Nylon 66

Hexamethylenediamine (top) and adipic acid (bottom), monomers used for polycondensation of Nylon 66.

Nylon -6,6 is synthesized by polycondensation of hexamethylenediamine and adipic acid. Equivalent amounts of hexamethylenediamine and adipic acid are combined with water in a reactor. This is crystallized to make nylon salt, an ammonium/carboxylate mixture. The nylon salt goes into a reaction vessel where polymerization process takes place either in batches or continuously.

$${\displaystyle {\ce {n(HOOC - (CH2)4 - COOH) + n(H2N - (CH2)6 - NH2) -> [-OC - (CH2)4 - CO - NH - (CH2)6 - NH - ]_n + (2n - 1)H2O}}}$$

Removing water drives the reaction toward polymerization through the formation of amide bonds from the acid and amine functions. Thus molten nylon 66 is formed. It can either be extruded and granulated at this point or directly spun into fibers by extrusion through a spinneret (a small metal plate with fine holes) and cooling to form filaments.

In 2011 worldwide production was two million tons. At that time, fibers consumed just over half of production and engineering resins the rest. It is not used in films due to its inability to be oriented. Fiber markets represented 55% of the 2010 demand with engineering thermoplastics being the remainder.[2]

Nylon 66 is frequently used when high mechanical strength, rigidity, good stability under heat and/or chemical resistance are required.[3] It is used in fibers for textiles and carpets and molded parts. For textiles, fibers are sold under various brands, for example Nilit brands or the Cordura brand for luggage, but it is also used in airbags, apparel, and for carpet fibres under the Ultron brand. Nylon 66 lends itself well to make 3D structural objects, mostly by injection molding. It has broad use in automotive applications; these include "under the hood" parts such as radiator end tanks, rocker covers, air intake manifolds, and oil pans,[4] as well as numerous other structural parts such as hinges,[5] and ball bearing cages. Other applications include electro-insulating elements, pipes, profiles, various machine parts, zip ties, conveyor belts, hoses, polymer-framed weapons, and the outer layer of turnout blankets.[6] Nylon 66 is also a popular guitar nut material.[7]

Nylon 66, especially glass fiber reinforced grades, can be effectively fire retarded with halogen-free products. Phosphorus-based flame retardant systems are used in these fire-safe polymers and are based on aluminium diethyl phosphinate and synergists. They are designed to meet UL 94 flammability tests as well as Glow Wire Ignition Tests (GWIT), Glow Wire Flammability Test (GWFI) and Comparative Tracking Index (CTI). Its main applications are in the electrical and electronics (E&E) industry.

The Remington Nylon 66 was a .22 rifle manufactured by Remington Arms from 1959 to 1989. The firearm's stock and receiver were both made from Dupont Zytel, a nylon 6-series polymer.