01/08/2011

Topic of the month

Polyamide: flattering and sexy – the nylon story

“Hear Gilberte crossing her legs!” Two friends, Bliss and Corey, next to a tape recorder. “I recorded it when she was wearing nylon stockings. It doesn’t work with silk stockings.” Bliss rewinds the tape and plays the same section over again: “Listen to the way the stockings rub against each other!” Corey listens closely – and so does the audience. Bliss is beside himself even though nothing can be heard by any stretch of the imagination.

A scene from François Truffaut’s 1968 thriller “The Bride Wore Black” (DVD) that manages to amuse and irritate at the same time. The audience is quick to work out what is going on, however: Bliss is being introduced as a quickly aroused playboy – easy prey for the seductive “black widow” who is avenging her murdered bridegroom (Jeanne Moreau in a classic role) and who will later push Bliss off the balcony of his skyscraper flat and see him fall to his death.

The tape recorder scene exposes Bliss as an enthusiastic fan of the erotic: although nothing can be heard, his imaginative powers get the testosterone flowing, because nylon textiles happen to be closely associated with sex appeal, particularly in the Swinging Sixties. And nylon stockings happen to be especially attractive – extremely thin and transparent into the bargain, enclosing the legs like a second skin. A German rhyming couplet puts it in a nutshell: “Eine Frau mutiert zur Nymphe, hüllt sie die Bein’ in Nylonstrümpfe” (“A woman becomes a nymph when she puts on nylon stockings”).

No-one found their predecessors, stockings made from wool and cotton, particularly tantalising, on the other hand. Silk stockings were more provocative, but their high price meant that they could not become a mass product, while they also lost their shape quickly and tended to ladder, i.e. they had to be replaced by a new pair very soon. Although erotic charm was all well and good, women in the late 19th century were more interested in textile fibres that were both hard-wearing and affordable – mainly for practical reasons. The chemical industry realised this: the idea of artificial silk was born.

Everything started with artificial silk
The artificial silk era already began during the fin de siècle – first in France and then in England – with a semi-synthetic fibre that was obtained from cellulose (a component of wood) and made a reputation for itself under the name viscose. Louus Bernigaud de Chardonnet (1839-1924), a pupil of Pasteur, had studied silkworms and had observed that the insects ate cellulose in the form of mulberry leaves and then produced a silk thread from it. In 1891, he succeeded in imitating this process in a laboratory. In the following year, the two Englishmen Charles Frederick Cross (1855-1935) and Edward John Bevan (1856-1921) discovered how to produce a thicker, more supple fibre that they called viscose. In 1910, the English textile company Courtaulds Ltd. set up the first viscose factory in America – the “American Viscose Company” – in Chester/Pennsylvania. The US company DuPont de Nemours, which had its headquarters in Wilmington/Delaware, tried to buy the factory in 1916, but Courtaulds was not interested in selling. A joint venture was therefore established in 1920 between DuPont and “Comptoir des Textiles Artificiels” in Paris, from which DuPont Fibersilk Company emerged. In May 1921, the company produced its first yarn at the factory in Buffalo/New York. Three years later, the viscose fibre was given a new name: “rayon”, made up by combining the English word “ray” with the letters “-on” (from “cotton”). In March 1925, DuPont Fibersilk Company therefore started to operate as DuPont Rayon Company.

Rayon soon became unfashionable with both consumers and textile designers, however – and this was due, of all things, to its sheen. An alternative had to be found, a new artificial fibre with properties that could be exploited more effectively at the commercial level. DuPont had high hopes of the in-house polymer research programme that was headed by Wallace Hume Carothers (1896-1937). In February 1928, the company bosses had tempted Carothers, who had a doctorate in chemistry, away from prestigious Harvard University (Cambridge/Massachusetts), where he had been appointed an instructor in organic chemistry at the age of only 30. Although the introverted Carothers was only too glad to abandon the lecture hall, it took DuPont two attempts to obtain the services of the talented young man. Carothers made his commitment to the company dependent on a guarantee that he would not be under pressure to achieve commercial success in the company’s “Experimental Station”. It is difficult to imagine that this promise was kept, since the aim was to find a substitute for rayon and this substitute was expected to be a huge success. It did, at any rate, take until 1934 before Carothers and his team were able to report that they had developed a polyamide as a completely synthetic chemical fibre, while four more years were to pass before it was ready to go to market.

