Which reagent is used to confirm acetate in a fibre sample?

Acetone, in which acetate dissolves

Boiling 5 per cent sodium hydroxide

Assertion (A): Denim shows diagonal lines on its face. Reason (R): The warp yarns of classic denim are dyed with indigo, a vat dye. Choose the correct option.

Both A and R are true, but R is not the correct explanation of A

Both A and R are true, and R is the correct explanation of A

Both A and R are true, but R is not the correct explanation of A

Which statements about knitted fabrics are correct? Select all that apply.

Interlock is a weft-knitted double-knit structure

In weft knits, courses are horizontal rows of loops and wales vertical columns

Interlock is a weft-knitted double-knit structure

In weft knits, courses are horizontal rows of loops and wales vertical columns

Warp knits ladder more easily than weft knits

The filtering middle layer of a three-ply surgical mask is typically made by which process?

Melt-blowing, a polymer-laid non-woven process

Textiles I: Textile Terminology, Classification and Identification of Fibres, Yarns and Weaves, Manufacture and Properties of Major Fibres, and Fabric Construction

Unit III takes three chapters here because each of its first nine items is a technical process in its own right, from fibre to finished and tested fabric. This first chapter covers items 1 to 3: the vocabulary of fibre, yarn, weave and fabric; how fibres, yarns and weaves are classified and identified in the laboratory; how the major natural and manufactured fibres are produced, with the properties that decide their end uses; and the three routes to fabric, weaving, knitting and non-woven bonding. The next chapter takes finishes, dyeing and printing and India's traditional textiles; the third takes testing, the environment, recent developments and the research-methods slice on types of research.

1. Terminology and the classification of fibres and yarns

A textile fibre is a unit of matter, very long in relation to its width, with enough strength, flexibility and cohesiveness to be spun into yarn. Short fibres measured in centimetres are staple fibres (cotton, wool, cut man-made fibre); continuous strands measured in metres or kilometres are filaments (silk, most man-made fibre as extruded). A yarn is a continuous strand of fibres or filaments suitable for making fabric; a fabric is a planar structure of yarns or fibres, made by weaving, knitting, felting, bonding, knotting or braiding.

Class	Sub-class	Examples
Natural	Cellulosic (plant)	Cotton (seed), flax or linen, jute, hemp, ramie (bast), coir (fruit), kapok
Natural	Protein (animal)	Wool, specialty hair (pashmina, mohair, angora), silk (mulberry, tasar, eri, muga)
Natural	Mineral	Asbestos (now largely banned for health reasons)
Manufactured	Regenerated and modified cellulose	Viscose rayon, modal, lyocell, cupro; acetate and triacetate
Manufactured	Synthetic	Polyamide (nylon 6 and 6,6), polyester, acrylic, modacrylic, polypropylene, elastane (spandex), aramids
Manufactured	Inorganic	Glass, carbon, metallic fibres

Yarns are spun (from staple) or filament, single or plied (two or more singles twisted together), and simple or novelty (slub, boucle, nub, chenille). Twist holds staple fibres together: a Z twist runs like the centre of the letter Z, an S twist the other way, and plied yarns are usually twisted opposite to their singles. Yarn fineness is expressed in two kinds of system. In direct systems, a higher number means a coarser yarn: tex is grams per 1,000 metres and denier grams per 9,000 metres, so denier = 9 × tex. In indirect systems, a higher number means a finer yarn: the English cotton count (Ne) is the number of 840-yard hanks weighing one pound.

🧠 Direct gets heavier, indirect gets finer

A 10-tex yarn weighs 10 g per 1,000 m, so 9,000 m weigh 90 g: 90 denier. A 60s cotton yarn is finer than a 20s. If a question compares yarns across systems, first decide which way the numbers run.

