Search for 'superpolymer' led to nylon 75 years ago

The quest for synthetic silk led to the creation of nylon, the versatile engineering resin that's celebrating its 75th birthday this year.

DuPont Co. began commercial production of nylon 6/6 fiber on Dec. 12, 1939, at an $8.5 million plant the firm had built in Seaford, Del., about 90 miles away from the American chemical giant's headquarters in Wilmington.

DuPont's work on developing nylon was led by Wallace Carothers, a legendary researcher who left the faculty of Harvard University to join DuPont in 1928. Carothers was recruited by Charles Stine — another DuPont research legend — and soon began work on several projects at the firm's Experimental Station lab in Wilmington.

While DuPont had made Rayon cellulosic fibers and fabrics since the 1920s, Carothers and other researchers later labored to find new materials by looking at polymers as a “knotted necklace” problem. But where other researchers looked to unravel these materials, DuPont researchers looked to combine them into “superpolymers.” Carothers already had been involved in DuPont's development of Neoprene-brand synthetic rubber, an early materials success for the firm.

“Carothers' idea was to make a superpolymer fiber with a melting point high enough to stand up to normal fabric use, yet low enough to be processed and spun in large quantities,” author Adrian Kinnane wrote in “DuPont: From the Banks of the Brandywine to Miracles of Science,” a company history published in 2003.

In searching for a new material, Carothers had his staff focus on amides — materials made from acids and from ammonia derivatives known as amines. By May 1934, DuPont chemist Don Coffman had made the firm's first superpolyamide. Two months later, chemist Wesley Peterson made a 5/10 polyamide that used castor oil as a feedstock. The material worked, but castor oil couldn't be supplied in large enough quantities to be practical as a raw material.

Then in February 1935, chemist Gerard Berchet made the firm's first 6/6 polyamide fiber. It stood up to dry cleaning solvents, although its high melting point made it hard to process at first. DuPont's ammonia expertise allowed the firm to affordably generate large quantities of HDMA feedstock from adipic acid at its plant in Belle, W. Va. And by working on the spinning process, DuPont improved nylon fiber's maximum spinning time from 10 minutes in 1934 to 82 hours in 1937. Company officials sensed they had a hit on their hands.

Tragically, Carothers would not be there to witness nylon's commercial success. Although a giant in his field, Carothers suffered depression for many years and took his own life on April 29, 1937 — two days after his 41st birthday and a year after he became the first scientist from an industrial research department to be elected to the National Academy of Science.

Carothers' excellence was recognized by his DuPont colleague Elmer Bolton, who said that Carothers “read from the depths of organic chemistry such as I have ever seen.”

Nylon's debut

DuPont pushed on with nylon's commercialization, opening a pilot plant for the fiber in July 1938 at the Experimental Station and setting the stage for Stine's announcing the development of nylon hosiery at the New York World's fair in October of that same year. He described nylon as being “strong as steel, as fine as a spider's web, yet more elastic than any of the common national fibers.” And unlike silk, nylon stockings wouldn't run.

(Read more about the woman behind the nylon leg.)

Almost two years later, that announcement would snowball into nylon's National Sales Day, when 5 million pairs of nylon stockings were sold in a single day. Nylon would go on to earn $3 million of profit for DuPont in those last seven months of 1940 — paying off the project's entire R&D budget.

DuPont had decided not to trademark the term “nylon,” partly as a result of losing a 1938 lawsuit to Sylvania Co. over the term “cellophane.” Names rejected by DuPont before nylon was selected include Delawear, Dusilk, Moorsheen and Silkex.

During World War II, DuPont diverted nylon production to the war effort, where it was used in parachutes, ropes and tents for the U.S military. Stockings were hard to find in war years — a parachute used as much nylon as 2,300 pairs of stockings.

When nylon went back into the stocking market after the war, pent-up demand resulted in lines outside of stores in San Francisco when the products went back on sale in 1946. Demand was even higher because the war had cut off supplies of Japanese silk. In February of that year, Macy's took out an ad in The New York Times apologizing to customers for running out of nylons. The store had sold 50,000 pairs in less than six hours Feb. 5.

The commercialization and production of nylon also benefited from DuPont knowing how to make fibers via its Rayon fiber product line and from the firm's ammonia business being able to make raw materials needed for nylon production.

Other markets

“Nylon was a remarkable product developed at a fortuitous time,” Kinnane wrote. And although nylon's debut was focused around fibers and fabric and stockings — to the point where the term “nylons” essentially became a synonym for “stockings” — the material soon also was used as a molding resin and found an important home in the automotive market.

“Nylon proved to be a fantastic material for automotive use,” Richard Mayo — DuPont's current director of engineering polymers, including nylon — said in a recent phone interview. “It became the go-to resin among engineering resins. For powertrains, under-hood applications — it takes it on the chin and keeps on rolling.”

Mayo is global business director for DuPont Performance Polymers, including its nylon products. He's been with the firm for more than 20 years in a variety of sales, technology and management roles.

Nylon had been used as molding resin as early as 1941 — two years after its debut — in self-lubricating bearings. From the late 1940s to early 1960s, nylon was focused on less critical automotive applications, DuPont scientists Eric Carlson and Ken Nelson wrote in a 2003 article about nylon's automotive past.

These applications included valve stems, wiring clips and windshield wiper systems. One significant early automotive nylon use came in 1956 when French carmaker Citroen used it to make the first plastic radiator fan.

In 1960, the average car used less than half a pound of nylon. By 1995, that number had mushroomed to almost 9 pounds of nylon per vehicle. The nylon per-car total would hit 11 pounds by 2000 and surpass 14 pounds by 2005.

A major breakthrough came in 1968, when DuPont researchers found a way to reinforce the firm's 6/6 resins with glass and minerals. This made it easier for the material to be processed, and opened the door for nylon to be used in radiators, fuel systems and many other under-hood applications.

