One question at a time. Build your Tamil Nadu HSE First Year Textile Technology understanding.
First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.
Continue in the practice tool above to load more questions, 50 at a time.
Jute is a bast fibre obtained from the stem of plants such as Corchorus species, and since it comes directly from a plant it is classed as a natural vegetable (cellulosic) fibre. Viscose rayon is a man-made regenerated fibre, nylon is fully synthetic, and silk is a natural animal fibre.
Cotton is a seed-hair fibre whose dry mass is roughly ninety per cent or more cellulose, so cellulose is its chief constituent. Keratin is the protein of wool and hair, fibroin is the protein of silk, and lignin is a major component of jute and other bast fibres.
The silk filament extruded by the silkworm consists of the fibrous protein fibroin, cemented together by the gum sericin. Keratin is the protein of wool and hair, casein is the milk protein used for regenerated protein fibre, and cellulose is a plant polysaccharide.
Wool has an outer layer of overlapping scales; when heat, water and mechanical agitation act together the scales interlock, so the fibres migrate in one direction and entangle, producing felting shrinkage. Wool is a protein fibre, so it does not dissolve in a normal wash liquor and it contains no cellulose.
Bast fibres are obtained from the phloem or soft bast layer of the plant stem, and jute, flax and hemp all belong to this group. Cotton is a seed-hair fibre and sisal is a leaf fibre, which is why neither of these is classed as a bast fibre.
In the viscose process the natural cellulose is converted into cellulose xanthate, dissolved and then coagulated back into filament form, so the existing polymer is regenerated rather than built up from monomers. Viscose is therefore neither a true synthetic fibre nor a natural filament drawn directly from a plant.
Poly(ethylene terephthalate) is a condensation polymer of ethylene glycol and terephthalic acid or its dimethyl ester, formed with the elimination of water or methanol. Caprolactam gives nylon 6, acrylonitrile gives acrylic fibre, and adipic acid with hexamethylene diamine gives nylon 6,6.
Thermoplastic fibres are made of linear polymers that soften on heating and harden again on cooling without chemical change, which is why they can be heat-set, pleated and texturised. Protein fibres such as wool and silk char and smell of burning hair, and none of these fibres decomposes in cold water.
Drawing straightens the long-chain molecules and aligns them parallel to the fibre axis, so an applied load is shared by many chain bonds and the yarn becomes stronger and less extensible. A lower degree of polymerisation would normally reduce strength, while surface scales and moisture content do not explain a difference in tenacity of this kind.
Moisture regain is expressed on the oven-dry mass, so regain equals the mass of water divided by the oven-dry mass, multiplied by one hundred: (1.5 divided by 8.5) multiplied by 100, which is about 17.6 per cent. The 15 per cent figure is the moisture content calculated on the original wet mass, which is a different quantity.
Cotton grows as a seed hair only a few centimetres long, so it is a staple fibre and must be twisted together with other fibres to make a yarn. Silk is extruded by the silkworm as a continuous filament, while nylon and polyester are manufactured fibres initially produced as continuous filaments.
By convention, moisture regain uses the oven-dry mass of the fibre as the denominator, so a fibre holding 8 g of water per 100 g dry fibre has a regain of 8%. Moisture content, by contrast, uses the total wet mass as the denominator, which is why the two values differ.
Elastic recovery measures how completely a fibre returns to its original length after a specified strain is removed. A fibre with high elastic recovery, such as wool or spandex, resists permanent deformation, whereas a low-recovery fibre remains extended.
The lumen is the hollow core of the cotton fibre, left when the protoplasm dries up at maturity. Around it lie the secondary wall of cellulose, the primary wall and the outer cuticle, while convolutions are the natural twists along the fibre.
The wool cuticle consists of flat, overlapping scales that give wool its directional friction effect and contribute to felting. Beneath it is the cortex, which forms the bulk of the fibre, and in coarse wools a central medulla may also be present.
The silkworm extrudes a pair of fibroin filaments coated with sericin, a gum that glues them into a single bave. Degumming removes the sericin to leave soft, lustrous silk filaments.
Cellulose acetate is dissolved in acetone and dry-spun: the solvent evaporates in warm air as the filament forms. Viscose rayon is wet-spun in a coagulating bath, while nylon 6,6 and polypropylene are melt-spun.
Cotton is cellulose, and cellulose burns like paper, giving a soft grey ash and a faint paper smell. Protein fibres such as wool smell of burnt hair, while nylon and polyester melt and form hard beads.
One gram-force per denier equals about 8.83 cN/tex, because the denier is nine times the tex and one gram-force is about 0.981 cN. Multiplying 3.5 by 8.83 gives approximately 30.9 cN/tex.
Nylon 6,6 is a polyamide made by condensing adipic acid with hexamethylenediamine. Acrylic is based on acrylonitrile, spandex is a polyurethane elastomer, and caprolactam is the monomer for nylon 6, not polyester.
Denier is defined as the mass in grams of 9,000 metres of fibre, so a 1-denier fibre weighs 1 g when its length is 9,000 m. The tex system uses 1,000 m, and decitex uses 10,000 m, so those lengths belong to different numbering systems.
The cortex is the thickest part of a wool fibre and consists of elongated cortical cells; its ortho- and para-cortex arrangement contributes to crimp and elasticity. The cuticle is the outer scale layer, the medulla is the central core in coarser fibres, and the epicuticle is the thin outer membrane of the scales.
Degumming removes sericin, the gum that cements the two fibroin filaments of raw silk, and leaves soft, lustrous silk. Retting separates bast fibres, carbonising removes vegetable matter from wool, and ginning separates cotton fibres from seeds.
As the cotton boll opens and the fibre dries, the cellulose layers collapse unevenly and the ribbon-like fibre develops convolutions. These convolutions help fibres to cling together during spinning but are not produced by ginning or scouring.