2. Identification of fibres and weaves

Fibre group	Burning test	Microscope (longitudinal view)
Cotton, linen, viscose	Burns quickly with a yellow flame, smell of burning paper, soft grey ash, afterglow	Cotton: flat twisted ribbon with convolutions; linen: bamboo-like nodes; viscose: lengthwise striations
Wool, silk	Burns slowly, curls from the flame, self-extinguishing, smell of burning hair or feathers, crushable black ash	Wool: overlapping surface scales; silk: smooth, fine, structureless rod
Nylon, polyester, acrylic	Melt and shrink from the flame, drip, leave a hard bead; polyester smokes and smells sweetish, nylon smells of celery, acrylic burns with an acrid smell	Smooth even rods, round unless deliberately shaped (trilobal)
Acetate	Melts and burns, vinegar smell, hard black bead	Smooth with a few striations

Solubility confirms what burning suggests: acetate dissolves in acetone, nylon in formic acid, wool and silk in boiling 5 per cent sodium hydroxide, and cellulosic fibres in concentrated sulphuric acid. Protein fibres are damaged by alkali; cellulosic fibres by acid.
Weaves are identified with a pick glass by following the interlacing: plain weave interlaces one over one under; twill shows diagonal wales; satin shows long floats on the face and a smooth, lustrous surface.

⚠️ A blend confuses the burning test

A polyester-cotton blend both chars like cotton and forms beads like polyester, and the result depends on the ratio. Burning is a screening test; microscopy and solubility are needed to identify blends, and quantitative analysis dissolves out one component and weighs the residue.

3. Manufacture, properties and end uses of major fibres

Cotton: picked bolls are ginned to separate lint from seed; in the mill the fibre is opened and cleaned (blowroom), carded into a sliver, combed for fine yarns, drawn, made into roving and spun, usually on ring frames or open-end rotors.
Wool: shorn fleece is sorted, scoured to remove grease (lanolin) and suint, carbonised to remove burrs, then carded for woollen yarns or carded and combed for smoother worsted yarns.
Silk: in sericulture the silkworm (Bombyx mori for mulberry silk) spins a cocoon of two filaments (fibroin) glued by sericin; cocoons are stifled, filaments reeled, and sericin removed by degumming, which gives silk its lustre and soft handle. India produces all four commercial silks, with golden muga found only in Assam.
Linen: flax stems are retted (rotted to free the bast fibre), broken, scutched and hackled before spinning.
Viscose: wood pulp is steeped in sodium hydroxide, aged, treated with carbon disulphide to form cellulose xanthate, dissolved in dilute alkali, ripened and extruded through spinnerets into a sulphuric acid bath (wet spinning). Lyocell dissolves cellulose directly in the recyclable solvent N-methylmorpholine N-oxide in a closed loop.
Synthetics are polymerised and then spun: nylon and polyester by melt spinning (nylon 6,6 from hexamethylene diamine and adipic acid, nylon 6 from caprolactam, polyester from ethylene glycol and terephthalic acid), acrylic by wet or dry spinning, acetate and spandex by dry spinning. Filaments are drawn to orient the molecules and may be textured for bulk or cut into staple.

Moisture regain is the moisture in a fibre as a percentage of its oven-dry weight at standard conditions; it explains comfort, static and drying time
Fibre	Approximate moisture regain (per cent)	Distinctive properties	Typical end uses
Cotton	8.5	Absorbent, comfortable, stronger wet than dry, creases, withstands alkali and hot washing	Summer wear, towels, bed linen, denim
Wool	About 14 to 16	Highest regain, warm, resilient, felts with heat, moisture and agitation, weak when wet, harmed by alkali	Winter wear, suiting, carpets, blankets
Silk	About 11	Lustrous, strong for its fineness, drapes well, sensitive to light and perspiration	Saris, formal wear, scarves
Viscose	About 11 to 13	Absorbent, soft, drapes well, weak when wet	Dress material, linings
Nylon	About 4	Very strong, elastic, abrasion-resistant, thermoplastic	Hosiery, ropes, swimwear, luggage
Polyester	About 0.4	Strong, crease-resistant, quick-drying, heat-settable, oleophilic, builds static	Blends with cotton and viscose, sportswear, fibrefill
Acrylic	About 1.5	Wool-like bulk and warmth, light, resistant to sunlight and moths	Sweaters, blankets, outdoor fabrics

