Fibres and their classification

Fabrics are all around us: bedsheets, towels, school uniforms, bags, curtains, mops, even the tea strainer's cloth. If you pull apart a piece of fabric you get yarns (threads); if you untwist a yarn you get fibres, tiny hair-like units. Fibres are the building blocks: fibres are spun into yarns, and yarns are made into fabrics. Fibres, yarns and fabrics are all called textiles. A finish is then given to improve the fabric's look, feel or performance.

What makes a good textile fibre? For a fibre to be useful it must be plentiful and economical, and above all spinnable. Primary properties for spinning:

• Length: much longer than it is wide, so it can be twisted into yarn.
• Strength (tenacity): strong enough to stand the pulling and tension of spinning and weaving.
• Flexibility: able to bend so it can be twisted and drapes comfortably on the body.
• Cohesiveness (a suitable surface): able to grip other fibres. Cotton's natural twist and wool's tiny scales help the fibres lock together.
• Users also want secondary properties: colour, lustre (natural shine; silk has the most), absorbency (cotton absorbs sweat, so it is comfortable in summer), elasticity (stretching and returning to shape), resilience (springing back after crushing; wool rarely needs ironing), and resistance to abrasion, chemicals, heat and insects.

Staple and filament. Staple fibres are short, measured in centimetres (cotton, wool). Filament fibres are very long, measured in metres or kilometres (silk, and manufactured fibres like polyester). Silk is the only natural filament.

Natural fibres come from plants, animals and minerals:

• Cellulosic (from plants): cotton and kapok (seed hairs); flax (linen), hemp and jute (bast fibres from stems); pineapple and sisal (leaf fibres); coir (from the coconut husk).
• Protein (from animals): wool and other animal hair (goat, camel, rabbit), and silk (the secretion of the silkworm).
• Mineral: asbestos, once used for fireproofing but now rarely used because of health risks.
• Natural rubber is also a natural fibre source.

Manufactured fibres. The first was rayon, known in India as 'art silk', made by chemically treating cellulose from cotton waste or wood pulp. Later fibres were synthesised entirely from chemicals. All manufactured fibres are made in similar steps:

• Prepare a thick spinning solution (or melt).
• Force it through a spinnerette, a nozzle with many tiny holes, like a shower head.
• Harden the emerging streams in air or a chemical bath to form filaments.
• Stretch and often texturise the filaments (give them crimp or bulk).

Kinds of manufactured fibres:

• Regenerated cellulosic: viscose rayon.
• Modified cellulosic: acetate.
• Protein: azlon (from proteins such as milk or soyabean).
• Synthetic: nylon, polyester, acrylic, spandex.
• Mineral: glass and metallic fibres.