Polyamide, commonly known as Nylon or Polyamide in English, is a general term for thermoplastic resins containing repeating amide groups - [NHCO] - on the molecular main chain, including aliphatic PA, aliphatic aromatic PA, and aromatic PA. Among them, there are many varieties of aliphatic PA, with high yields and wide applications. Its name is determined by the specific number of carbon atoms in the synthesized monomer. Invented by renowned American chemist Carlos and his research team.
molecular structure
The commonly used nylon fibers can be divided into two categories.
One type is polydimethylenediamine, which is obtained by condensation of diamine and diacid. The chemical structure formula of its long-chain molecule is:
H - [HN (CH2) xNHCO (CH2)] - OH
The relative molecular weight of this type of nylon is generally 17000-23000. Different nylon products can be obtained based on the different carbon atom numbers of the used diamines and dicarboxylic acids, and can be distinguished by the number added after the nylon, where the first number is the carbon atom number of the diamine and the last number is the carbon atom number of the dicarboxylic acid. For example, nylon 66 indicates that it is obtained by condensation polymerization of adipic acid and adipic acid; Nylon 610 indicates that it is made from adipic acid and sebacic acid.
The other type is obtained by the condensation or ring opening polymerization of lactam, and the chemical structural formula of its long-chain molecules is:
H - [NH (CH2) xCO] - OH
According to the number of carbon atoms contained in its unit structure, different varieties can be named. For example, nylon 6 indicates that it is obtained through ring opening polymerization of caprolactam containing 6 carbon atoms.
Nylon 6, nylon 66, and other aliphatic nylon are composed of linear macromolecules with amide bonds (- NHCO -). Nylon molecules contain - CO - and - NH - groups, which can form hydrogen bonds between or within molecules, as well as with other molecules. Therefore, nylon has good moisture absorption ability and can form a good crystalline structure.
The - CH2- (methylene) in nylon molecules can only generate weak van der Waals forces, so the molecular chain curl of the - CH2- segment is relatively large. Due to the different number of - CH2- present in various types of nylon, the binding forms of hydrogen bonds between molecules are not completely the same, and the probability of molecular curling is also different. In addition, some nylon molecules also have directionality. The directionality of molecules is different, and the structural properties of fibers are also not completely the same.