Class 11 Textiles Technology — Exercise Solutions
Key Concepts Quick Recap
| Process | Input | Output | Key Equipment |
|---|
| Ginning | Seed cotton | Lint + seeds | Saw gin / Roller gin |
| Blow room | Baled cotton | Laps / Flock | Openers, blenders, scutcher |
| Carding | Lap | Card sliver | Carding machine (wire-covered rollers) |
| Combing | Card sliver | Combed sliver | Comber |
| Drawing | Multiple slivers | Drawn sliver | Drawing frame |
| Spinning | Roving | Yarn | Ring frame / Open-end spinning |
| Weaving | Warp + Weft yarns | Woven fabric | Loom (shuttle/shuttleless) |
| Dyeing | Grey fabric + dye | Coloured fabric | Jigger, pad-batch, jet dyeing |
I. Choose the Best Answer (MCQs)
1. The process of separating cotton lint from seeds is called: (a) Carding (b) Combing (c) Ginning (d) Drawing
Answer(c) Ginning Cotton ginning: Roller gin (Jacob's gin, 1840s): metal fingers + roller → gentle; preserves long staple (used for extra-long and long staple cotton). Saw gin (Eli Whitney, 1793): rotating saw-teeth pull fibres through a grid; faster; for shorter staple. Output: lint (fibre) and cotton seed (pressed for cottonseed oil and meal).
2. The purpose of carding in the textile process is to: (a) Dye the fibre (b) Open, clean, and align fibres; remove short fibres and neps (c) Twist fibres into yarn (d) Weave fibres into fabric
Answer(b) Open, clean, and align fibres; remove short fibres and neps Carding: fibres fed between wire-covered rollers at different speeds → fibres disentangled, aligned, short fibres separated, neps (tangled fibre knots) removed → card sliver (loose rope of parallel fibres). Carded yarn: contains some short fibres; lower quality. Combed yarn: further removal of short fibres → finer, smoother, stronger.
3. In weaving, the interlacing of warp and weft is controlled by: (a) Shuttle only (b) Reed (c) Healds/heddles (shafts) (d) Roller beam
Answer(c) Healds/heddles (shafts) Weaving mechanism: 1. Shedding: healds (heddle frames with wire eyes) separate alternate warp yarns → create shed (V-shaped opening). 2. Picking: weft yarn passed through shed (by shuttle, rapier, air jet, or water jet). 3. Beating: reed pushes each weft pick back against fell of cloth. These three motions repeat for every pick.
4. Which type of knitting produces tubular fabric? (a) Warp knitting (b) Weft knitting on circular machine (c) Weaving (d) Tatting
Answer(b) Weft knitting on circular machine Circular knitting machine: needles arranged in a cylinder → weft yarn fed and knitted in a continuous circle → produces seamless tubular fabric (for T-shirts, hosiery). Flat knitting: needles in a flat bed → flat fabric (for collars, full-fashioned knitwear). Warp knitting: yarns run lengthwise; used for lace, nets, sports fabrics.
5. Reactive dyes are most suitable for: (a) Wool (b) Polyester (c) Cotton and cellulosic fibres (d) Nylon
Answer(c) Cotton and cellulosic fibres Reactive dyes: form covalent bonds with −OH groups of cellulose fibres (cotton, linen, viscose) → excellent wash-fastness, bright colours. Dye classes by fibre: Disperse dyes → polyester. Acid dyes → wool, silk, nylon. Vat dyes → cotton (insoluble, reduced to soluble leuco form). Direct dyes → cotton (poor wash-fastness).
6. Mercerisation involves treating cotton with: (a) Sulphuric acid (b) Caustic soda (NaOH) under tension (c) Salt water (d) Bleaching powder
Answer(b) Caustic soda (NaOH) under tension Mercerisation (John Mercer, 1844): cotton yarn/fabric immersed in concentrated NaOH (18-25%) under tension → cotton swells → kidney-shaped cross-section becomes rounded → more reflective → increased lustre, strength (+10%), and dye affinity. Widely used for premium cotton shirting and sewing thread.
7. The tenacity of a textile fibre is measured as: (a) Elongation percentage (b) Breaking force per unit linear density (g/denier or cN/tex) (c) Moisture regain percentage (d) Twist per metre
Answer(b) Breaking force per unit linear density (g/denier or cN/tex) Tenacity: strength normalised to linear density (fibre fineness). Formula: Tenacity = Breaking strength (g) / Denier. High-tenacity fibres: Kevlar, carbon fibre, UHMWPE. Standard cotton: ~3-4 g/denier; Polyester: ~4-7 g/denier; Nylon: ~5-9 g/denier.
II. Short Answer Questions
Q1. Explain the difference between woven and knitted fabrics.
Answer
| Property | Woven | Knitted |
|---|
| Structure | Two sets of yarns (warp + weft) interlaced at right angles | Loops of yarn interlocked together |
| Stretchability | Low stretch (unless elastic yarn or bias cut) | High stretch (loops can open up) |
| Stability | High dimensional stability; minimal elongation | Less stable; can run (like a ladder in hosiery) |
| Comfort | Less conforming to body | High conformity to body shape |
| Applications | Shirts, trousers, sarees, suiting | T-shirts, sportswear, hosiery, socks |
| Strength | Generally stronger (due to interlacing) | Can be weaker; depends on structure |
| Breathability | Moderate (depends on weave density) | High (open loop structure allows air circulation) |
Q2. What are the pre-treatment processes applied to grey fabric before dyeing?
Answer
Grey (greige) fabric: fabric as it comes from the loom/knitting machine; contains impurities (natural waxes, seed fragments, sizing, oil, dust) that must be removed before dyeing.
Pre-treatment processes:
1. Singeing: Fabric passed over gas flame → burns off protruding fibres (fuzz) → smooth, even surface.
2. Desizing: Removes size (starch or synthetic sizing applied to warp yarns during weaving to prevent breakage). Methods: enzymatic (α-amylase for starch), oxidative, hydrolytic.
3. Scouring: Removes natural impurities (wax, pectins, seed fragments in cotton; lanolin in wool). Cotton: NaOH treatment (kier boiling or jet scouring). Wool: mild detergent (avoid felting).
4. Bleaching: Removes natural colour (yellowing of cotton from flavones). Chemical: H₂O₂ (hydrogen peroxide, preferred for cotton/wool), sodium hypochlorite (NaOCl, cotton only). Optical brightening agents (OBAs) for whiteness.
5. Mercerisation (cotton only): NaOH treatment under tension → lustre, strength, dye affinity.
Resultfabric is white, clean, absorbent, and ready for dyeing or printing.
Exam Checklist
- Ginning: cotton lint separated from seeds.
- Carding: aligns fibres, removes short fibres/neps → card sliver.
- Combing: further removes short fibres (noils) → finer combed yarn.
- Drawing → Roving → Ring spinning → Yarn.
- Weaving: shedding (healds) → picking (weft) → beating (reed).
- Reactive dyes: cotton (covalent bond). Disperse: polyester. Acid: wool/silk.
- Mercerisation: NaOH + tension → lustre + strength.
- Pre-treatment: Singe → Desize → Scour → Bleach → (Mercerise).
- Tenacity = breaking strength / linear density (g/denier).