4. Fabric construction: woven, knitted and non-woven

Weaving interlaces two sets of yarns at right angles: the lengthwise warp (ends) and the crosswise weft (picks, filling). A loom performs three primary motions, shedding (raising some warp ends to open a passage), picking (passing the weft through the shed) and beating-up (pushing the pick into the cloth), with let-off and take-up as secondary motions. Shuttle looms have largely given way to shuttleless looms, projectile, rapier, air-jet and water-jet, the last suited only to hydrophobic filament yarns. The selvedge is the self-finished edge that runs parallel to the warp.

Weave	Structure	Examples
Plain and its derivatives	One over one under; rib and basket (matt) variations	Muslin, poplin, cambric; oxford (basket)
Twill	Interlacings step to form diagonal wales; strong, drapes well, hides soil	Denim (warp-faced 3/1), gabardine, drill, serge
Satin and sateen	Long floats with scattered interlacings; lustrous, smooth, snags easily	Satin (warp floats), sateen (weft floats)
Fancy weaves	Dobby (small geometric figures), jacquard (large figures, each warp end controlled individually), pile, leno, double cloth	Brocades (jacquard), velvet (warp pile), corduroy and velveteen (weft pile), terry towelling (uncut loops), mosquito netting (leno)

Knitting builds fabric from interlocking loops. In weft knitting one yarn runs across the fabric forming courses (horizontal rows of loops) and wales (vertical columns): single jersey (plain), rib, purl and interlock are the basic structures, and the knit, tuck and miss stitches vary them. Weft knits stretch and fit well but can ladder when a loop breaks. In warp knitting, many yarns run lengthwise, each forming loops in adjacent wales; tricot and raschel are warp knits, more stable and run-resistant. Non-woven fabrics skip yarn altogether: a web of fibres is formed dry-laid (carded or air-laid), wet-laid (like paper) or polymer-laid (spunbond, melt-blown) and then bonded mechanically (needle-punching, hydroentanglement), thermally or chemically. Spunbond-meltblown-spunbond laminates are the filtering layers of surgical masks; other non-wovens serve as wipes, diapers, interlinings and geotextiles. Felt, the oldest non-woven, relies on the scales of wool locking under heat, moisture and pressure.

🎯 Why jersey stretches and poplin does not

A loop can straighten and recover, so knits stretch in both directions (most along the course). Woven yarns cross straight at right angles and stretch little along warp or weft; the only give is on the bias, at 45 degrees, which is why bias-cut garments drape and cling.

Key takeaways

Fibres are natural (cellulosic, protein, mineral) or manufactured (regenerated cellulosic, synthetic, inorganic); staple is short, filament continuous.
Tex and denier are direct systems (denier = 9 × tex); the cotton count is indirect, so a higher count is finer.
Cellulosics burn like paper, protein fibres smell of burning hair and leave crushable ash, and thermoplastic synthetics melt into hard beads; solubility confirms the result.
Viscose is made by the xanthate route and wet spun; nylon and polyester are melt spun; wool has the highest and polyester one of the lowest moisture regains.
Weaving uses shedding, picking and beating-up; the basic weaves are plain, twill and satin; knits are weft (courses and wales, can ladder) or warp (tricot, raschel); non-wovens are webs bonded mechanically, thermally or chemically.

