GATE Textile Engineering Textile Fibres Syllabus

Textile Fibres syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Textile Fibres in GATE Textile Engineering, not a summary of it.

1. 1

   Classification of Textile Fibres

   5 topics

   • Essential Requirements of Fibre Forming Polymers
   • Gross and Fine Structures of Natural Fibres
     • Cotton
     • Wool
     • Silk
   • Introduction to Bast Fibres
   • Properties and Uses of Fibres
     • Natural Fibres
     • Man-made Fibres
     • Carbon Fibres
     • Aramid Fibres
     • Ultra-high Molecular Weight Polyethylene Fibres
   • Physical and Chemical Methods of Fibre Identification and Blend Analysis
2. 2

   Molecular Architecture and Phases

   11 topics

   • Amorphous and Crystalline Phases
   • Glass Transition and Crystallization
   • Melting and Factors Affecting Tg and Tm
   • Polymerization of Fibres
     • Nylon-6
     • Nylon-66
     • Poly(ethylene terephthalate)
     • Polyacrylonitrile
     • Polypropylene
   • Melt Spinning Processes
     • PET
     • Polyamide
     • Polypropylene
   • Preparation of Spinning Dope
   • Spinning Techniques
     • Wet Spinning
     • Dry Spinning
     • Dry-jet-wet Spinning
     • Gel Spinning
   • Spinning of Regenerated Cellulosic Fibres
     • Acrylic
     • Viscose
     • Polynosic
     • Lyocell
   • Post Spinning Operations
     • Drawing
     • Heat Setting
     • Tow-to-Top Conversion
   • Spin Finish Composition and Applications
   • Texturing Methods
3. 3

   Investigating Fibre Structure

   5 topics

   • Methods of Investigating Fibre Structure
     • Density
     • X-ray Diffraction
     • Birefringence
     • Optical and Electron Microscopy
     • I.R. Spectroscopy
     • Thermal Methods
   • Structure and Morphology of Man-made Fibres
   • Mechanical Properties of Fibres
   • Moisture Sorption of Fibres
   • Fibre Structure-Property Correlation

Textile Fibres flashcards for GATE Textile Engineering

18 of 51 cards from the Textile Fibres deck — real questions with worked answers.

1. What are the essential requirements of a fibre-forming polymer (list the key structural criteria)?

   A fibre-forming polymer must have: (1) high and uniform molecular weight (linear chains, $DP \geq 100$); (2) linear, regular chain structure with no bulky side groups; (3) capacity for orientation and crystallization; (4) strong intermolecular forces (H-bonds, dipole, van der Waals); (5) flexibility yet stiffness balance; (6) chemical, thermal and light stability; and (7) ability to be drawn/spun into filaments.

2. Why is a high degree of polymerization essential for fibre formation, and what is the typical minimum?

   A high degree of polymerization ($DP$) provides enough chain length for sufficient intermolecular bonding and entanglement to give strength. Below a critical $DP$ the polymer is brittle and lacks tenacity. Fibre-forming polymers typically need $DP \geq 100$ (molecular weight roughly $10{,}000$–$100{,}000$).

3. Distinguish 'gross structure' from 'fine structure' of a natural fibre.

   Gross structure refers to the overall morphology visible under a light microscope (length, cross-sectional shape, convolutions, lumen, scales, cuticle). Fine structure refers to the sub-microscopic/molecular arrangement: fibrils, microfibrils, crystalline and amorphous regions, orientation and the degree of crystallinity.

4. Describe the longitudinal and cross-sectional gross structure of cotton fibre.

   Longitudinally cotton appears as a flat, twisted ribbon with characteristic convolutions (natural twists). In cross-section it is kidney-bean/elliptical shaped with a central hollow lumen. It has a cuticle, primary wall, secondary wall (bulk of cellulose), and the lumen.

5. What is the chemical composition and crystallinity of cotton?

   Cotton is about $88$–$96\%$ cellulose, a linear $\beta$-$1,4$ glucan. Remaining components include pectins, waxes, proteins and mineral matter. Cotton crystallinity is roughly $65$–$70\%$, and it shows the Cellulose I crystal lattice.

6. What causes the natural convolutions (twists) in cotton fibre and how many per inch are typical?

   Convolutions arise from the collapse of the lumen and differential drying/spiralling of fibrils in the secondary wall as the fibre dries on maturing. Typical mature cotton has about $60$ convolutions per cm (around $150$ per inch); the twists aid spinning by interlocking fibres.