A short chemistry lesson
Polyamides are amines, organic substances consisting of acids and ammonia derivatives that form long, stable carbon chains via polymerisation. They have high melting points that make processing difficult. Carothers’ aim was therefore to develop a polyamide superfibre that had a melting point which was low enough to allow it to be spun in large quantities while it was also tough enough for textile applications, not least of all dry cleaning. An objective that Donald Coffman, one of Carothers’ assistants, succeeded in achieving first in May 1934. The formulation of the new substance was so expensive, however, that the search for an affordable substitute for rayon had to be continued. At the end of July 1934, Wesley Peterson synthesised a polyamide that was called “polymer 5-10” because of the five carbon atoms in its ammonia and the ten carbon atoms in its acid. Carothers thought he had reached his goal, but the DuPont bosses did not give their approval, because castor oil was one of the ingredients. At the time, the oil obtained from the tropical castor seed was a cheap product that was only used as a laxative which had a foul taste. The DuPont strategists were afraid that using castor oil for polyamide production would increase demand for and thus the market price of castor seeds to such an extent that business with the new artificial fibre was likely to become uneconomic very soon. Since the profits that the company was expecting to generate were high, the production costs had to be kept low, starting with the chemical ingredients. Carothers’ team was therefore sent back to the laboratory. After further months of systematic experimentation, Gérard Berchet, a recruit from the University of Colorado, finally produced the “polymer 6-6” (each of the two original compounds has six carbon atoms) from hexamethyldiamine and adipic acid on 28. February 1935. In Carothers’ opinion, the quality of it was not as high as the “polymer 5-10” and it needed to be worked on, but it found favour – at the latest after ammonia specialists at the DuPont factory in Belle/West Virginia developed a process for obtaining large quantities of the rare hexamethyldiamine from the common adipic acid.

More than 200 technical experts were then consulted, in order to optimise “fibre 66”, as it was named for the time being. First of all, it had to be produced from absolutely pure ingredients and be melted at a precisely controlled temperature, in order to avoid precipitation. This was followed by what is known as the melt spinning process: the hot polyamide melt is filtered and is pumped into a spinning die. The thread that is spun is “stretched” and cools down in seconds during this operation, which gives it tear strength. Then it is wound up consistently, coated with a material that protects it against mechanical stresses during textile production and, finally, dyed. At the time, the engineers faced new problems in each of these production operations – which made them more and more familiar with what they called a fickle fibre. Whereas they could only spin it for ten minutes at a time at the beginning, this figure had already increased to 82 hours by 1937. After the first batch had, finally, been produced internally in the “Experimental Station” and “fibre 66” had been given the new name of “nylon” (see “How nylon got its name”), DuPont spent USD 8.5 million on a special nylon factory in Seaford/Delaware. This factory started operation on 12. December 1939, when the Second World War was starting to led to restrictions on and – finally – the complete interruption of silk deliveries from Japan.

Toothbrushes before stockings
The new superpolyamide was launched on the market in 1938 in a rather unspectacular product: the toothbrush supplied by Dr. West, which replaced the brushes used until then, which were made from wild boar bristles. Advertising focussed primarily on a different consumer product, however, and one that aroused greater interest – the nylon stockings mentioned above. DuPont’s Vice President Charles Milton Stine (1882-1954) took advantage of the advance marketing for the New York World’s Fair to publicise the company’s own product. He announced that the “nylons”, as the transparent stockings were soon known everywhere, were “indestructible” legware, made from threads “as strong as steel, but more elastic than any natural fibre”. The advertising failed to mention the fact that nylon stockings were not immune to laddering (“running”) either – which was, incidentally, the reason why one of the possible brand names originally considered (“Norun”) did not have a chance of being chosen (see “How nylon got its name”). Everyone was already talking about nylon when the World’s Fair was opened on Long Island on 30. April 1939 and it continued to make headlines as one of the highlights of the Fair: models presented nylon stockings from DuPont to the public on a large scale for the first time, while one of these models – “Princess Plastic” – was dressed from head to toe in clothes made from DuPont synthetic fibres. The 10.5-metre-high cast of one of the legs in a nylon stocking caused a sensation too.

