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Maharashtra HSC Textiles study materials
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Maharashtra HSC Textiles practice questions

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Question 1Textile Fibres: Classification, Properties and Identification

Which of the following fibres is obtained from a plant source and is therefore classified as a natural cellulosic fibre?

  1. Cotton Correct answer.
  2. Silk
  3. Wool
  4. Nylon

Explanation

Natural fibres are grouped by their chemical origin. Cotton is a seed hair made almost entirely of cellulose, so it belongs to the natural cellulosic group, while wool and silk are protein fibres and nylon is manufactured.

Question 2Textile Fibres: Classification, Properties and Identification

Silk is best described as which type of fibre?

  1. Synthetic polyester fibre
  2. Natural cellulosic fibre of vegetable origin
  3. Natural protein fibre of animal origin Correct answer.
  4. Regenerated cellulosic fibre

Explanation

Silk is secreted by the silkworm as a continuous filament and consists mainly of the protein fibroin. Because it comes from an animal, it is classed as a natural animal (protein) fibre.

Question 3Textile Fibres: Classification, Properties and Identification

Viscose rayon is classified as a man-made fibre because it is produced by dissolving and regenerating cellulose. Which raw material is the usual source of that cellulose?

  1. Wood pulp Correct answer.
  2. Petroleum
  3. Natural rubber latex
  4. Coal tar

Explanation

Regenerated cellulosic fibres start from purified cellulose, most often obtained from wood pulp. The cellulose is converted into a soluble compound, extruded, and then regenerated as filament, which makes the fibre man-made though plant-derived.

Question 4Textile Fibres: Classification, Properties and Identification

When a sample of cotton is burnt in a flame, which combination of smell and ash is observed?

  1. Smell of burning hair with dark crushable beads
  2. Smell of burning rubber with no residue
  3. Smell of vinegar with hard black beads
  4. Smell of burning paper with light grey fluffy ash Correct answer.

Explanation

Cotton is cellulosic, so it burns rapidly like paper and leaves a soft, light grey ash. The absence of a nitrogen or sulphur odour distinguishes it from protein and synthetic fibres.

Question 5Textile Fibres: Classification, Properties and Identification

Which reagent gives a characteristic red-violet colour with wool but does not produce that colour with cotton?

  1. Sodium chloride solution
  2. Benedict's solution
  3. Millon's reagent Correct answer.
  4. Iodine solution

Explanation

Millon's reagent reacts with the tyrosine residues in protein fibres, giving a red-violet colour with wool and silk. Cotton lacks these phenolic amino acid groups, so it does not respond in the same way.

Question 6Textile Fibres: Classification, Properties and Identification

A yarn sample dissolves completely in cold concentrated sulphuric acid at room temperature. Which fibre is most likely present?

  1. Nylon Correct answer.
  2. Wool
  3. Polyester
  4. Cotton

Explanation

Polyamides such as nylon are hydrolysed and dissolve in cold concentrated sulphuric acid. Cotton and wool are attacked only slowly or under stronger conditions, and polyester resists cold acid, so rapid dissolution identifies a polyamide.

Question 7Textile Fibres: Classification, Properties and Identification

Which property of wool is chiefly responsible for its good warmth and resilience in winter garments?

  1. Low moisture regain and high density
  2. Continuous filament with no crimp
  3. High crystallinity and smooth surface
  4. Crimped, scaly fibres that trap air Correct answer.

Explanation

Wool fibres are naturally crimped and covered with overlapping scales, so a wool yarn entraps many pockets of still air. Trapped air insulates, giving wool its warmth, and the crimp also contributes elasticity and resilience.

Question 8Textile Fibres: Classification, Properties and Identification

Which fibre is composed mainly of the polymer cellulose and therefore shows high moisture regain and good resistance to dilute alkalis?

  1. Cotton Correct answer.
  2. Acrylic
  3. Nylon
  4. Wool

Explanation

Cotton is roughly ninety per cent cellulose, and the many hydroxyl groups along the chain attract water, giving high moisture regain. Cellulose is also stable in dilute alkali, which is why cotton can be mercerised.

