Tuesday, September 4, 2012

A Great New British Fibre, Tencel: A rattling good yarn from a tree (1994)

This is a piece written for The Independent by John Emsley - a regular writer on cellulosics - who first mentioned Tencel in the "Plant a tree for Chemistry" article for New Scientist in 1987.  He appears to have spoken to David Giachardi, Gordon Campbell, and Pat White.  The last sentence is particularly prescient!

The first artificial fibre, rayon, celebrates its 100th birthday this year. Courtaulds, the chemical company that was built on its success, has launched a new version of this old polymer - and fashion-conscious Japanese are paying pounds 300 for jackets and jeans made from it. The new fibre is Tencel and it was developed by chemists at the company's research labs in Coventry. Courtaulds is now wondering where to build a pounds 90m plant to supply the European market. Britain is a possible location.
According to the Courtaulds director Dr David Giachardi: 'Tencel is the first new fibre to be launched in 30 years. It is very different from the older forms of rayon, and has a luxurious feel, yet can be used to make tough-wearing clothes.' Marks & Spencer has already testmarketed garments made from Tencel
and found demand quickly exceeded supply.

Tencel, like rayon, is made from wood - from the cellulose component of the tree, the part used to make paper. Cellulose is a natural polymer consisting of hundreds of glucose molecules strung together, like beads on a necklace. It is the world's most abundant organic material, and plants make 50 billion tons of cellulose a year from the carbon dioxide of the Earth's atmosphere. They use it as their main structural material because it resists decay by microbes and digestion by animals (it is the fibre part of our diet).

To convert wood cellulose into fibres for textiles it is necessary to solubilise it. This is not easy because the chains of cellulose polymer cling strongly together. The only way to untangle them and pull them out into fine threads is to dissolve them. For rayon, this is done with caustic soda solution and carbon disulphide. When the viscous solution that ensues is forced through tiny nozzles it forms fibres of rayon, or, through a narrow slit, it emerges as cellophane. At the same time the solution is neutralised with acid to make the cellulose insoluble again. The process is efficient but produces a lot of foul-smelling effluent.

Three million tons of rayon are made each year, but this has long been a declining fraction of the world market in artificial fibres. Rayon once reigned supreme and it still has many advantages: it feels gentle to the skin, it hangs well and it dyes well. Rayon is widely used for underclothes, blouses, dresses, jacket linings and, blended with other fibres, in bed linen, upholstery and curtains. But it has its drawbacks: it creases easily, lacks strength when wet - and it loses wars.

In their attempt to create a self-sufficient state, the Nazis invested heavily in rayon, production rising tenfold from 1933 to 1943. German soldiers were kitted out in uniforms made of rayon, and this is sometimes given as the reason why so many fell victim to frostbite on the Russian front. Even so, Nazi scientists made superb rayon and developed a continuous process of manufacture which was taken over by the Allies at the end of the war to become the standard method of production around the world.

The rayon story began at the end of the last century when the world demand for silk was outstripping supply. Black silk crepe was de rigueur for middle-class widows in mourning, a fashion set by Queen Victoria. Black rayon crepe was just as good and this was the route by which Courtaulds introduced the new fibre.

The company was not the first to market an artificial cellulose fibre. A French chemist, Comte de Chardonnet, introduced a nitrocellulose version in 1884. To begin with it sold well, and production of so-called Chardonnet silk soon reached 10,000 tons per year. Unfortunately, it had the upsetting tendency of bursting into flames, and sometimes it even exploded.

A safer cellulose fibre was developed by Charles Cross, Edward Bevan and Clayton Beadle, working at a small shop in South Avenue, Kew, London. They made the first commercially successful rayon and patented it in 1894. They sold their invention to the well-known silk company, Courtaulds, which began manufacturing it in 1905, although it had to overcome the tricky problem of extruding the new fibre through fine nozzles.

For 90 years the chemistry of the process changed little, but about 15 years ago Courtaulds researchers chanced upon the curious discovery that is set to revolutionise the industry. Pat White, research director in charge of developing Tencel, was there from the beginning: 'It all started when we realised that cellulose would dissolve very well when heated in N-methyl morpholine oxide (NMMO). We then have to remove any water present by applying a vacuum. To turn the resulting viscous solution into the new fibre required a new technology of solvent spinning. The fibre is extruded into air and immediately passed into water to wash out the NMMO. We reclaim this and reuse it, so that there is almost no chemical effluent from a Tencel factory. Recycling recovers over 99 per cent of the NMMO each time.'

But it is not the technology, or the environmental benefits, that sell Tencel, but its quality. It not only has a more luxurious feel and fluid drape, but it also has better wet strength, lower shrinkage and is crease-resistant. Courtaulds is keeping it exclusive by pricing it high, but Dr Giachardi believes that people will be willing to pay the extra for it, as its impact in Japan has proved.

Courtaulds has so far invested more than pounds 54m in research and development and built its first Tencel plant at Mobile, Alabama, producing about 20,000 tons of fibre a year, soon to be tripled. The company is now looking to build a plant in Europe. According to Gordon Campbell, Courtaulds' director in charge of fibres: 'Britain is an ideal place for manufacturing, but there are places in Europe offering regional development grants that make them look more attractive, such as parts of Spain and Germany.'

In the next century, Britons will be walking around in the great new British fibre, Tencel. Whether it will also be British-made remains to be seen.


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