both dry and wet states B. Greater resistance to acids and bleaching agents C. Higher moisture-absorbing properties D. Higher crystallinity Answer: Higher moisture-absorbing properties (C) Viscose has a large number of polar hydroxyl groups that contribute to its higher moisture-absorbing properties. 19. What effect does the aging process of alkali cellulose have on the polymer chain lengths? A. It eliminates all hydrogen bonds B. It shortens chains to optimize viscosity C. It produces longer chains to improve strength D. It increases the crystallinity of the fibre Answer: It shortens chains to optimize viscosity (B) The aging process controls the chain lengths to ensure they are short enough for optimum viscosity while maintaining good physical properties. 20. What happens to the fibre during the regeneration process in the acid bath? A. It becomes more crystalline B. It shrinks and develops a wrinkled appearance C. It dissolves completely D. It expands significantly Answer: It shrinks and develops a wrinkled appearance (B) As regeneration occurs toward the inside of the fibre, the fibre shrinks, resulting in a wrinkled cross-section. 21. What is the main chemical reaction involved in converting alkali cellulose to cellulose xanthate? A. Cellulose xanthate is formed by heating B. Cellulose xanthate is created from cotton fibre C. Alkali cellulose reacts with glucose D. Alkali cellulose reacts with carbon disulphide Answer: Alkali cellulose reacts with carbon disulphide (D) The alkali cellulose is reacted with carbon disulphide to form cellulose xanthate. 22. Which property of viscose makes it feel different compared to cotton? A. Its resistance to mold B. Its amorphous structure C. Its higher crystallinity D. Its lower moisture absorption Answer: Its amorphous structure (B) Viscose is amorphous in nature, which contributes to its distinct feel compared to cotton. 23. What is a significant drawback of viscose compared to cotton? A. Lower moisture absorption B. Higher cost of production C. Weakness against acids and bleaching agents D. Higher resistance to discolouration Answer: Weakness against acids and bleaching agents (C) Viscose has much lower resistance to acids and bleaching agents, making it more susceptible to damage. 24. Why do viscose fabrics tend to feel cold compared to cotton? A. Increased air permeability B. Higher thermal conductivity C. Greater absorbency of sweat D. Lower moisture levels Answer: Higher thermal conductivity (B) Viscose's structure leads to higher thermal conductivity, which can make it feel cool against the skin. 25. What is the primary content of bast fibres? A. High cellulose content B. 100% cellulose C. Only lignins D. 65%–75% cellulose and other components Answer: 65%–75% cellulose and other components (D) Bast fibres have a lower cellulose content, consisting of 65%–75% cellulose along with hemi-cellulose, pectin, and lignins. 26. Which process is NOT used for retting flax fibres? A. Steam retting B. Dew retting C. Dam retting D. Tank retting Answer: Steam retting (A) Steam retting is not mentioned as a process for retting flax fibres; the processes include dew, tank, and dam retting. 27. What is the main source of linen? A. Flax B. Jute C. Hemp D. Ramie Answer: Flax (A) Flax is identified as the main source of linen. 28. Which of the following statements about flax is true? A. Flax can only grow in temperate climates B. Flax is primarily used for making fishing nets C. Flax stems contain only fiber D. Flax seeds can be used to produce linseed oil Answer: Flax seeds can be used to produce linseed oil (D) Flax seeds, when crushed, yield flax oil known as linseed oil. 29. How are coarser fibres primarily used? A. To produce fine linen B. In brushes, brooms, and door mats C. In high-class fashion shirtings D. For making synthetic textiles Answer: In brushes, brooms, and door mats (B) Coarser fibres are typically used in making brushes, brooms, and door mats. 30. What happens to dew retted flax compared to dam retted flax? A. It is lighter in color B. It has a higher water content C. It is darker in color D. It requires longer processing time Answer: It is darker in color (C) Dew retted flax is noted to be darker than fibre that has been dam or tank retted. 31. What is the role of pectin in bast fibres? A. It is used to create linseed oil B. It is the main structural component C. It helps in binding the fibres together D. It decreases the fibre's strength Answer: It helps in binding the fibres together (C) Pectin is a non-cellulose material that helps in cementing the fibres together. 32. Which of the following fibres has a higher cellulose content compared to bast fibres? A. Kenaf B. Jute C. Hemp D. Cotton Answer: Cotton (D) Cotton has a higher cellulose content compared to bast fibres, which consist of 65%–75% cellulose.