Question 9Textile Fibres: Classification, Properties and Identification

A fabric is labelled as polyester. Which property best explains why polyester garments dry quickly after washing?

  1. Rapid absorption through surface scales
  2. Strong swelling of the fibre in water
  3. Low moisture regain because the fibre is hydrophobic Correct answer.
  4. High moisture regain because of many hydroxyl groups

Explanation

Polyester is a hydrophobic synthetic polymer with very few water-attracting groups, so its moisture regain is low. Water therefore stays mainly on the surface and evaporates quickly, giving short drying times.

Question 10Textile Fibres: Classification, Properties and Identification

Under a microscope, a cotton fibre is recognised by which appearance?

  1. Triangular cross-section with sharp edges
  2. Smooth cylindrical rod with no markings
  3. Flattened, ribbon-like shape with twists Correct answer.
  4. Coarse stiff rod with a central lumen and no twists

Explanation

Mature cotton is a collapsed, ribbon-like tube with characteristic convolutions or twists along its length. These twists are a key identification feature under the microscope and distinguish cotton from smooth synthetic filaments.

Question 11Textile Fibres: Classification, Properties and Identification

Which of these fibres is a regenerated protein fibre rather than a regenerated cellulosic fibre?

  1. Viscose
  2. Azlon Correct answer.
  3. Acetate
  4. Modal

Explanation

Azlon is produced by dissolving and re-forming protein material such as casein or soya, so it belongs to the regenerated protein group. Viscose, acetate and modal all derive from cellulose and are regenerated cellulosic fibres.

Question 12Textile Fibres: Classification, Properties and Identification

A manufacturer wants a fibre that is strong, elastic and resistant to creasing for a wash-and-wear shirt. Which fibre property combination supports polyester for this use?

  1. High flammability with low elasticity
  2. High moisture regain with low tenacity
  3. High density with poor abrasion resistance
  4. High tenacity with good elastic recovery Correct answer.

Explanation

Polyester has high tensile strength and excellent elastic recovery, so it resists stretching and recovers from creasing. These properties keep a shirt looking smooth after washing, which is why polyester is chosen for wash-and-wear fabrics.

Question 13Textile Fibres: Classification, Properties and Identification

Which test would most reliably distinguish silk from wool in a laboratory?

  1. Measuring length of the sample
  2. Feeling the fabric by hand
  3. Burning test alone
  4. Solubility in cold concentrated hydrochloric acid Correct answer.

Explanation

Both silk and wool are protein fibres and give a similar burning-hair smell, so the burning test alone is unreliable. Silk dissolves readily in cold concentrated hydrochloric acid, whereas wool is much less affected, giving a clear distinction.

Question 14Textile Fibres: Classification, Properties and Identification

A fabric sample gives a blue colour with the iodine-sulphuric acid reagent. Which fibre is indicated?

  1. Nylon
  2. Cotton Correct answer.
  3. Wool
  4. Polyester

Explanation

Cellulosic fibres such as cotton give a blue colour with iodine in sulphuric acid because the reagent reacts with cellulose. Protein and synthetic fibres give different colours or no such response, so blue indicates a cellulosic fibre.

Question 15Textile Fibres: Classification, Properties and Identification

Which property of viscose rayon explains why it is often blended with polyester in suiting fabrics?

  1. Excellent elasticity that resists stretching
  2. Very low flammability
  3. Very high wet strength that aids washing
  4. High moisture absorbency that improves comfort Correct answer.

Explanation

Viscose has high moisture regain, so it absorbs perspiration and improves comfort, but it has low wet strength and poor elasticity. Blending it with strong polyester balances comfort with durability and shape retention.

Question 16Textile Fibres: Classification, Properties and Identification

Which fibre property makes nylon suitable for ropes and parachutes?

  1. Low strength with high moisture regain
  2. High density with low abrasion resistance
  3. High flammability with poor resilience
  4. High tensile strength with good elastic recovery Correct answer.

