Nylon 6-6, also referred to as nylon 6,6, is a type of nylon

Nylon

Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...

. Nylon comes in many types, the two most common for textile and plastics industries are: nylon 6

Nylon 6

Nylon 6 or polycaprolactam is a polymer developed by Paul Schlack at IG Farben to reproduce the properties of nylon 6,6 without violating the patent on its production. Unlike most other nylons, nylon 6 is not a condensation polymer, but instead is formed by ring-opening polymerization. This makes...

 and nylon 6,6.

Composition

Nylon 6,6 is made of hexamethylenediamine

Hexamethylenediamine

Hexamethylenediamine is the organic compound with the formula H2N6NH2. The molecule is a diamine, consisting of a hexamethylene hydrocarbon chain terminated with amine functional groups. The colorless solid has a strong amine odor, similar to piperidine...

 and adipic acid

Adipic acid

Adipic acid is the organic compound with the formula 42. From the industrial perspective, it is the most important dicarboxylic acid: About 2.5 billion kilograms of this white crystalline powder are produced annually, mainly as a precursor for the production of nylon...

, which give nylon 6,6 a total of 12 carbon atoms, and its name.

Physical properties

1. Nylon 6,6 has a melting point of 265°C, high for a synthetic fiber, though not a match for polyesters or aramids such as Kevlar
   Kevlar
   Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...
   
   . This fact makes it resistant to heat and friction and enables it to withstand heatsetting for twist retention.
2. Its long molecular chain results in more sites for hydrogen bonds, creating chemical “springs”, making it very resilient.
3. It has a dense structure with small, evenly spaced pores. This means that nylon 6,6 is difficult to dye, but once dyed it has superior colorfastness and is less susceptible to fading from sunlight and ozone and to yellowing from nitrous oxide.

Manufacturing of Nylon 6-6

1. Hexamethylene diamine and adipic acid are combined with water in a reactor. This produces nylon salt. The nylon salt is then sent to an evaporator where excess water is removed.
2. The nylon salt goes into a reaction vessel where a continuous polymerization process takes place. This chemical process makes molten nylon 6,6.
3. The molten nylon 6,6 undergoes a spinning process, where the nylon 6,6 is extruded and sent through a spinneret, which is a small metal plate with fine holes. The nylon is then air-cooled to form filaments.
4. Nylon's chemical formula is nHOOC-(CH₂)₄-COOH+n H₂N-(CH₂)₆-NH₂---->[-OC-( CH₂)₄-CO-NH-(CH₂)₆-NH-] n+2nH₂O and the part -CO-NH- will stick together becoming Nylon 6,6.

Applications

1. Carpet
   Carpet
   A carpet is a textile floor covering consisting of an upper layer of "pile" attached to a backing. The pile is generally either made from wool or a manmade fibre such as polypropylene,nylon or polyester and usually consists of twisted tufts which are often heat-treated to maintain their...
   
   fiber
2. Apparel
3. Airbags
4. Tires
5. Zip Ties
6. Ropes
7. Conveyor Belts
8. Hoses

Nylon 6,6's longer molecular chain and denser structure qualifies it as a premium nylon fiber, specified most often by professional architects and designers for use in commercial settings like offices, airports, and other places that get a lot of wear and tear. It is also an excellent choice for residential carpet applications.