7. What is the chemical and morphological structure of wool fibre?

   Wool is a protein (keratin) fibre composed of $\alpha$-amino acids cross-linked by cystine (disulphide $\ce{-S-S-}$) bonds. Morphologically it has an outer cuticle of overlapping scales, a cortex (ortho- and para-cortex giving crimp), and sometimes a medulla in coarse fibres.

8. What is the significance of disulphide (cystine) crosslinks in wool?

   The cystine $\ce{-S-S-}$ crosslinks bind adjacent keratin chains, giving wool its insolubility, elastic recovery, resilience and set-retention. They can be broken by reducing agents and reformed (basis of permanent setting); their cleavage by alkali explains wool's poor alkali resistance.

9. What is the bilateral (ortho/para-cortex) structure of wool and what does it cause?

   The wool cortex is divided into orthocortex and paracortex arranged side by side (bilateral). The paracortex has higher sulphur (more crosslinks) and the two cortices have different swelling/contraction, producing the natural three-dimensional crimp of wool.

10. What is silk chemically, and what are its two main components?

    Silk is a protein fibre. Its two components are fibroin (the structural filament protein, $\approx 70$–$80\%$) and sericin (the gum that binds the two brins, $\approx 20$–$25\%$). Fibroin is rich in glycine, alanine and serine giving a $\beta$-pleated-sheet crystalline structure.

11. Describe the cross-section and filament structure of silk.

    Cultivated (mulberry) silk consists of two triangular fibroin filaments (brins) cemented together by sericin gum (bave). After degumming (boiling-off of sericin), the cross-section is a smooth, roughly triangular/rounded fibroin filament responsible for silk's lustre.

12. What are bast fibres? Give examples.

    Bast fibres are cellulosic fibres obtained from the phloem (inner bark/stem) of dicotyledonous plants, extracted by retting. Examples: jute, flax (linen), hemp, ramie and kenaf. They are multicellular fibre bundles bound by lignin and pectin.

13. What is retting in the context of bast fibre extraction?

    Retting is the controlled microbial or chemical degradation of the pectin and gummy substances binding the bast fibre bundles to the woody stem, allowing the fibres to be separated. Types include dew (field) retting, water retting, and chemical/enzymatic retting.

14. Compare the lignin content of jute and flax and its effect on properties.

    Jute contains high lignin ($\approx 12$–$14\%$), making it stiff, brittle, prone to yellowing and weakening on exposure. Flax has low lignin ($\approx 2\%$) and high cellulose, giving it greater strength, flexibility and durability (used for fine linen).

15. Give the broad classification of textile fibres into natural and man-made categories.

    Natural fibres: vegetable/cellulosic (cotton, flax, jute), animal/protein (wool, silk), and mineral (asbestos). Man-made fibres: regenerated/natural-polymer (viscose rayon, acetate), synthetic (nylon, polyester, acrylic, polypropylene), and inorganic (glass, carbon, metal).

16. What distinguishes a regenerated fibre from a synthetic fibre?

    A regenerated fibre is made by chemically dissolving a naturally occurring polymer (e.g., cellulose) and re-forming it into filaments (viscose rayon, acetate, lyocell). A synthetic fibre is built from small monomers polymerized synthetically (nylon, polyester, acrylic).

17. What raw material and process give carbon fibres, and at what temperatures?

    Carbon fibres are made mainly from polyacrylonitrile (PAN) precursor (also pitch/rayon) by: (1) stabilization/oxidation in air at $200$–$300\,^{\circ}\mathrm{C}$; (2) carbonization in inert atmosphere at $1000$–$1500\,^{\circ}\mathrm{C}$; (3) optional graphitization at $2000$–$3000\,^{\circ}\mathrm{C}$ for higher modulus.

18. State typical property values (modulus, density) that make carbon fibre a high-performance fibre.

    Carbon fibre has very high specific strength and stiffness: tensile modulus $\approx 200$–$600\ \mathrm{GPa}$, tensile strength $\approx 3$–$7\ \mathrm{GPa}$, low density $\approx 1.75$–$2.0\ \mathrm{g/cm^{3}}$, low thermal expansion and excellent chemical/thermal stability.

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