Nylon

The invention: A resilient, high-strength polymer with applications

ranging from women’s hose to safety nets used in space flights.

The people behind the invention:Wallace Hume Carothers (1896-1937),

an American organic chemist Charles M. A. Stine (1882-1954), an American chemist

and director of chemical research at Du Pont Elmer Keiser Bolton (1886-1968),

an American industrial chemist Pure Research In the twentieth century,

American corporations created industrial research laboratories.

Their directors became the organizers of inventions,

and their scientists served as the sources of creativity.

The research program of

E. I. Du Pont de Nemours and Company

(Du Pont), through its most famous invention—nylon—became the

model for scientifically based industrial research in the chemical

industry.

During World War I (1914-1918), Du Pont tried to diversify,

concerned that after the war it would not be able to expand with

only explosives as a product. Charles M. A. Stine, Du Pont’s director

of chemical research, proposed that Du Pont should move

into fundamental research by hiring first-rate academic scientists

and giving them freedom to work on important problems in

organic chemistry. He convinced company executives that a program

to explore the fundamental science underlying Du Pont’s

technology would ultimately result in discoveries of value to the

company. In 1927, Du Pont gave him a new laboratory for research.

Stine visited universities in search of brilliant, but not-yetestablished,

young scientists. He hired Wallace Hume Carothers.

Stine suggested that Carothers do fundamental research in polymer

chemistry.Before the 1920’s, polymers were a mystery to chemists. Polymeric

materials were the result of ingenious laboratory practice,

and this practice ran far ahead of theory and understanding. German

chemists debated whether polymers were aggregates of smaller

units held together by some unknown special force or genuine molecules

held together by ordinary chemical bonds.

German chemist Hermann Staudinger asserted that they were

large molecules with endlessly repeating units. Carothers shared

this view, and he devised a scheme to prove it by synthesizing very

large molecules by simple reactions in such a way as to leave no

doubt about their structure. Carothers’s synthesis of polymers revealed

that they were ordinary molecules but giant in size.

The Longest Molecule

In April, 1930, Carothers’s research group produced two major

innovations: neoprene synthetic rubber and the first laboratorysynthesized

fiber. Neither result was the goal of their research. Neoprene

was an incidental discovery during a project to study short

polymers of acetylene. During experimentation, an unexpected substance

appeared that polymerized spontaneously. Carothers studied

its chemistry and developed the process into the first successful synthetic

rubber made in the United States.

The other discovery was an unexpected outcome of the group’s

project to synthesize polyesters by the reaction of acids and alcohols.

Their goal was to create a polyester that could react indefinitely

to form a substance with high molecular weight. The scientists

encountered a molecular weight limit of about 5,000 units to the

size of the polyesters, until Carothers realized that the reaction also

produced water, which was decomposing polyesters back into acid

and alcohol. Carothers and his associate Julian Hill devised an apparatus

to remove the water as it formed. The result was a polyester

with a molecular weight of more than 12,000, far higher than any

previous polymer.

Hill, while removing a sample from the apparatus, found that he

could draw it out into filaments that on cooling could be stretched to

form very strong fibers. This procedure, called “cold-drawing,” oriented

the molecules from a random arrangement into a long, linear one of great strength. The polyester fiber, however, was unsuitable

for textiles because of its low melting point.

In June, 1930, Du Pont promoted Stine; his replacement as research

director was Elmer Keiser Bolton. Bolton wanted to control

fundamental research more closely, relating it to projects that would

pay off and not allowing the research group freedom to pursue

purely theoretical questions.

Despite their differences, Carothers and Bolton shared an interest

in fiber research. On May 24, 1934, Bolton’s assistant Donald

Coffman “drew” a strong fiber from a new polyamide. This was the

first nylon fiber, although not the one commercialized by Du Pont.

The nylon fiber was high-melting and tough, and it seemed that a

practical synthetic fiber might be feasible.

By summer of 1934, the fiber project was the heart of the research

group’s activity. The one that had the best fiber properties was nylon

5-10, the number referring to the number of carbon atoms in the

amine and acid chains. Yet the nylon 6-6 prepared on February 28,

1935, became Du Pont’s nylon. Nylon 5-10 had some advantages,

but Bolton realized that its components would be unsuitable for

commercial production, whereas those of nylon 6-6 could be obtained

from chemicals in coal.

A determined Bolton pursued nylon’s practical development,

a process that required nearly four years. Finally, in April, 1937,

Du Pont filed a patent for synthetic fibers, which included a statement

by Carothers that there was no previous work on polyamides;

this was a major breakthrough. After Carothers’s death

on April 29, 1937, the patent was issued posthumously and assigned

to Du Pont. Du Pont made the first public announcement

of nylon on October 27, 1938.

Impact

Nylon was a generic term for polyamides, and several types of

nylon became commercially important in addition to nylon 6-6.

These nylons found widespread use as both a fiber and a moldable

plastic. Since it resisted abrasion and crushing, was nonabsorbent,

was stronger than steel on a weight-for-weight basis, and was almost

nonflammable, it embraced an astonishing range of uses: in laces, screens, surgical sutures, paint, toothbrushes, violin strings,

coatings for electrical wires, lingerie, evening gowns, leotards, athletic

equipment, outdoor furniture, shower curtains, handbags, sails,

luggage, fish nets, carpets, slip covers, bus seats, and even safety

nets on the space shuttle.

The invention of nylon stimulated notable advances in the chemistry

and technology of polymers. Some historians of technology

have even dubbed the postwar period as the “age of plastics,” the

age of synthetic products based on the chemistry of giant molecules

made by ingenious chemists and engineers.

The success of nylon and other synthetics, however, has come at

a cost. Several environmental problems have surfaced, such as those

created by the nondegradable feature of some plastics, and there is

the problem of the increasing utilization of valuable, vanishing resources,

such as petroleum, which contains the essential chemicals

needed to make polymers. The challenge to reuse and recycle these

polymers is being addressed by both scientists and policymakers.