Synthetic Fibres in the Sailing World
Did you realise that the first artificial fibre, artificial silk, later known as viscose and now called rayon, was created in 1799 - before the Battle of Trafalgar? However, since this fibre is derived from wood cellulose, it doesn’t count as a synthetic.
Synthetic fibres consist of man-made polymers - very long molecules with a repeating pattern. There’s a reason why fibres made of polymers are so strong: things break at discontinuities in their structure at the atomic level. Theoretically, a molecule of a polymer could be as long as the piece of string you make from it, which would make it immensely strong - but in practice we create long molecules and persuade them to line up and cling to one another when we extrude them into yarns. That still produces pretty strong yarns.
The first synthetic polymer fibre was another silk replacement: nylon. It was invented in the USA in 1938, and first used as a replacement for hog bristle in toothbrushes. By 1939, just in time for World War II, it was used to produce a fine fibre which the military used to make parachute fabric, and civilians used to make women’s stockings. Nylon is a polyamide.
Nylon is strong, but since its molecule is zigzagged it can be stretched quite a lot before it breaks. That makes it excellent for towropes and anchor ropes, but not much use for sailcloth or halyards.
The next class of polymer fibres that interests us is the polyolefines - polyethylene, often called polythene, and polypropylene. The biggest use of these fibres is in insulating and wicking fabrics for clothing, but polypropylene, which floats, is often used for mooring ropes.
In 1953 a new polymer caused a revolution in the manufacture of sails and running rigging - a synthetic polyester. (One of the natural polyesters is cutin, which forms the outer, wax-holding skin on many plant leaves). When people refer to ‘polyester’, they usually mean polyethylene teraphthalate (PET) which appears under a multitude of brand names. The best known are ICI Terylene® and Dupont Dacron®. This fibre is much stronger than cotton or hemp, and stretches far less. Terylene/Dacron sails were significantly more powerful than cotton ones, could be stored wet without rotting, and retained their shape for longer. The ropes were tough and rot-proof. Soon they appeared in the braided form that we know so well - soft, non-kinking, and with a fluffy outer covering that made them much easier to handle than hemp or cotton - and in a pre-stretched form for halyards.
1961 marked the arrival of aramids (a name derived from aromatic polyamides), a class of polymer that first found use in body armour and as an asbestos substitute. Nomex®, Kevlar®, Twaron® and New Star® are the best-known aramid fibre brand names, and all share the following rather unusual properties:
- highly resistant to abrasion and to organic solvents
- withstand heat - don’t melt, but start to break up at 500°C
- sensitive to UV radiation
Aramid fibres are used because of their strength and very low stretch. However, you must have seen how the golden Kevlar fabric sails on racing yachts gradually turn dark brown? UV does that, and eventually weakens the fabric.
Ultra high molecular weight polyethylene (UHMWPE), also known as high-modulus polyethylene (HMPE) or high-performance polyethylene (HPPE), is a kind of polyethylene. It has extremely long chains, containing around a million atoms. It’s very slippery, has high impact strength, and resists corrosion by most solvents except oxidising acids. The best-known trade names are Dyneema® and Spectra®. Recent improvements in manufacturing techniques have reduced its susceptibility to ‘creep’ (elongation caused by slippage between molecules under high sustained loads), but standing rigging using this fibre has resulted in the revival of the deadeyes and lanyards used in the days of HMS Victory because turnbuckles can’t take up enough slack.
Polybenzoxazole (PBO) is a polyurethane fibre invented in the 1980s, produced under the brand name Zylon®. It has the highest strength and modulus of elasticity (i.e. unstretchability) of any fibre currently on the market.