Explanation

Nylon is a polyamide with high tenacity and strong elastic recovery, so it withstands heavy loads and returns to shape after stretching. These qualities make it suitable for ropes and parachute fabrics.

Question 17Textile Fibres: Classification, Properties and Identification

Which statement correctly pairs a fibre with its chemical nature?

  1. Polyester - protein
  2. Viscose - polyamide
  3. Acrylic - polyacrylonitrile Correct answer.
  4. Wool - cellulose

Explanation

Acrylic fibres are made from polyacrylonitrile, a synthetic polymer. The other pairings confuse the chemical families: viscose is regenerated cellulose, wool is protein, and polyester is a synthetic ester polymer.

Question 18Textile Fibres: Classification, Properties and Identification

A fabric burns with a sputtering flame, gives a smell of burning rubber and leaves no ash. Which fibre is most consistent with these observations?

  1. Cotton
  2. Elastane Correct answer.
  3. Wool
  4. Viscose

Explanation

Elastomeric fibres such as elastane burn with sputtering and a rubber-like odour and leave little or no ash. Cellulosic fibres burn like paper and leave ash, while protein fibres smell of burning hair.

Question 19Textile Fibres: Classification, Properties and Identification

Which structural feature gives wool its characteristic felting behaviour?

  1. Highly crystalline flat ribbon shape
  2. Smooth continuous filament surface
  3. Overlapping surface scales that interlock Correct answer.
  4. Uniform circular cross-section with no scales

Explanation

Wool fibres carry overlapping scales that point towards the tip, so under moisture, heat and friction they can ratchet past each other and lock together. This directional friction is what causes felting and shrinkage.

Question 20Textile Fibres: Classification, Properties and Identification

A fabric suspected of being pure cotton is treated with dilute sodium hydroxide solution and then examined. Which observation supports the presence of cotton?

  1. The fibre melts into a hard bead
  2. The fibre gives a strong burning-hair odour
  3. The fibre swells and becomes smoother, indicating mercerisation Correct answer.
  4. The fibre dissolves completely and leaves no residue

Explanation

Cellulose resists dilute alkali, and cotton treated with sodium hydroxide swells, becomes rounder and takes on a smoother, more lustrous surface, a process called mercerisation. Dissolution, melting or a burning-hair smell would point to other fibre groups.

Question 21Textile Fibres: Classification, Properties and Identification

Which property of acrylic fibres makes them a common substitute for wool in knitwear?

  1. Rapid absorption and swelling in water
  2. Light weight, warmth and resistance to moths Correct answer.
  3. High moisture regain and easy felting
  4. High density and poor colour retention

Explanation

Acrylic is a lightweight synthetic that traps air well, giving warmth, and it is not attacked by moth larvae that damage wool. It also holds colour well, so it serves as a wool-like fibre in knitwear.

Question 22Textile Fibres: Classification, Properties and Identification

Which of the following fibres is a natural cellulosic fibre obtained from the stem of a plant?

  1. Viscose
  2. Silk
  3. Jute Correct answer.
  4. Cotton

Explanation

Jute is a bast fibre taken from the stem of the jute plant, and its main chemical constituent is cellulose. Cotton is also cellulosic but comes from the seed hair, while silk is protein and viscose is man-made.

Question 23Textile Fibres: Classification, Properties and Identification

Two white fabrics are supplied, one of wool and one of polyester. Which simple sequence most efficiently separates them in a school laboratory?

  1. Measure the length of each fabric
  2. Soak both in plain water and compare colour
  3. Weigh each fabric and compare masses
  4. Burn a yarn of each and compare odour and residue Correct answer.

Explanation

Burning a small yarn is quick and safe if done carefully, and the two fibres differ clearly: wool smells of burning hair and leaves crushable beads, while polyester melts, shrinks away from the flame and leaves a hard bead. Mass, length and plain water give no reliable chemical distinction.

Question 24Textile Fibres: Classification, Properties and Identification

Which fibre is most likely to shrink markedly when washed in hot water and dried in a tumble dryer?

