Orlon

The invention: A synthetic fiber made from polyacrylonitrile that
has become widely used in textiles and in the preparation of
high-strength carbon fibers.
The people behind the invention:
Herbert Rein (1899-1955), a German chemist
Ray C. Houtz (1907- ), an American chemist
A Difficult Plastic
“Polymers” are large molecules that are made up of chains of
many smaller molecules, called “monomers.” Materials that are
made of polymers are also called polymers,
and some polymers,
such as proteins, cellulose, and starch, occur in nature. Most polymers,
however, are synthetic materials, which means that they were
created by scientists.
The twenty-year period beginning in 1930 was the age of great
discoveries in polymers by both chemists and engineers. During
this time, many of the synthetic polymers, which are also known as
plastics, were first made and their uses found. Among these polymers
were nylon, polyester, and polyacrylonitrile. The last of these
materials, polyacrylonitrile (PAN), was first synthesized by German
chemists in the late 1920’s. They linked more than one thousand
of the small, organic molecules of acrylonitrile to make a polymer.
The polymer chains of this material had the properties that
were needed to form strong fibers, but there was one problem. Instead
of melting when heated to a high temperature, PAN simply
decomposed. This made it impossible, with the technology that existed
then, to make fibers.
The best method available to industry at that time was the process
of melt spinning, in which fibers were made by forcing molten
polymer through small holes and allowing it to cool. Researchers realized
that, if PAN could be put into a solution, the same apparatus
could be used to spin PAN fibers. Scientists in Germany and the
United States tried to find a solvent or liquid that would dissolve
PAN, but they were unsuccessful until World War II began.
Fibers for War
In 1938, the German chemist Walter Reppe developed a new
class of organic solvents called “amides.” These new liquids were
able to dissolve many materials, including some of the recently discovered
polymers. WhenWorldWar II began in 1940, both the Germans
and the Allies needed to develop new materials for the war effort.
Materials such as rubber and fibers were in short supply. Thus,
there was increased governmental support for chemical and industrial
research on both sides of the war. This support was to result in
two independent solutions to the PAN problem.
In 1942, Herbert Rein, while working for I. G. Farben in Germany,
discovered that PAN fibers could be produced from a solution of
polyacrylonitrile dissolved in the newly synthesized solvent dimethylformamide.
At the same time Ray C. Houtz, who was working for E.
I. Du Pont de Nemours inWilmington, Delaware, found that the related
solvent dimethylacetamide would also form excellent PAN fibers.
His work was patented, and some fibers were produced for use
by the military during the war. In 1950, Du Pont began commercial
production of a form of polyacrylonitrile fibers called Orlon. The
Monsanto Company followed with a fiber called Acrilon in 1952, and
other companies began to make similar products in 1958.
There are two ways to produce PAN fibers. In both methods,
polyacrylonitrile is first dissolved in a suitable solvent. The solution
is next forced through small holes in a device called a “spinneret.”
The solution emerges from the spinneret as thin streams of a thick,
gooey liquid. In the “wet spinning method,” the streams then enter
another liquid (usually water or alcohol), which extracts the solvent
from the solution, leaving behind the pure PAN fiber. After air drying,
the fiber can be treated like any other fiber. The “dry spinning
method” uses no liquid. Instead, the solvent is evaporated from the
emerging streams by means of hot air, and again the PANfiber is left
behind.
In 1944, another discovery was made that is an important part of
the polyacrylonitrile fiber story. W. P. Coxe of Du Pont and L. L.
Winter at Union Carbide Corporation found that, when PAN fibers
are heated under certain conditions, the polymer decomposes and
changes into graphite (one of the elemental forms of carbon) but still
keeps its fiber form. In contrast to most forms of graphite, these fibers
were exceptionally strong. These were the first carbon fibers
ever made. Originally known as “black Orlon,” they were first produced
commercially by the Japanese in 1964, but they were too
weak to find many uses. After new methods of graphitization were
developed jointly by labs in Japan, Great Britain, and the United
States, the strength of the carbon fibers was increased, and the fibers
began to be used in many fields.
Impact
As had been predicted earlier, PAN fibers were found to have
some very useful properties. Their discovery and commercialization
helped pave the way for the acceptance and wide use of polymers.
The fibers derive their properties from the stiff, rodlike structure
of polyacrylonitrile. Known as acrylics, these fibers are more
durable than cotton, and they are the best alternative to wool for
sweaters. Acrylics are resistant to heat and chemicals, can be dyed
easily, resist fading or wrinkling, and are mildew-resistant. Thus, after
their introduction, PAN fibers were very quickly made into
yarns, blankets, draperies, carpets, rugs, sportswear, and various
items of clothing. Often, the fibers contain small amounts of other
polymers that give them additional useful properties.
A significant amount of PAN fiber is used in making carbon fibers.
These lightweight fibers are stronger for their weight than any
known material, and they are used to make high-strength composites
for applications in aerospace, the military, and sports. A “fiber
composite” is a material made from two parts: a fiber, such as carbon
or glass, and something to hold the fibers together, which is
usually a plastic called an “epoxy.” Fiber composites are used in
products that require great strength and light weight. Their applications
can be as ordinary as a tennis racket or fishing pole or as exotic
as an airplane tail or the body of a spacecraft.