Properties of textile fibres: primary and secondary
Primary properties let a fibre be spun into yarn at all. Secondary properties such as absorbency, elasticity and heat behaviour decide comfort, care and end use.
Primary properties (must-haves for spinning)
- High length-to-width ratio: a fibre must be many times longer than it is wide (textbooks give at least about 100 : 1) so it can be twisted into yarn.
- Tenacity (strength): enough strength to survive spinning, weaving and daily use.
- Flexibility (pliability): it must bend again and again without breaking, so cloth can fold and drape.
- Cohesiveness (spinning quality): fibres must cling together when twisted; cotton's natural twists and wool's scales and crimp help.
- Uniformity: fibres of similar length and fineness give an even yarn.
Secondary properties and why they matter
| Property | Meaning | Effect on use |
|---|---|---|
| Physical shape | Length, fineness, cross-section, surface, crimp | Triangular silk shines; crimp in wool gives bulk and warmth |
| Lustre | Light reflected from the surface | Silk and bright rayon shine; cotton is dull unless mercerised |
| Specific gravity | Weight compared with an equal volume of water | Cotton (about 1.5) feels heavy; nylon (about 1.14) is light |
| Moisture regain and absorbency | Moisture taken up from the air, as a % of dry weight | High regain: comfortable, less static, dyes easily. Low regain: dries fast but feels sticky in heat |
| Elasticity and elongation | Stretch, and return to length after stretching | Nylon and wool recover well; cotton and linen do not |
| Resiliency | Springing back after crushing or folding | Wool and polyester resist wrinkles; cotton and linen crease |
| Thermal behaviour | Effect of heat; flammability | Synthetics are thermoplastic (soften and melt); cotton scorches but takes a hot iron |
| Abrasion resistance | Resistance to rubbing wear | Nylon is best; acetate is poor |
| Chemical reactivity | Effect of acids, alkalis and bleach | Cellulose resists alkali but is harmed by acid; protein fibres the reverse |
| Biological resistance | Resistance to mildew, moths and insects | Mildew attacks damp cotton; moths eat wool; synthetics resist both |
| Electrical conductivity | Ability to lose a static charge | Dry, low-regain synthetics build static and cling |
Main fibres compared
| Fibre | Strength | Moisture regain (approx.) | Wrinkle resistance | Heat and ironing |
|---|---|---|---|---|
| Cotton | Good; stronger wet | 8.5% | Poor | Hot iron; scorches, does not melt |
| Linen | Very good; stronger wet | 12% | Very poor | Hottest iron; does not melt |
| Silk | Very good for its fineness; weaker wet | 11% | Fair | Low to medium iron |
| Wool | Weak; weaker wet | 13-16% (highest) | Excellent | Steam press at medium heat |
| Viscose rayon | Fair; much weaker wet | 13% | Poor | Medium iron; does not melt |
| Nylon | Very high; best abrasion resistance | 4-4.5% | Good | Low iron; melts |
| Polyester | High | 0.4% | Excellent | Low to medium iron; melts |
| Acrylic | Fair | 1.5-2% | Good | Low iron; heat-sensitive, melts |
Working out moisture regain
A cotton sample weighs 10.00 g after oven-drying. After standing in standard air (65% relative humidity) it weighs 10.85 g. Find its moisture regain and its moisture content.
- Water taken up = 10.85 − 10.00 = 0.85 g.
- Moisture regain = water ÷ dry weight × 100 = 0.85 ÷ 10.00 × 100 = 8.5%.
- Moisture content = water ÷ conditioned weight × 100 = 0.85 ÷ 10.85 × 100 = 7.83…, which rounds to 7.8% (one decimal place).
- Regain uses the smaller dry weight as its base, so it is always the larger figure.
Moisture regain 8.5%; moisture content about 7.8%.
Choose high-regain fibres (cotton, linen, khadi) for hot, humid summers, hospital wear and baby clothes, because they absorb sweat. Low-regain polyester dries fast but feels sticky in heat, so a polyester-cotton blend is a common compromise for uniforms.
2 marks: “Define moisture regain.” The weight of moisture a dry fibre takes up from standard air, expressed as a percentage of its oven-dry weight. Wool has the highest; polyester about 0.4%.
5 marks: “Explain the primary properties of textile fibres.” Define primary properties, then explain length-to-width ratio, tenacity, flexibility, cohesiveness and uniformity, each with an example.
10 marks: “Discuss the primary and secondary properties of textile fibres and relate them to end use.” Five primary properties; secondary: shape, lustre, density, regain, elasticity, resiliency, thermal, abrasion, chemical, biological, static; a comparison table; end uses.
Primary properties are L-T-F-C-U: Length ratio, Tenacity, Flexibility, Cohesiveness, Uniformity: 'Long Threads Form Cloth Uniformly'.