  1. Acrylic
  2. Nylon
  3. Wool Correct answer.
  4. Polyester

Explanation

Wool felts and shrinks under heat, moisture and mechanical action because its scales interlock, and it also relaxes its natural crimp. Thermoplastic synthetics may soften but do not felt in the same way.

Question 25Textile Fibres: Classification, Properties and Identification

A fibre identification report states that the sample dissolves in a mixture of phenol and tetrachloroethane but not in cold concentrated sulphuric acid. Which fibre is indicated?

  1. Viscose
  2. Wool
  3. Cotton
  4. Polyester Correct answer.

Explanation

Polyester is soluble in hot phenol or phenol-tetrachloroethane mixtures yet resists cold concentrated sulphuric acid. Cellulosic and protein fibres behave differently in these reagents, so this solubility pattern identifies a polyester.

Question 26Textile Fibres: Classification, Properties and Identification

In the standard classification of textile fibres, to which group does jute belong?

  1. Regenerated cellulosic fibre
  2. Natural animal fibre
  3. Synthetic fibre
  4. Natural vegetable fibre Correct answer.

Explanation

Jute is obtained from the stem of a plant, so it is a natural fibre of vegetable origin and chemically consists mainly of cellulose. Animal fibres such as wool and silk are protein-based, while regenerated and synthetic fibres are man-made. This places jute firmly in the natural vegetable (bast) group.

Question 27Textile Fibres: Classification, Properties and Identification

A fibre is described as thermoplastic. Which behaviour follows directly from this property?

  1. It softens on heating and can be heat-set into a permanent shape Correct answer.
  2. It burns with the smell of burning hair
  3. It is attacked readily by dilute acids
  4. It absorbs a large amount of moisture from the air

Explanation

Thermoplastic fibres are linear polymers that soften when heated and harden again on cooling, so they can be shaped and heat-set. This is the basis of permanent pleating and texturising of polyester and nylon. Moisture absorption, burning smell and acid attack are separate properties not implied by thermoplasticity.

Question 28Textile Fibres: Classification, Properties and Identification

A fabric sample is mounted for microscopic examination and shows a smooth, glassy, rod-like appearance with no natural convolutions or scales. Which conclusion is most reasonable?

  1. It is probably wool, because scales lie flat under the microscope
  2. It is probably cotton, because convolutions are not always visible
  3. It is probably silk, because silk always shows a triangular cross-section
  4. It is probably a man-made filament fibre such as nylon or polyester Correct answer.

Explanation

Man-made filament fibres are extruded through spinnerets, so in longitudinal view they appear smooth and rod-like without the convolutions of cotton or the scales of wool. Cotton shows ribbon-like convolutions and wool shows overlapping scales. Silk can show smooth filaments, but the claim that it always shows a triangular cross-section is incorrect, since that shape is seen only in some silk and is a cross-sectional feature.

Question 29Textile Fibres: Classification, Properties and Identification

A blended shirting fabric is to be identified. A small sample is treated with cold concentrated sulphuric acid and the whole sample dissolves. Which interpretation is most consistent?

  1. The blend contains nylon, which dissolves in cold concentrated sulphuric acid Correct answer.
  2. The blend is cotton with viscose, both of which dissolve in this reagent
  3. The result is inconclusive because blends never dissolve completely
  4. The blend is wool with silk, both of which dissolve in this reagent

Explanation

Nylon is soluble in cold concentrated sulphuric acid, whereas polyester and cotton resist it under these conditions. Complete dissolution of the whole sample therefore points to a fibre such as nylon being present throughout. Cotton and viscose do not both dissolve in cold concentrated acid, and protein fibres swell or dissolve in other reagents rather than behaving as described.

Question 30Textile Fibres: Classification, Properties and Identification

A manufacturer needs a fibre for conveyor belting that must carry heavy loads with minimum stretch under tension. Comparing the load-extension behaviour of the candidate fibres, which choice is best justified?