Practice questions (10)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

A 1,000-metre length of yarn weighs 10 grams. What is its count in denier? Type the number.
Numerical answer — type the value.
Show answer
Answer: 90
10 g per 1,000 m is 10 tex. Denier is grams per 9,000 m, so 9 × 10 = 90 denier. Both are direct systems, in which a larger number means a heavier, coarser yarn.
A fibre burns slowly, shrinks from the flame, smells of burning hair and leaves a black ash that crushes easily. It is most likely:
1. Viscose
2. Cotton
3. Polyester
4. Wool
Show answer
Answer: D — Wool
The smell of burning hair and crushable ash mark a protein fibre such as wool or silk. Cotton and viscose smell of burning paper with soft grey ash, and polyester melts into a hard bead that cannot be crushed.
Under the microscope a fibre appears as a flat, twisted ribbon with convolutions and a kidney-shaped cross-section. The fibre is:
1. Wool
2. Silk
3. Cotton
4. Linen
Show answer
Answer: C — Cotton
Convolutions and a bean- or kidney-shaped cross-section are the signature of mature cotton. Linen shows bamboo-like cross-markings, wool overlapping scales, and silk a smooth rod with a roughly triangular cross-section.
Which of the following fibres are made by melt spinning? Select all that apply.
1. Polyester
2. Acrylic
3. Nylon
4. Viscose rayon
Show answer
Answer: A — Polyester; C — Nylon
Nylon and polyester melt without decomposing and are extruded from the melt. Acrylic degrades before it melts, so it is wet or dry spun from solution, and viscose is wet spun: cellulose xanthate solution is extruded into a sulphuric acid bath, because cellulose decomposes rather than melts.
Which reagent is used to confirm acetate in a fibre sample?
1. Acetone, in which acetate dissolves
2. Dilute acetic acid
3. Boiling 5 per cent sodium hydroxide
4. Cold water
Show answer
Answer: A — Acetone, in which acetate dissolves
Acetate is the fibre that dissolves in acetone, which also explains why nail polish remover damages acetate garments. Boiling 5 per cent sodium hydroxide dissolves protein fibres such as wool and silk.
Assertion (A): Denim shows diagonal lines on its face. Reason (R): The warp yarns of classic denim are dyed with indigo, a vat dye. Choose the correct option.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true, but R is false
4. A is false, but R is true
Show answer
Answer: B — Both A and R are true, but R is not the correct explanation of A
Both are true, but R does not explain A. The diagonal wale comes from the twill weave, in which each interlacing steps over by one end on the next pick; indigo dyeing of the warp explains denim's colour and its characteristic fading, not the diagonal.
Which statements about knitted fabrics are correct? Select all that apply.
1. Tricot is a warp knit
2. Interlock is a weft-knitted double-knit structure
3. In weft knits, courses are horizontal rows of loops and wales vertical columns
4. Warp knits ladder more easily than weft knits
Show answer
Answer: A — Tricot is a warp knit; B — Interlock is a weft-knitted double-knit structure; C — In weft knits, courses are horizontal rows of loops and wales vertical columns
Courses and wales, tricot as a warp knit, and interlock as a weft double knit are all correct. It is weft knits that ladder when a loop breaks; warp knits, with their lengthwise yarns looping into adjacent wales, resist running.
The filtering middle layer of a three-ply surgical mask is typically made by which process?
1. Felting of wool
2. Weft knitting
3. Leno weaving
4. Melt-blowing, a polymer-laid non-woven process
Show answer
Answer: D — Melt-blowing, a polymer-laid non-woven process
Melt-blowing draws molten polypropylene into microfibres with hot air, forming a fine web that traps particles; it is usually sandwiched between spunbond layers (SMS). Knits, leno weaves and felts are far too open or bulky for this filtration.
Which fibre has the highest moisture regain under standard conditions?
1. Polyester
2. Wool
3. Cotton
4. Nylon
Show answer
Answer: B — Wool
Wool absorbs about 14 to 16 per cent of its dry weight, the highest of the common fibres, which helps it feel warm and not clammy. Cotton regains about 8.5, nylon about 4 and polyester only about 0.4 per cent.
Which of the following are primary motions of a loom? Select all that apply.
1. Beating-up
2. Shedding
3. Take-up
4. Picking
Show answer
Answer: A — Beating-up; B — Shedding; D — Picking
Shedding, picking and beating-up are the three primary motions without which no weaving happens. Take-up, which winds the woven cloth, and let-off, which releases warp, are secondary motions.