Published November 1974
Polyamides are long-chain polymers in which the monomer units are linked through -NHCO- groups. The majority of polyamides may be classified according to chemical composition as follows:
- Wholly aromatic
- Aromatic-aliphatic
- Wholly aliphatic
- Alicyclic-aliphatic.
The largest volume polyamides, nylon 6 and nylon 66, are aliphatic polyamides.
In the terminology of the U.S. Federal Trade Commission, "nylons" are fibers made from aliphatic and alicyclic polyamides, and aramids are fibers made from aromatic polyamides having at least 85% of the amide linkages directly attached to two aromatic rings. In everyday use, the terms nylon and aramid refer not only to the fiber but also to the polyamide itself. The high melting point of aramids, an asset in fiber applications, makes their fabrication by molding impractical. Most nylons can be used as plastics in addition to being used as fibers; some, such as nylon 12, are only used as plastics. Some polyamides are used as adhesives and coatings.
As to the outlook for the future growth of the various polyamides, Du Pont's Kevlar®, an aramid, is likely to be produced in large volume within the next few years, because of its increasing acceptance as a tire cord. Du Pont's Nomex® and Monsanto's Durette®, both aramids, are expected to enjoy a fast growth because of their flame retardant properties.