  1. Polypropylene, because its low density reduces the belt weight
  2. Polyester, because its high initial modulus means it extends little before breaking Correct answer.
  3. Acrylic, because its soft handle cushions the load
  4. Nylon, because its high extensibility allows it to stretch and absorb the load

Explanation

A high initial modulus means the fibre resists extension at low loads, so the belt deforms little under tension and the drive length stays stable. Nylon is strong but has high extensibility, so it stretches noticeably before taking up the full load. Low density and soft handle affect weight and comfort but do not control stretch under tension.

Question 31Yarn Manufacture and Yarn Properties

In cotton yarn manufacture, which sequence correctly orders the operations that convert fibre to finished yarn?

  1. Blow room → Carding → Drawing → Spinning Correct answer.
  2. Carding → Spinning → Drawing → Combing
  3. Drawing → Blow room → Carding → Spinning
  4. Combing → Blow room → Drawing → Spinning

Explanation

The standard short-staple cotton sequence opens and cleans the fibre in the blow room, individualises it into a card sliver, levels and blends slivers on the draw frame, and finally attenuates and twists the roving into yarn on the ring frame. Combing is inserted after carding only for finer yarns, so it cannot precede the blow room.

Question 32Yarn Manufacture and Yarn Properties

In the cotton spinning sequence, the main purpose of the draw frame is to:

  1. Parallelise and blend slivers while improving evenness Correct answer.
  2. Convert sliver into a fine twisted yarn directly
  3. Remove seed and trash from the opened fibre
  4. Insert twist into the strand so it can be wound

Explanation

Doubling several card slivers and drafting them on the draw frame improves fibre parallelisation and regularity through the doubling effect, which reduces random irregularity. Twist insertion and final attenuation belong to the ring frame, while trash removal belongs to the blow room.

Question 33Yarn Manufacture and Yarn Properties

A yarn is described as 30 tex. This value tells the spinner that the yarn has:

  1. A breaking strength of 30 grams per tex
  2. A mass of 30 grams per 1000 metres of yarn Correct answer.
  3. A length of 30 metres per gram of yarn
  4. A twist of 30 turns per metre

Explanation

Tex is a direct linear density system defined as the mass in grams of 1000 metres of yarn. Therefore 30 tex means 1000 m of that yarn weighs 30 g. Twist level and tenacity are separate properties and are not expressed by the tex number.

Question 34Yarn Manufacture and Yarn Properties

Two yarns are compared. Yarn A has a count of 40 tex and Yarn B has a count of 20 tex. Which statement is correct?

  1. Yarn A is finer than Yarn B
  2. Yarn B is coarser because its number is larger in an indirect count
  3. Yarn A is coarser than Yarn B Correct answer.
  4. Both yarns have the same linear density

Explanation

Tex is a direct system, so a larger tex value means a heavier, coarser yarn. Since 40 tex is greater than 20 tex, Yarn A is the coarser of the two. The reasoning that a larger number means finer applies only to indirect count systems such as cotton count.

Question 35Yarn Manufacture and Yarn Properties

A yarn of 24 tex is required, but the spinning mill's count is given as 25 English cotton count. What is the approximate tex value of the mill's yarn?

  1. 25 tex
  2. 59 tex
  3. 10.6 tex
  4. 23.6 tex Correct answer.

Explanation

The conversion is tex = 590.5 ÷ English cotton count for the indirect cotton system. Dividing 590.5 by 25 gives approximately 23.6 tex, which is close to but not exactly the required 24 tex. The other values come from using the wrong conversion constant or inverting the formula.

Question 36Yarn Manufacture and Yarn Properties

In a direct yarn numbering system, the yarn number is:

  1. Independent of the mass per unit length
  2. Directly proportional to the mass per unit length Correct answer.
  3. Inversely proportional to the mass per unit length
  4. Directly proportional to the length per unit mass

Explanation

Direct systems such as tex and denier fix a unit length and express the mass of that length. A heavier yarn of the same length therefore carries a larger number, so the number rises with mass per unit length. Indirect systems behave in the opposite way.

Question 37Yarn Manufacture and Yarn Properties

A yarn sample of 100 metres has a mass of 2.5 grams. What is its linear density in tex?

