24 October 2013

Teflon








The invention: 

Afluorocarbon polymer whose chemical inertness
and physical properties have made it useful for many applications,
from nonstick cookware coatings to suits for astronauts.

The person behind the invention:

Roy J. Plunkett (1910-1994), an American chemist





Nontoxic Refrigerant Sought

As the use of mechanical refrigeration increased in the late 1930’s,
manufacturers recognized the need for a material to replace sulfur
dioxide and ammonia, which, although they were the commonly
used refrigerants of the time, were less than ideal for the purpose.
The material sought had to be nontoxic, odorless, colorless, and not
flammable. Thomas Midgley, Jr., and Albert Henne of General Motors
Corporation’s Frigidaire Division concluded, from studying
published reports listing properties of a wide variety of chemicals,
that hydrocarbon-like materials with hydrogen atoms replaced by
chlorine and fluorine atoms would be appropriate.
Their conclusion led to the formation of a joint effort between the
General Motors Corporation’s Frigidaire Division and E. I. Du Pont
de Nemours to research and develop the chemistry of fluorocarbons.
In this research effort, a number of scientists began making
and studying the large number of individual chemicals in the general
class of compounds being investigated. It fell to Roy J. Plunkett
to do a detailed study of tetrafluoroethylene, a compound consisting
of two carbon atoms, each of which is attached to the other as
well as to two fluorine atoms.

The “Empty” Tank

Tetrafluoroethylene, at normal room temperature and pressure,
is a gas that is supplied to users in small pressurized cylinders. On
the morning of the day of the discovery, Plunkett attached such a
tank to his experimental apparatus and opened the tank’s valve. To
his great surprise, no gas flowed from the tank. Plunkett’s subsequent
actions transformed this event from an experiment gone
wrong into a historically significant discovery. Rather than replacing
the tank with another and going on with the work planned for
the day, Plunkett, who wanted to know what had happened, examined
the “empty” tank. When he weighed the tank, he discovered
that it was not empty; it did contain the chemical that was listed on
the label. Opening the valve and running a wire through the opening
proved that what had happened had not been caused by a malfunctioning
valve. Finally, Plunkett sawed the cylinder in half and
discovered what had happened. The chemical in the tank was no
longer a gas; instead, it was a waxy white powder.
Plunkett immediately recognized the meaning of the presence of
the solid. The six-atom molecules of the tetrafluoroethylene gas had
somehow linked with one another to form much larger molecules.
The gas had polymerized, becoming polytetrafluoroethylene, a solid
with a high molecular weight. Capitalizing on this occurrence,
Plunkett, along with other Du Pont chemists, performed a series of
experiments and soon learned to control the polymerization reaction
so that the product could be produced, its properties could be
studied, and applications for it could be developed.
The properties of the substance were remarkable indeed. It was
unaffected by strong acids and bases, withstood high temperatures
without reacting or melting, and was not dissolved by any solvent
that the scientists tried. In addition to this highly unusual behavior,
the polymer had surface properties that made it very slick. It was so
slippery that other materials placed on its surface slid off in much
the same way that beads of water slide off the surface of a newly
waxed automobile.
Although these properties were remarkable, no applications were
suggested immediately for the new material. The polymer might
have remained a laboratory curiosity if a conversation had not
taken place between Leslie R. Groves, the head of the Manhattan
Project (which engineered the construction of the first atomic bombs),
and a Du Pont chemist who described the polymer to him. The
Manhattan Project research team was hunting for an inert material
to use for gaskets to seal pumps and piping. The gaskets had to be
able to withstand the highly corrosive uranium hexafluoride with
which the team was working. This uranium compound is fundamental
to the process of upgrading uranium for use in explosive devices
and power reactors. Polytetrafluoroethylene proved to be just
the material that they needed, and Du Pont proceeded, throughout
World War II and after, to manufacture gaskets for use in uranium
enrichment plants.
The high level of secrecy of the Manhattan Project in particular
and atomic energy in general delayed the commercial introduction
of the polymer, which was called Teflon, until the late 1950’s. At that
time, the first Teflon-coated cooking utensils were introduced.

Impact

Plunkett’s thoroughness in following up a chance observation
gave the world a material that has found a wide variety of uses, ranging
from home kitchens to outer space. Some applications make use
of Teflon’s slipperiness, othersmake use of its inertness, and others take
advantage of both properties.
The best-known application of Teflon is as a nonstick coating for cookware.
Teflon’s very slippery surface initially was troublesome, when it proved to be
difficult to attach to other materials. Early versions of Teflon-coated cookware
shed their surface coatings easily, even when care was taken to avoid scraping it off.
A suitable bonding process was soon developed, however, and the present coated
surfaces are very rugged and provide a noncontaminating coating that can be cleaned
easily.
Teflon has proved to be a useful material in making devices that
are implanted in the human body. It is easily formed into various
shapes and is one of the few materials that the human body does not
reject. Teflon has been used to make heart valves, pacemakers, bone
and tendon substitutes, artificial corneas, and dentures.
Teflon’s space applications have included its use as the outer skin
of the suits worn by astronauts, as insulating coating on wires and
cables in spacecraft that must resist high-energy cosmic radiation,
and as heat-resistant nose cones and heat shields on spacecraft.





Roy J. Plunkett



Roy J. Plunkett was born in 1910 in New Carlisle, Ohio. In
1932 he received a bachelor’s degree in chemistry from Manchester
College and transferred to Ohio State University for
graduate school, earning a master’s degree in 1933 and a doctorate
in 1936. The same year he went to work for E. I. Du Pont
de Nemours and Company as a research chemist at the Jackson
Laboratory in Deepwater, New Jersey. Less then two years later,
when he was only twenty-seven years old, he found the strange
polymer tetrafluoroethylene, whose trade name became Teflon.
It would turn out to be among Du Pont’s most famous products.
In 1938 Du Pont appointed Plunkett the chemical supervisor
at its largest plant, the Chamber Works in Deepwater, which
produced tetraethyl lead. He held the position until 1952 and
afterward directed the company’s Freon Products Division. He
retired in 1975. In 1985 he was inducted into the Inventor’s Hall
of Fame, and after his death in 1994, Du Pont created the
Plunkett Award, presented to inventors who find new uses for
Teflon and Tefzel, a related fluoropolymer, in

See also :

Buna rubber; Neoprene; Nylon; Plastic; Polystyrene;

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