Nylon properties

1. General properties of nylon ① Density of nylon: With the increase of methylene content and the decrease of amide content in nylon, the crystallinity and density of nylon decrease. ② Crystallinity of nylon: There are crystalline and non-crystalline regions in the semi-crystalline engineering plastics of nylon. The crystallinity has a great influence on the thermal properties of nylon.Processing conditions have a certain impact on the crystallization of nylon. When injection moulding, the mould temperature is high, the melt cooling time is long, and the crystallinity of the product is high. Nylon with high crystallinity has higher tensile strength, impact strength and thermal deformation temperature. ③ The molecular weight of nylon has a great influence on its mechanical properties. The molecular weight of engineering plastics should be more than 20,000. ④ Air permeability of nylon: Air permeability is an important characteristic of nylon. Nylon has the least permeability to oxygen and other gases. Therefore, it has excellent barrier and is an excellent material for food fresh-keeping packaging. A kind of 2. Structure and Mechanical Properties of Nylon The repetitive units in the main chain of nylon molecule contain polar amide groups, which can form molecular identification hydrogen bonds. They have crystallinity and strong intermolecular interaction. Therefore, nylon has higher mechanical properties and modulus. With the increase of methylene content in nylon main chain, the mechanical strength and modulus decrease, and the impact strength increases. Other ways to improve mechanical strength; the molecular structure is symmetrical, introducing ring and aromatic compounds into the main chain repetitive units.The amide group in the main chain of nylon molecule is a hydrophilic group with water absorption. The smaller the density of amide group, the smaller the water absorption. The mechanical properties of nylon will decrease with the water absorption of nylon.Water absorption of nylon will destroy the hydrogen bond of molecular parts, weaken the interaction force between molecules and play a plasticizing role, resulting in the decrease of strength and modulus of nylon, the increase of impact strength and the great change of product size.