  1. 25 tex Correct answer.
  2. 0.025 tex
  3. 250 tex
  4. 40 tex

Explanation

Tex is the mass in grams of 1000 metres. Scaling 2.5 g per 100 m to a 1000 m basis gives 2.5 × 10 = 25 tex. Dividing instead of multiplying or misplacing the decimal produces the other values.

Question 38Yarn Manufacture and Yarn Properties

Twist multiplier is preferred over twist per inch when comparing yarns of different counts because it:

  1. Removes the effect of yarn linear density, giving a twist factor related to yarn diameter Correct answer.
  2. Determines the breaking strength of the yarn directly
  3. Specifies the fibre length used in the yarn
  4. Measures the actual number of turns inserted per metre of yarn

Explanation

Twist multiplier relates twist to the square root of the count, so it normalises twist for yarn thickness and reflects the twist angle at the yarn surface. Two yarns of different counts with the same twist multiplier have similar surface twist angles and therefore comparable handle and character.

Question 39Yarn Manufacture and Yarn Properties

A single yarn is made with twist in the S direction. Which description matches S twist?

  1. The yarn is a plied yarn twisted in the opposite direction to its components
  2. The visible helix follows the diagonal of the letter S when the yarn is held vertically Correct answer.
  3. The fibres are parallel with no twist at all
  4. The visible helix follows the diagonal of the letter Z when the yarn is held vertically

Explanation

Twist direction is named by the slant of the surface fibres: in S twist the helix runs like the middle stroke of the letter S. Z twist gives the opposite slant. The direction is a naming convention and is independent of whether the yarn is single or plied.

Question 40Yarn Manufacture and Yarn Properties

For a given yarn count, increasing the twist level beyond the optimum generally causes tenacity to:

  1. Rise continuously without limit
  2. Rise to a maximum and then fall Correct answer.
  3. Fall continuously from the start
  4. Remain completely unchanged

Explanation

Increasing twist first improves fibre gripping and lateral pressure, raising strength up to an optimum. Beyond that optimum the fibres become increasingly inclined to the yarn axis, so the resolved axial contribution falls and strength decreases. This gives the characteristic twist–strength curve.

Question 41Yarn Manufacture and Yarn Properties

A two-fold yarn is produced by plying two 20 tex single yarns. Ignoring ply twist contraction, the resultant linear density is:

  1. 80 tex
  2. 10 tex
  3. 20 tex
  4. 40 tex Correct answer.

Explanation

When yarns are plied, their masses per unit length add, so two 20 tex singles give approximately 40 tex. Ply twist causes slight contraction that raises the actual value a little, but the nominal sum is the correct basis. Halving or doubling again does not follow the additive rule.

Question 42Yarn Manufacture and Yarn Properties

Compared with a single yarn of the same resultant count, a plied and folded yarn is generally:

  1. More irregular in count and weaker in strength
  2. Free from twist and therefore weaker
  3. More regular, stronger and more resistant to abrasion Correct answer.
  4. Less extensible and more prone to snarling

Explanation

Plying averages out the thick and thin places of the component singles, so the folded yarn is more regular. The balanced ply structure also distributes load across components and reduces the tendency to snarl, giving better strength and abrasion resistance.

Question 43Yarn Manufacture and Yarn Properties

A yarn intended for a hosiery fabric must be soft, extensible and low in twist. Which yarn type best meets this requirement?

  1. A rotor-spun yarn with maximum twist multiplier
  2. A two-fold yarn with balanced ply twist
  3. A low-twist single yarn spun from fine, long-staple cotton Correct answer.
  4. A high-twist combed single yarn

Explanation

Hosiery needs comfort and stretch, so a low-twist single yarn from fine, long-staple cotton gives softness and extensibility. High twist makes the yarn hard and reduces stretch, which is undesirable for knitwear. Balanced ply twist and maximum rotor twist are aimed at other end uses.

Question 44Yarn Manufacture and Yarn Properties

Which statement correctly distinguishes carded from combed cotton yarn?

