Man-made fibres: regenerated, synthetic and inorganic

1Why this matters

Man-made fibres are in far more than clothes. The woven sacks that carry maize, rice and cement to Rwandan markets, the stretch in a footballer's shorts, the suits of firefighters, the insulation above a ceiling and the frames of racing bicycles are all made from fibres that did not exist a hundred years ago.

Man-made fibres fall into three branches. This lesson describes the main fibres in each branch, their characteristics and uses, and the environmental cost of fibres made from oil.

2How man-made fibres are formed

Most man-made fibres are formed by forcing a thick liquid through a spinneret, a nozzle with many tiny holes, so that each jet hardens into a long filament. Glass and some other inorganic fibres are made by drawing out melted material into fine strands.

31. Regenerated fibres

A natural material, usually cellulose from wood pulp, is dissolved and re-formed into new fibres. Because they are still cellulose, regenerated fibres are absorbent and comfortable, like cotton.

• Viscose (rayon): soft, absorbent, drapes well, but weak when wet.
• Modal: a stronger, softer kind of viscose, used for underwear and T-shirts.
• Lyocell (first sold as Tencel in 1992): made with a solvent that is recovered and reused, and without the toxic chemical used in the older viscose process; strong, soft and absorbent.
• Acetate: shiny and smooth, used for linings and evening wear; melts with a hot iron.

Fabrics sold as "bamboo" are usually viscose made from bamboo pulp, so they are regenerated, not natural.

42. Synthetic fibres

These are built from chemicals, most of them obtained from petroleum. Besides polyester and nylon, the main ones are:

Shared characteristics of synthetics: strong; low absorbency, so they dry quickly but can feel hot and sticky; resist creasing, moths and mould; build up static electricity; and melt when heated, so they must be kept away from a hot iron and from charcoal stoves.

Environmental cost: they are made from oil, which is not renewable; they do not rot, so they stay in the environment for many years; and every wash sheds tiny fibres (microfibres) that travel into rivers and lakes. Some polyester is now made by recycling used plastic bottles, which reuses the plastic instead of throwing it away.

53. Inorganic man-made fibres

• Glass fibre: fine strands of glass. As fluffy glass wool it is a building insulation; set in plastic resin it makes fibreglass for boats and tanks; and very pure glass fibres (optical fibres) carry internet signals as light.
• Carbon fibre: extremely strong, stiff and light, but expensive; used in racing bicycles, aircraft and sports equipment.
• Metallic fibres: fine metal or metal-coated threads that give gold and silver shine to party fabrics and embroidery.

Shared characteristics: they do not burn and do not absorb water; they are very strong but stiff, and glass fibres can break into tiny splinters that irritate skin, eyes and lungs.

Worked example: the right man-made fibre for the job

Worked calculation. A pair of sports leggings weighs 200 g and its label says 82% nylon, 18% elastane. Mass of elastane = 18% of 200 g = 0.18 × 200 = 36 g; mass of nylon = 200 − 36 = 164 g. A small amount of elastane is enough to make the whole garment stretch.

Practice

Solution. Regenerated: lyocell, acetate. Synthetic: acrylic, polypropylene. Inorganic: carbon fibre, glass wool.

Solution. Polypropylene is less dense than water; it is the lightest of the common synthetic fibres.

Solution. 0.20 × 150 = 30 g of elastane (and 120 g of nylon).

Solution. Problems (any two): they are made from oil, which is not renewable; they do not rot; washing sheds microfibres into rivers and lakes. Reduce: buy fewer, longer-lasting clothes; choose recycled polyester; repair and reuse garments.

Solution. Glass fibres break into tiny sharp splinters that irritate the skin, and if breathed in they irritate the throat and lungs.