polyamide

Polyamide refers to polymers in which the repeating units are linked by amide bonds. The term covers aliphatic polyamides (nylons) and semi-aromatic or aromatic polyamides known as aramids. The backbone typically consists of chains of -NH-CO- groups.

Most nylons are produced by condensation of a diamine with a diacid, releasing water, or by polymerizing a lactam via ring-opening. Common examples include nylon 6, produced from caprolactam, and nylon 6,6, produced from adipic acid and hexamethylenediamine. Other nylons include nylon 11 and nylon 12 derived from different precursors. Aramids, such as Kevlar and Nomex, are built from aromatic rings connected by amide linkages and offer higher temperature resistance and flame retardancy.

Properties of polyamides include high mechanical strength, stiffness, and abrasion resistance, along with good chemical resistance. They are usually semicrystalline, and their properties are strongly influenced by moisture absorption, which can cause dimensional changes and affect electrical properties. Glass transition and melting temperatures vary with structure and crystallinity.

Processing and applications: polyamides can be melt-processed into fibers, films, or molded parts. Nylon fibers are widely used in textiles and industrial applications; polyamide resins serve as engineering plastics for automotive components, electronics, and packaging. Aramids are used for flame-resistant textiles and high-performance composites.

Environmental aspects: polyamides are generally recyclable by mechanical or chemical methods; hydrolytic degradation can occur under high temperatures and humidity, influencing end-of-life considerations.