  1. Combed yarn has short fibres removed, giving greater strength, smoothness and regularity Correct answer.
  2. Combed yarn contains more short fibre and is more irregular
  3. Combed yarn is always coarser than carded yarn of the same count
  4. Carded yarn has passed through an extra combing stage after drawing

Explanation

Combing removes short fibres and neps and further parallelises the fibre, so combed yarn is smoother, stronger and more regular and is used for fine, quality fabrics. Carded yarn retains short fibre and is therefore relatively hairier and less regular.

Question 45Yarn Manufacture and Yarn Properties

In ring spinning, the main function of the traveller running on the ring is to:

  1. Insert twist into the yarn by lagging behind the spindle speed Correct answer.
  2. Remove trash and short fibre from the fibre mass
  3. Parallelise the fibres before drafting
  4. Draft the roving down to the required yarn count

Explanation

The spindle drags the yarn round while the traveller, retarded by friction on the ring, rotates more slowly. This speed difference between traveller and spindle inserts the twist. Drafting is done by the roller pairs, and cleaning and parallelisation occur earlier in the process.

Question 46Yarn Manufacture and Yarn Properties

A rotor-spun yarn is compared with a ring-spun yarn of the same count from the same cotton. Which difference is expected?

  1. Rotor yarn is weaker but more even in count than ring yarn Correct answer.
  2. Rotor yarn is stronger and more regular than ring yarn
  3. Rotor yarn has no twist and cannot be woven
  4. Rotor yarn has higher fibre parallelisation than ring yarn

Explanation

Rotor spinning integrates fibre with a wrapper layer and less parallelisation, which lowers tenacity relative to ring yarn. However, the automated piecing and doubling effect in the rotor gives good count evenness, so rotor yarn is typically more regular but weaker.

Question 47Yarn Manufacture and Yarn Properties

In a yarn evenness test, the coefficient of variation of count (CV%) is reported as 18%. This indicates that:

  1. 18% of the yarn is twist-free
  2. The standard deviation of the linear density is 18% of the mean linear density Correct answer.
  3. The yarn has 18% of its fibres below the mean length
  4. The yarn tenacity is 18% of the fibre tenacity

Explanation

CV% expresses the standard deviation as a percentage of the mean, so a value of 18% means the linear density varies with a standard deviation equal to 18% of the mean. It is a measure of irregularity, not of fibre length, twist or tenacity.

Question 48Yarn Manufacture and Yarn Properties

The irregularity of a yarn is often compared with the limiting irregularity. If the actual CV% is close to the limiting value, the yarn:

  1. Must have been produced by rotor spinning
  2. Has a large amount of additional irregularity from faulty drafting
  3. Contains no short fibres at all
  4. Is close to the best evenness possible for that fibre arrangement Correct answer.

Explanation

Limiting irregularity is the theoretical minimum CV% for a random arrangement of the given fibres. When the measured CV% approaches this limit, the yarn has little extra irregularity from machine or drafting faults. A large gap above the limit signals avoidable irregularity.

Question 49Yarn Manufacture and Yarn Properties

A yarn's tenacity is reported as 18 cN/tex. This quantity expresses:

  1. The twist required to reach maximum strength
  2. The mass of 1000 metres of yarn
  3. The breaking extension as a percentage of the original length
  4. The breaking force normalised by the yarn's linear density Correct answer.

Explanation

Tenacity is breaking force divided by linear density, so cN/tex gives a strength value normalised for yarn thickness. This allows fair comparison between yarns of different counts. Breaking extension, mass per unit length and twist are separate properties.

Question 50Yarn Manufacture and Yarn Properties

Increasing the test gauge length in a yarn strength test generally causes the measured tenacity to:

  1. Remain exactly the same at every gauge length
  2. Increase because more fibres share the load
  3. Become independent of the yarn's irregularity
  4. Decrease because a longer length has a higher chance of containing a weak point Correct answer.

Explanation

A longer test length has a greater probability of including a weak place, so the weakest-link effect lowers the average breaking strength and tenacity. This is why strength values must always be quoted with the gauge length used.