The Invention of Nylon

Overview

The invention of nylon by Wallace Carothers (1896-1937) in 1935 launched the age of artificial fabrics and established basic principles of polymer chemistry that made plastics an ubiquitous part of civilization. Nylon itself has an unparalleled range of advantageous properties, including high strength, flexibility, and scratch resistance. Nylon has been overtaken in popularity by polyester, but it is still widely used in clothing, carpeting, toothbrushes, and furnishings. Artificial fibers, which make up a multi-billion dollar industry, offer the ability to control characteristics in ways that are impossible with natural fibers. In fact, today's polymers have replaced natural materials in many applications, including most textiles in the U.S. They have provided new materials, such as lightweight, shock-resistant body armor, that have characteristics that are impossible to reproduce by natural methods. Nylon and other polymers have also created environmental concerns and disposal problems, leading to widespread efforts at recycling.

Background

In 1931, U.S. access to silk was in jeopardy, due to political and trading tensions with Japan. There was a great interest in finding a substitute, an artificial fiber. Wallace Hume Carothers made the breakthrough in 1934, thanks to a combination of a systematic approach to research and his deep understanding of polymer chemistry.

Carothers's lab at DuPont was an exception within the world of industrial research. It was dedicated to basic science and allowed top scientists to pursue experiments that were driven by their curiosities, rather than by market demands. This was new for DuPont, which had lured the young chemistry professor from Harvard University.

DuPont was a successful company, founded in 1802, that had built its wealth on explosives. In 1902, competition in gunpowder forced the company to look for new sources of revenue, and its research laboratory was founded. This was the beginning of the company's interest in high molecular weight molecules (macromolecules), and its research laboratory began investigating fibers in 1909. By then, DuPont had become a diversified chemical company with expertise in solvents, acids, and stabilizers. That year, a notable example of success in the field of macromolecules was introduced, Bakelite. Named after Leo Baekeland (1863-1944), Bakelite was the first thermosetting plastic. It was hard, resistant to solvents, and worth a fortune to his company.

So it was that Carothers arrived in 1928 to direct research in organic chemistry. Carothers was an expert in polymers, molecules that are made up of long chains of repeating units. It was an arcane field at the time, with few principles and without even a standard way of naming and classifying compounds. Carothers's approach was both fundamental and practical, and, by 1931, his lab had produced a synthetic form of rubber called neoprene. They had also developed an understanding of radical polymerization, using and creating charged organic molecules in chain reactions that led to large molecules. They determined the compositions of condensation polymers, which were created by the splitting off of water as bonds were formed, and established basic principles for driving these reactions.

When the challenge came to create a new fiber, they were ready. There was precedent for their attempt. Louis Chardonnet (1839-1924) had created a hit at the Paris Exposition of 1891 with rayon, so-called because it was so shiny it seemed to be sending out the rays of the Sun. He first made the material in 1889 by extruding dissolved nitrocellulose through tiny holes and letting the solvent dry. Rayon was the first artificial fiber to be widely used, though the fibers were sometimes weak and could be highly inflammable.

Carothers aimed to create the first fully synthetic fiber. When he combined amine, hexamethyldiamine, and adipic acid in 1934, he was able to produce fibers in a test tube. These were the result of a condensation reaction, and it was a pivotal insight by Carothers that changed this laboratory curiosity into the basis for a new industry. Condensation reactions produce water as a byproduct, and Carothers realized that this water was interfering with further reactions, limiting the size of the fibers. By distilling off the water as it was formed, he was able to produce molecules that were long, strong, and elastic. The molecule was called Nylon 66 because each of the two constituent molecules contained six carbon atoms. DuPont patented nylon in 1935 and brought it to market in 1939.

Impact

Nylon was an immediate success. It found dozens of uses, including in toothbrushes, as fishing lines, surgical thread, and especially stockings (which came to be called nylons). It is the physical properties of nylon that make it so attractive. Nylon, a polyamine, has a high strength to weight ratio, it resists changes to its shape, and doesn't scratch easily. It is resistant to moisture and has flow properties that make it perfect for injection molding.

Nylon lends itself to a wider variety of fabrics than any natural fiber. It can be woven into tricot, reversible knot, taffeta, crepe, satin, velvet fleece, brocade, lace, organza, and seersucker. Each weave takes advantage of the natural properties of the nylon in a different way, making it silky or coarse, shiny or dull, sheer or bulky. This means that anything from lingerie and swimwear to sweaters and gloves can be made from nylon. Beside clothing, nylon has found uses in parachutes, ropes, screening, body armor, and cords for automobile tires.

While replicating the qualities of natural fibers, chemists and chemical engineers use what they have learned about polymers to change the properties of fibers, tuning them to specific tasks by, for example, making them more insulating, lighter weight, or fire resistant. This is true for plastics as well as for textiles, and many of the artificial materials that surround us in everyday life owe their origins to the discoveries of Carothers and his colleagues.

The synthetic textile industry is a huge and growing enterprise. In 1900, manufactured fibers accounted for, at most, 1% of the American fiber market. By 1998, manufactured fibers accounted for 70% of the fiber used. The phenomenon is worldwide, with 16 million metric tons (17,636,684 tons) of synthetic fiber produced annually in Asia, and about a third as much each in Europe and North America. Polyester is the king of textiles, with a market size over three times that of nylon and a worldwide annual market value in the tens of billions of dollars. The impact of artificial fibers on national economies is much higher when mark-ups for finished apparel, marketing, and distribution are factored in.

The new materials that began with nylon also changed the culture and the language. Polyester will always be associated with disco and the fashions of the 70s. The word "plastic" suggests more than just synthetic materials; it also refers to anything that's false in culture and society. One reaction to the ubiquity of synthetic materials has been a market for "natural" foods, fabrics, and furnishings. Two recent developments have made synthetics more popular with the public. First, blends have been used to get the look and feel of natural fibers while getting advantages, such as durability and permanent press, of synthetics. Second, finer threads of polyesters (microfibers 100 times thinner than a human hair) have been developed to improve moisture handling and the feel of the fabric. The features of microfiber polyester are so appealing that it is now frequently used for high fashion. At every level of society, synthetic fibers are clothing the world.

An unintended consequence of the success of nylon is the waste it generates. Synthetic polymers, in contrast to natural polymers like wood, cotton, and silk, are not biodegradable. They represent a significant contribution to dumps and landfills and may persist in the environment for hundreds of years. The recognition of the problem has led to two initiatives: First, many municipalities have started recycling programs, which collect and reuse old plastics in new products. Nylon is an especially good target for recycling because of its high melting point. Manufacturers have made a specific commitment to recycle carpeting (for which 2 billion pounds [907,200,000 kg] of nylon are used each year), but as recently as 1996 only 1% of discarded carpet was finding its way into new carpeting. Second, researchers have begun to develop biodegradable polymers that have the beneficial physical characteristics of traditional synthetic polymers while having a route to biological breakdown, usually by microorganisms. This often involves using a biological material, such as chitin, as a starting material, rather than petroleum products. Biodegradable polymers may have the additional benefit of being good choices for medical uses, such as being the basis for dissolving stitches or providing scaffolding for growing replacement organs.

After his discovery of nylon, Carothers's reputation grew among his peers, and he was the first organic chemist elected to the National Academy of Sciences, but he did not live to see the world that he had created. He committed suicide in 1937, before nylon was commercialized. DuPont, on the other hand, benefited enormously from the products. Not only did nylon add to DuPont's wealth, but the laboratory that Carothers had established went on to create non-stick coatings, spandex fiber, Kevlar, and many other polymers of commercial importance.

PETER J. ANDREWS