“Nylon challenged creative engineers and designers to toss convention aside and expand the envelope of nylon properties to new limits,” Carlson and Nelson wrote.

Mayo added that nylon “has the unique capability to handle a mix of high temperatures under hood and chemical resistance through exposure to road salt, hot oil, gas and exhaust.”

The additions of glass and minerals enhanced nylon's performance, he said, with typical glass loadings of 25 to 35 percent, although nylon compounds with loadings as high as 60 percent have been commercialized.

“As nylon has evolved over the years, a lot of work has been done to expand its performance,” Mayo explained. “It can handle higher temperatures than before. We've promoted usages as high as 230° Celsius.”

When nylon entered the auto market, “it really became the first engineering plastic,” said Paul Blanchard, engineering resins director with the IHS Chemical consulting firm in Houston. “It had strength, heat resistance and chemical resistance. Those are the big three characteristics you need for automotive.

“And when you put glass in, it adds a significant amount of heat resistance and also improves strength,” added Blanchard, who joined IHS in 2007 after spending most of a 30-year engineering plastics career with GE Plastics. “That allowed nylon to compete with metal.”

Initially, the addition of glass to nylon was held up by primitive single-screw extruders, Blanchard explained.

“It took a while to design better screw configurations,” he said. “Twin-screw extruders worked better and had different venting.”

Nylon also got an auto-related boost in the 1970s when government regulations began to require pollution control devices on new vehicles. To keep the weight of these devices down, many of them would be made from nylon.

By the 1980s, nylon dominated fuel efficiency and emission control technologies. The material was used in integrated molds and in snap-fit assemblies. Nylon was used in air intake manifolds in Europe in the 1970s, with its use in those parts spreading elsewhere in the 1980s.

Parts integration then provided a good part of nylon's appeal, according to DuPont's Mayo. “Automakers had observed over the years the ability of nylon and plastic in general to integrate components,” he said. “So instead of five or 10 or 15 metal parts — which could be very difficult and expensive to assemble and heavy — they can be replaced by one or two nylon moldings that can be snapped together or screwed together.

“That would bring in nylon in a very cost-effective way,” he said. “Nylon's advancement was about systems cost as much or more than weight reduction. It could bring value — if you were looking for design and versatility — while taking complexity out.”

In the 1990s, the first high-volume commercial air intake manifolds were made in the U.S. by General Motors and DuPont's auto unit. The material also proved useful in supercharged and turbocharged smaller engines in the 1980s and 1990s. Nylon even was used in what Carlson and Nelson described as “air resonators and fuel tanks with Salvador Dali-like shapes.”

Future is strong

And even more automotive innovation might lie ahead for DuPont and other nylon makers.

“The drive toward cost and weight reduction favors nylon,” said Blanchard, who also praised DuPont's Zytel Plus nylon line and similar high-heat resins introduced recently by other producers.

“It's real apparent now that nylon has gone through a rebirth or evolution and it keeps advancing,” he added. “The new technology extends the age of parts in high-heat environments.”

From that first DuPont plant in Seaford, the nylon market has grown to encompass more than 20 billion pounds of combined resin and fiber capacity worldwide. German chemicals giant BASF SE joined the market shortly after DuPont did, and numerous other companies would enter the field. DuPont and BASF remain in the market today, along with U.S.-based producers Invista, Ascend Performance Materials Inc. and Honeywell International Inc.; European producers Royal DSM (the Netherlands), Lanxess AG (Germany), Radici Group (Italy) and Solvay SA (Belgium); and Asian producers Ube Industries Ltd. (Japan), Formosa Group (Taiwan) and Shenma (China).

The market also has expanded beyond nylon 6/6 to include nylon 6 — another widely produced grade — as well as specialty grades such as nylon 12. Globally, about half of nylon resin production is consumed by the automotive market.

(In a sign of the times, DuPont exited the nylon and polyester fibers business — which had become a high-volume, low-margin business — in 2004 when it sold that unit to Koch Industries Inc. for $4.4 billion Koch kept the business going under its well-known Invista trade name.)

Beyond automotive, DuPont's Mayo said that nylon has found a home in many electrical and electronic applications, including laptop computers, smartphones and gaming consoles, where it's often replaced metal. These applications offer lower consumption than the auto market does, he said, but still allow nylon to provide good value.

Nylon also appears to have a bright future, based on the new high-temp materials cited by Mayo and Blanchard, as well as on the recovering global auto market. The number of nylon capacity additions announced in the last year alone also is an encouraging sign.

In that span, DSM has announced plans for a new nylon resin plant at an undisclosed site in North America, and Honeywell confirmed plans to add almost 90 million pounds of resin capacity in Chesterfield, Va.

In Europe, Lanxess opened a plant with almost 200 million pounds of capacity in Antwerp, Belgium, in July, while Evonik Industries AG added 11 million pounds of capacity for specialty nylon 12 in Marl, Germany, in June. Those moves followed the late May announcement that Polish chemicals firm Grupa Azoty planned to open a plant with almost 180 million pounds of annual nylon 6 capacity in Tarnow, Poland, by 2016.

BASF also bolstered its nylon assets in China earlier this year by adding more than 100 million pounds of compounding capacity for nylon and PBT at its plant in Shanghai.

Although DuPont has no nylon expansion projects at present, Mayo said that the firm “is continuously looking” at its investment needs. “It's important for us to be able to supply our customers, and to be responsible and flexible.”

At IHS, Blanchard added that he's “bullish” about the future of nylon.

“Nylon is a workhorse material that functions nicely across a range of products,” he said. It's kept pace through development, and I don't see any danger that it will slide in the future.

“There's a lot of life left in this baby.”