The development of nylon
In the early 1930's, Stine was promoted to DuPont's management committee and Elmer K. Bolton succeeded him as chemical research
director. Bolton's top research priority was the creation of a new synthetic fiber. Thus began the interplay of science and commerce
that marks the development process - the "D" of R&D.
New technology was needed to make the raw materials and to form them into a fiber. The market had to be decided upon, an important
choice for a material that could compete with cotton, silk, wool, and rayon. The decision to focus on hosiery was crucial. It was a
limited, premium market. "When you want to develop a new fiber for fabrics you need thousands of pounds," said Crawford Greenewalt,
a research supervisor during nylon development who later became company president and CEO. "All we needed to make was a few grams
at a time, enough to knit one stocking." In addition, the technology had to be scaled up and a plant built that required materials
of construction that were new at the time. And the time was the Great Depression, not the most propitious moment to take a $27
million gamble -- the cost of nylon from research through the start-up of the new plant at Seaford, Delaware.
Encouraged by Bolton, in 1934 Carothers began a renewed effort to make a polymer suitable for fibers. He chose an ester of a
nine-carbon amino acid as the starting material and produced a polyamide with a high melting point, the first nylon. Carothers'
group then looked at 81 polyamide compositions, including on February 28, 1935, the 66 polymer -- so called because each of the
reacting chemicals, hexamethylene diamine and adipic acid, has six carbon atoms. Polymer 66 was selected for development in part
because both of the raw materials could be made from benzene, readily available from coal.
The initial development took place in the laboratory with equipment that could produce 100 pounds of nylon a week. The operation
was so temperamental that the technicians actually tip-toed in the spinning room. They cautioned visitors to give the operation
only a sidewise glance, for a head-on look would stop the process completely. In 1938, a pilot plant was constructed that could
produce 500 pounds of nylon a day. The pilot plant was critical to getting Seaford up and running in record time.
The technical tasks were many. Consider these examples:
Intermediate chemicals. New manufacturing processes for both adipic acid and hexamethylene diamine were developed
at the Belle, West Virginia, plant, and new equipment was designed to keep the ingredients hot during transport over the
Appalachians to Delaware.
Melt spinning. Before nylon, spinning -- the extrusion of polymer to form filaments (as a spider "spins" its web
or a silkworm a cocoon) -- was done with a solvent. Nylon could be solution-spun, but it also could be spun by melting the polymer.
While this offered advantages, it had never been done. "I had nightmares over melt spinning," said Greenewalt. "The problem was the
melting point of nylon was very close to the decomposition point. We'd get bubbles, because the decomposition products were gases."
The solution, simple in hindsight, was to keep the polymer under high pressure - 4,000 pounds per square inch. Special pumps were
designed to operate at these pressures, with small clearances and with no lubricant other than the polymer itself. A new grade of
stainless steel had to be used that was abrasion resistant.
The high temperatures, 550º F (285º C), posed other problems. Many types of spinning-cell melting grids were designed to find a
candidate that would maintain heated surfaces in spite of the poor thermal conductivity of the polymer. To protect the hot polymer
from oxidation, DuPont used a purified grade of nitrogen, which came to be known as "Seaford-grade nitrogen." In addition, the
spinning assembly involved radically new engineering developments to produce fibers of the required uniformity. Before the plant was
opened, eight different spinning assemblies were constructed, each one embodying the newest ideas.
High-speed spinning and cold drawing. Special equipment was designed for this crucial step. Generators were made to run
the windup of the yarn at a speed of 2,000 feet per minute with virtually no variation. The draw rolls -- between which the yarn was
stretched a uniform amount -- had to be manufactured to a tolerance of 1/100,000th of an inch.
Sizing. The size, or surface coating, itself proved a major problem. The first choice corroded knitting needles and
gummed up the machines. Candidate after candidate was tried and failed. The clock was ticking. DuPont eventually assigned 30 scientists
to work on the problem, and they didn't come up with the answer until the structural steel was up at Seaford and much of the other
equipment was installed.