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.