Polyamide fibers are the earliest industrialized synthetic fibers in the world. As a supplier of fiber solutions, Alfa Chemistry offers a wide range of polyamide fiber products, such as polyamide-6 fiber and polyamide-66 fiber.
Sources
Polyamide (PA), commonly known as nylon, is a general term for thermoplastic resins containing repeating amide groups - [NHCO] - on the main chain of the molecule, including aliphatic PA, aliphatic-aromatic PA and aromatic PA. Among them, aliphatic PA has many varieties, large output and wide application.
Common polyamide fibers are mainly derived from two types of polymers. One is polydiacid diamine obtained by polycondensation of diamine and diacid, whose chemical structural formula of long-chain molecule is H-[HN(CH2)xNHCO(CH2)yCO]-OH. A typical example is polyamide-66, the chemical formula of which is shown in the figure below.
The other type is obtained by polycondensation or ring-opening polymerization of lactam, whose chemical structural formula of long-chain molecule is H-[NH(CH2)xCO]-OH. A typical example is polyamide-6, the chemical formula of which is shown in the figure below.
Properties
- Polyamide has good comprehensive properties, including mechanical properties, heat resistance, wear resistance, chemical resistance and self-lubrication, and has a low coefficient of friction, a certain flame retardancy, and easy processing.
- The moisture absorption capacity of polyamide fiber is among synthetic fibers, and the moisture regain can reach about 4.5% under normal atmospheric conditions.
- Polyamide fibers are alkali-resistant and acid-resistant, and their amide groups are easily acid-hydrolyzed, resulting in the cleavage of amide bonds and a decrease in the polymerization degree.
- Polyamide fibers have high strength, strong elongation and good elasticity. The strength of polyamide-6 and polyamide-66 fibers is 4~5.3cN/dtex, and the elongation is 18%~45%. When the elongation is 3% to 6%, the elastic recovery rate is close to 100%.
- The most prominent advantage of polyamide fiber is that its abrasion resistance is higher than that of most other fibers, which is 10 times that of cotton fiber, 20 times that of wool, and 50 times that of viscose fiber.
Structure
Molecular Structure
Polyamides have molecular rigidity and intermolecular hydrogen bonds. Amide groups can form strong hydrogen bonds between chains inside the fiber. Such strong hydrogen bonds can impart unique properties to polyamide fibers, such as high strength at high temperatures, toughness at low temperatures, outstanding elasticity, and high resiliency, etc.
Fiber Structure
Polyamide is a flexible thermoplastic polymer, so it can orient and crystallize inside the fibers at high temperatures. Amorphous and crystalline domains differ in molecular orientation, chain mobility, chain packing, number of hydrogen bonds, and interchain space. This structural difference results in different responses of amorphous and crystalline regions to heat, chemicals, moisture, and loading.
Morphological model for nylon-6 fiber [1]
Applications
In the civilian field, it is generally used to weave socks, scarves, clothing, etc.; in the industrial field, it can be used to manufacture tire cords, ropes, fishing nets, parachutes, etc.
Reference
- M. Najafi, et al. Structure and Properties of High-Performance Fibers, 2017, 199-244.
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