Retting is the microbial breakdown of pectin and other cementing substances that frees the bast fibre bundles from the stem. Reeling draws silk filaments, roving is a later spinning preparation, and carding opens and aligns fibres.
In acetylation, acetic anhydride reacts with hydroxyl groups on the cellulose chain, so the product is a cellulose ester. The acetyl groups are later partly removed in secondary acetate, but the polymer is still an ester rather than regenerated cellulose.
Elastane is built from soft polyurethane segments that extend under tension and hard segments that hold the structure together, giving high stretch and recovery. Polypropylene, nylon and polyester are not elastomeric fibres.
Covering power depends on the volume occupied by a given mass, so the lowest-density fibre gives the bulkiest, most covering structure. Polypropylene has a density of about 0.91 g/cm³, lower than cotton (about 1.52), wool (about 1.31) and polyester (about 1.38).
Water molecules enter the less ordered regions of viscose, break inter-chain hydrogen bonds and reduce the forces holding the chains together. Because viscose also has less orientation and crystallinity than cotton, this loosening causes a greater loss of wet strength.
Cuprammonium hydroxide (Schweizer's reagent) dissolves cellulose by disrupting hydrogen bonding between cellulose chains, so cotton gives a clear solution. Polyester, nylon and wool are not cellulose and do not dissolve in this reagent.
Cotton is composed mainly of cellulose, a polysaccharide built from glucose units. Keratin is the chief protein of wool and hair, while fibroin is the protein of silk filaments. Pectin occurs only as a minor non-cellulosic impurity in raw cotton.
Bast fibres are obtained from the stem of dicotyledonous plants, and flax is a well-known example used to produce linen. Cotton is a seed hair, whereas silk and wool are animal fibres.
One tex is defined as the mass in grams of 1,000 metres of fibre or yarn. The denier system uses 9,000 metres as its reference length. Tex therefore gives a direct measure of linear density in grams per kilometre.
Orientation aligns the strong covalent backbone of the polymer chains with the direction of applied load. This usually increases tensile strength and reduces extensibility because chain slippage is restricted. Orientation does not automatically raise moisture regain or lower fibre density.
In viscose production the cellulose xanthate solution is extruded into an acid coagulating bath, where the filament regenerates. Because coagulation occurs in a liquid bath, the process is classified as wet spinning. Dry spinning relies on solvent evaporation and melt spinning on cooling of a molten polymer.
Lyocell is produced by dissolving cellulose directly in N-methylmorpholine N-oxide, a solvent that can be recovered and recycled to a high degree. This avoids the xanthate route used for viscose rayon. Acetone is the solvent associated with cellulose acetate spinning.
Mercerization treats cotton with strong sodium hydroxide solution under tension, causing the fibre to swell and the lumen to collapse. This improves lustre, tensile strength and dye affinity. It does not convert cellulose into protein or make the fibre water-soluble.
Polyethylene terephthalate contains ester linkages and aromatic rings but lacks the abundant hydroxyl groups found in cellulose. Its high crystallinity also leaves little free space for water molecules to enter. These features together give polyester its low moisture regain.
The spinning limit expresses the minimum ratio of fibre length to fibre breadth needed for fibres to be drafted, overlapped and twisted into a coherent yarn. Fibres that are too short relative to their thickness tend to slip out during spinning. Moisture regain and crimp amplitude describe different fibre properties.
The tex system is based on 1,000 metres, while the denier system is based on 9,000 metres, so 1 tex equals 9 denier. Dividing 150 denier by 9 gives approximately 16.7 tex. This means the yarn has a mass of about 16.7 grams per 1,000 metres.
Ginning is the first mechanical step in cotton spinning: the gin grips the lint and pulls it past a grid that the seed cannot pass through, so fibre and seed are separated. Carding, combing and ring spinning all work on cotton that has already been ginned.
The blow-room sequence ends at the scutcher, which beats out the remaining trash, condenses the cotton into a uniform sheet and winds it as a lap for the cards. The lap is then the feed material for carding.
A card delivers a thick, untwisted rope of separated and partly parallelised fibres known as sliver, which is coiled into a can. Lap is the card's feed material, roving comes from the speed frame and a cop is the package formed on the ring frame.
In the indirect system, draft equals delivery hank divided by feed hank, so 1.4 divided by 0.14 gives 10. The material is drawn out to ten times its original length in the same time, and its weight per unit length falls to one tenth.
Combing grips the long fibres between a nipper and a comb while fine comb teeth rake out short fibres below a set length, together with neps and trash. It is placed after carding and before drawing whenever fine, strong yarns are required.
The traveller is a small C-shaped clip that rides on the ring flange and is dragged round by the yarn as the spindle rotates, so each revolution inserts one turn of twist and lays the yarn on the cop. The traveller lags slightly behind the spindle, and that speed difference is what winds the yarn.
For the indirect English system the twist multiplier is the turns per inch divided by the square root of the count: 20 divided by the square root of 40, that is 20 divided by 6.32, which gives about 3.16. The multiplier allows the twist hardness of yarns of different counts to be compared.
When several slivers are laid together, their random thick and thin places tend to cancel, so the combined sliver is more regular than any single feed sliver. The draft that follows reduces the count back to the required value, so evenness improves without loss of count control.
The roller setting must be a little longer than the effective length of the cotton so that the longest fibres are never gripped by both roller nips at the same moment. A shorter setting breaks or stretches fibres, while a much longer setting leaves the floating fibres uncontrolled in the drafting zone.
When the wire points of two surfaces oppose each other and the faster surface drags fibre past the slower one, tufts are opened into individual fibres and neps are loosened, which is carding action. Where the wire points face the same direction, material is simply transferred from one surface to the other, which is stripping.