DuPont did not forget to investigate demand before the nylon stockings went on sale. Test sales were made, first of all, to the company’s own staff in Seaford, who had never been able to afford silk stockings and now were really keen to buy the more affordable nylons. The stockings were sold publicly for the first time at the Braunstein department store in Wilmington, where the company had its headquarters. Each customer was allowed to buy a maximum of three pairs – and they only got them if they had a local address. Outsiders were therefore forced to stay overnight in Wilmington in order to demonstrate that they had one of the coveted addresses and were thus permitted to buy some of the even more coveted nylons. All the hotels within the city limits were booked out as a result – and the shelves with the entire output of the Experimental Station were sold out within a very short time. The successful dress rehearsal was followed by a phenomenal premiere: DuPont announced that 15. May 1940 would be “Nylon Day” and launched the “stocking made from coal, water and air” (advertising copy) on the market on this day. The initial contingent of five million pairs, which were delivered to New York and Philadelphia, were sold out within hours, in spite of strict limitation to just one pair per customer. This was the start of an unprecedented success story: nylon changed consumption patterns all over the world; women’s stockings became a mass product with which DuPont generated profits of USD 3 million in only 7 months.

The economic success did not stop when nylon was only allowed to be produced for military purposes in 1942, the year that the USA went to war. The polyamide fibre was now used to make such products as parachutes (the amount of nylon needed to make 2,300 pairs of stockings was required for a single parachute), pilot’s uniforms, mosquito nets and hammocks. One war correspondent reported enthusiastically: “Termites ate a hammock made from natural fibres in a single night. The sleeping soldier fell into the dirt on the ground. Termites did not find nylon hammocks at all appetising.” Nylon stockings were also produced, but only in very small quantities – as CIA bribes for European informants ...

After the end of the Second World War, DuPont started civil production of nylon again. In 1950, five of DuPont’s ten production departments were involved in manufacturing artificial fibres or the chemicals required to manufacture them. Further military demand for nylon and rayon during the Korean War (1950-1953) required DuPont’s production capacities too. The company’s total sales exceeded USD 1 billion for the first time in 1949. They already amounted to 1.5 billion in 1953 and reached almost 2 billion in 1957. The company’s share of the global market for artificial textile fibres grew accordingly, from less than one per cent in 1950 to 34 per cent in 1967.

Nowadays, nylon is used to produce not only stockings but also bathing suits (vivana nylon), underwear (crepeset nylon), bags and carpets. The fibre’s versatility is less well-known in the non-textile field: nylon is suitable for use as a tear-resistant material for fishing lines, fishing nets, ship mooring ropes, tennis racket strings and even surgical sewing and implant material. In addition to nylon fibre, there is also nylon resin known as Zytel, which is a standard material for tooling and machines that is as light as it is resistant.

The success story that DuPont has written with nylon has not, however, been quite as focussed or straightforward as this short historical outline might suggest. It was at any rate not clear right from the start where the journey would exactly end – it is a well-known fact that success cannot be planned. Although nylon is not a random by-product, the fact that DuPont had an edge on the competition as a polyamide pioneer is not attributable solely to far-sighted corporate decision-making processes; some good luck was needed too. But let us explain things one at a time:

Up to the end of the First World War, DuPont operated primarily as an explosives manufacturer. Its public image was damaged as a result, the company was criticised as being a war profiteer. The company bosses were keen to shake off the negative image and therefore began to switch production to consumer goods more and more. The aim here was not to abandon the company’s heritage entirely, however; instead of this, the goal was to develop “innocent” new product ideas on the basis of the know-how that had been acquired in the manufacturing of explosives. The objective was to extend the DuPont product family organically by carrying out research into related chemicals; Stine, who has already been mentioned above, held senior responsibility for this as head of the chemical department. A vision that produced practical results: explosives were followed by dyes and, finally, stockings – completely different products at first glance, but ones that are related in key areas at the chemical level. Customers were not, of course, aware of the chemical relationships, so the new nylons – backed by advertising campaigns - were exactly the right medicine to cure the company’s image problem: what could be a stronger contrast to ammunition supplies for soldiers than selling delightfully thin stockings to women?

