Nylon 6-6 is named this because of how its molecules link together. This synthetic fabric was the first man-made silk substitute. Developing Nylon 6-6 was the work of an organic chemist who had specialized in the chemistry of polymer molecules as they occur in nature. Then he was able to figure out a formula to make a similar material in the laboratory.
The chemical formula for Nylon 6-6 has a chain of six carbon molecules linked to a chain of six more carbon molecules. Between each chain is an amide group made up of oxygen, carbon, and nitrogen hydroxide. Nylon 6-6 is named for this double chain of six carbon molecules. It is a polymer chain.
Nylon 6-6 can be produced in the laboratory by combining adipoyl chloride with hexamethyline diamine. However, when Nylon 6-6 is made in a factory a different formula is used. There the process involves combining adipic acid with hexamethyline diamine. The result is a strong fiber that mimics silk. Both have parallel chains of amide molecules connected by hydrogen bonds.
It took several years for Wallace Carothers to figure out how to do this polymerizing process to make Nylon 6-6 into a strong enough fabric to replace silk in woman's stockings. After Carothers learned and described how natural polymers (like silk) form, he was hired to head the the E.I. du Pont de Nemous & Co. research and development laboratory. He was able to create a nylon polymer with weak fibers by 1934 but until he learned how to get all of the water out of the fibers, they were too weak to use. The process was perfected by 1935.
Nylon 6-6 was the first man-made thermoplastic. It is an amazingly strong material. It is lightweight, windproof, stretchy, shiny and it is very difficult to damage. Oils, solvents and alcohols do not hurt nylon. However, nylon can begin to disintegrate if it comes into contact with dilute acids. If it is touched by phenols, alkalis, iodine or other acids, it will dissolve.
Nylon 6-6 is the strongest of all the nylons and it has the highest melting point so it is used for quite a few industrial applications. It comes in rods, tubes, and sheets so it can be used for insulation, sound insulation, and to replace rubber or even some metals. Since it doesn't scratch easily, it makes for attractive packaging even for foods and drugs. Both the FDA and the USDA have approved the use of nylon 6-6.