Elmer Keiser Bolton - Synthetic Fibers

Synthetic Fibers

When Wallace Carothers arrived at DuPont in 1928 one of the tasks his group took on was the development of synthetic fibers for textiles. At that time a number of natural polymers such as latex and celluloid were known and some synthetic polymers such as bakelite were also known and relatively common. The General Bakelite Company company was producing about 200,000 tons of Bakelite annually. Unfortunately the existing polymers could not be drawn into fibers and spun into thread, so the opportunity was to manufacture thread from synthetic polymers to replace natural fibers such as cotton.

The approach taken by Carothers' group was to adapt known synthesises that produced short chain polymers to produce long chain molecules. The first break was finding that bifunctional esterification could produce long molecule chains which today are known as aliphatic polyesters, but at that time were called superpolymers. Then there was the key observation by Julian W. Hill in April, 1930 in which it was seen that the superpolymers could be drawn in the molten state to form thin, transparent fibers that were much stronger that the polymers were in the undrawn state. However, the superpolymers the group was able to synthesize either had too low a boiling point and insufficient chemical resistivity or had too high a melting point to be spun. By late 1932 the entire project was discontinued.

Bolton, now the Chemistry department director, refused to give up. Most likely he was aware of the re-discovery of polyethylene by Eric Fawcett and Reginald Gibson at Imperial Chemical Industries in 1933. In early 1934 Bolton urged Carothers to continue the research, and Carothers decided to take another look at polyamides.

Carothers surmised that the problem with the polyamides that had been made from ε-aminocaproic acid was due to cyclization reactions, so he replaced ε-aminocaproic acid with 9-aminononoic acid which would not cyclize. This produced results that were encouraging, so Carother's group prepared polyamides from a variety of compounds including amino acids, dibase acids and diamines. The leading candidate for development became 5/10 polyamide made from pentamethylenediamine and sebic acid. It had the right melting point, the desired properties in fiber form and could be spun without gel formation.

Bolton at this point made a bold and characteristically visionary decision. He decided that practical synthetic fibers could not be made from castor oil, the only practical source of sebacic acid. To use an agricultural product as a primary feedstock would mean the new synthetic material would have very similar mass production problems as existing natural fibers had. Instead he wanted to use benzene as the feedstock for making both adipic acid and hexamethylenediamine to make a 6/6 polyamide.

This polymer was first made early in 1935, and thanks to concurrent development of polyamine spinning technologies, could be spun into fibers. The fibers had high strength and elasticity, were insensitive to common solvents and melted at 263 °C, well above ironing temperatures.

Bolton insisted that every aspect of the synthesis of this polymer be thoroughly worked out in a pilot plant at the Experimental Station. He insisted that the development begin with pure materials then be adapted to use materials available to a plant in bulk.

On October 27, 1938 DuPont announced it would build a plant at Seaford, Delaware to make nylon, the world's first fully synthetic fiber. The Seaford plant was essentially a scaled up version of the pilot plant, and had remarkably trouble-free startup.