Development in Germany at the same time
Before – in 1938 – DuPont had been shocked briefly when a delegation from the company travelled to Germany to offer I.G. Farbenindustrie AG a licence for nylon – and was confronted with a development that had been made in Germany at the same time. Paul Schlack (1897-1987), a chemist at the I.G. factory AcetA in Berlin-Lichtenberg, had worked on polyamides independently of Carothers and had also found a superpolyamide in January 1938. Schlack’s development was based on just one raw material, in which both the amine and the acid component were present: e-caprolactam, the “inner” amine of aminocaproic acid. A snow-white powder that looked similar to granulated sugar and that Schlack polymerised by melting it in a thick-walled glass tube, which he then left overnight in an oven at 240°C. The molecular rings opened in this process and formed high-molecular chains. Since aminocaproic acid has 6 carbon atoms, the artificial fibre made from just one component was called “polymer 6”, which is processed by the melt spinning process – like nylon (“polymer 6-6”). The German polyamide had technical properties that were very similar to nylon. The thread was highly elastic and considerably more tear-resistant than natural silk. There was no dispute about the priority of the American invention, however: I.G. received the nylon licence contract in May 1939. “Polymer 6” was initially put solely to military use in Hitler’s Germany. Parachutes were made from it at the I.G. factory in Landsberg an der Warthe during the Second World War. In the post-war period, it then became a synonym for the German economic miracle under the trade name Perlon.

Nylon, neoprene, Nagasaki
The bleakest chapter of the nylon story is probably the fate of the man who invented the material: Wallace Hume Carothers never knew what name his fibre was, finally, given and he did not live to experience its triumphant success. The scientist suffered from chronic depression and committed suicide on 29. April 1937, two days after his 41st birthday, in a hotel room in Philadelphia. The brilliant man, who invented not only nylon for DuPont but also neoprene, i.e. synthetic rubber, had already warned the company about “the regular recurrence of neurotic problems that have an adverse effect on my performance” during his interview for the job. Years before he committed suicide, he showed his staff member Julian Hill a capsule containing potassium cyanide, which he carried around with him attached to a watch chain. Carothers’ morbidly melancholic temperament was obvious to everyone, but no-one thought that he was seriously considering suicide, because his creative powers and personal fame were at their height. On 30. April 1936, almost exactly one year to the day before his suicide, Carothers had been appointed a member of the prestigious National Academy of Sciences; no other scientist who did research for industry had ever been given this honour before. It was not, however, in Carothers’ nature to sit back and enjoy his success, particularly in view of the fact that he was already expecting his powers to wane while they were still at their height: he is supposed to have told a friend that synthetic rubber and artificial silk were enough for one person’s life. It is also reported that he was afraid that he would never have another good idea again. Carothers was spared the Second World War, particularly the atomic bombs that were dropped on Hiroshima and Nagasaki by the US Air Force on 6. and 9. August 1945 – a mission in which his employer was involved: from 1942 onwards, DuPont had participated in the Manhattan Project carried out by the US government in secret laboratories to produce weapons-grade plutonium, which the book about the history of the company that was so successful in making and selling nylon made no secret of, incidentally (Adrian Kinnane, “DuPont: From the Banks of the Brandywine to Miracles of Science”. Bad Homburg: Du Pont de Nemours (Germany)/Westerngrund: Büttner Offsetdruck 2002, 60 pages).

How nylon got its name
Carothers called his superpolyamide “fibre 66”. The company management did not think this name had enough advertising appeal, so a naming committee was appointed that came up with almost 400 different suggestions. “Duparooh”, which was proposed by Ernest Knight Gladding (1888-1958), the head of the rayon department, did not convince a majority of the decision-makers. The acronym was considered to be nothing more than a joke, because it stood for “DuPont Pulls A Rabbit Out Of The Hat”. “Wacara” in honour of Wallace Carothers or “Delawear”, a combination of “wear” and Delaware, the US state in which DuPont produced the polyamide fibre, found too few advocates as well. “Dusilk”, “Rayamide” and “Silkex” were also rejected. Gladding then proposed “Norun”. That sounded good and suggested that the material did not ladder (“no run”), but this name was rejected again because it was not true. Without further ado, “Norun” was changed to “Nuron”, because “nu” sounds like “new”. There was, however, a danger that it would be confused with a nerve tonic (“Neuron”). Gladding replaced the “r” by an “l” and the “u” first by an “i” and than by a “y” – and the word “nylon” was coined. A composition designed to sound good that did not really mean anything, even though claims were subsequently made about meanings on which the word was allegedly based. One of these interpretations is that “nylon” came from “New York” and “London”, because two chemists thought up the word on an intercontinental flight from one of the cities to the other. An alternative which is claimed is that DuPont chose the name “nylon” with the aim of provoking Japanese industry, which would be able to export less silk as a result of the new artificial fibre – this story says that “nylon” stands for “Now You’ve Lost, Old Nippon” ...