Polyamidi

Polyamides, or polyamidi in some languages, are a class of polymers defined by repeating amide (-CONH-) linkages in their main chain. They can be aliphatic or aromatic and range from flexible fibers to high‑performance engineering plastics. The presence of amide bonds gives polyamides a combination of strength, stiffness, and chemical resistance, as well as a tendency to absorb moisture from the environment.

Synthesis and structure vary by type. Aliphatic nylons are usually made by condensing a diamine with a diacid (for example nylon 6,6) or by polymerizing a cyclic lactam (as in nylon 6). Aromatic polyamides, or aramids, are produced by polycondensation of aromatic diamines and dicarboxylic acid derivatives. The resulting polymers can be semi-crystalline or highly crystalline, and their properties depend on chain rigidity and hydrogen bonding from the amide groups.

Properties and processing. Polyamides generally exhibit good tensile strength, toughness, and abrasion resistance. They often show excellent chemical resistance but tend to absorb moisture, which can plasticize the material and affect mechanical properties. Thermal properties vary widely: aliphatic nylons typically melt in the 210–270°C range, with glass transitions below 100°C; aramids withstand higher temperatures and retain strength at elevated temps. Processing methods include melt extrusion, injection molding, and fiber spinning (wet or dry).

Applications and considerations. Polyamides are used as fibers in textiles, carpets, and tire cords, and as engineering plastics in automotive, electronics, and consumer goods. Environmental aspects include recyclability and the impact of moisture uptake; some polyamides are recycled mechanically or chemically, while others are more challenging to recycle.