Nylon is the domestic product name of polyamide fiber. There are wide varieties, but their molecular main chains are connected by amide bonds (-C=O-NH-). Foreign names include nylon, nylon, Capron, etc., and is the most developed synthetic fiber in the world. This article mainly understands the performance of nylon.
Compared with polyester, nylon and polyester have many similar properties. The difference is that nylon is not as heat-resistant as polyester, has a lighter specific gravity, has greater moisture absorption than polyester, is easy to dye, and has better strength, wear resistance and fatigue resistance than polyester. , Nylon is more easily deformed, but it has good recovery performance and high resilience. Since the initial modulus is 2-3 times lower than that of polyester, nylon is not as elastic as polyester under the same stress.
The high elongation of nylon brings good resistance to impact and abrasion. The wear resistance of nylon is the best among all fibers, 10 times higher than cotton fiber, 20 times higher than wool,
Among the main synthetic fibers (polyester, nylon, acrylic, vinylon), nylon has the lightest specific gravity – 1.14. Due to its light-specific gravity, nylon is suitable for high-altitude and high-mountain operations. In addition, nylon has high strength, so it can be made into ropes, fishing nets, etc., and can also be spun into spun yarn or made into “hollow fiber”.
When processing nylon, the influence of temperature on fiber properties must be considered. In hot air above 100°C, the strength loss of nylon is obvious, which is due to the oxidative cracking of fiber molecules under the action of heat. When heated without oxygen, the strength loss is very small. In general, the lower the temperature, the higher the strength of nylon. Because the temperature is low, the ability of molecular thermal movement is small, and the intermolecular force is strong. Therefore, the fiber strength is high at low temperatures.
At room temperature, the strength of nylon staple fiber can reach 57.33~66.15cN/tex, and the strength of nylon strong yarn can reach 83.8cN/tex, which is 2~3 times higher than that of cotton fiber. In addition, the increase in temperature will also cause the nylon to shrink, and when it is close to the melting point, the shrinkage will be serious, and the fiber will turn yellow.
The electrical conductivity of nylon is very low, and it is easy to generate static electricity accumulation due to friction during the production process. However, when the relative temperature of the environment increases, the conductivity increases exponentially. For example, when the relative humidity changes from 0 to 100%, the conductivity of nylon 66 increases (10 to the 6th power) times. Therefore, spraying and other wet treatment of nylon fabric during processing can reduce static electricity accumulation.
Hygroscopic Dyeing Properties
Nylon is a hydrophobic fiber, but the macromolecule of nylon contains a large number of weakly hydrophilic groups -C=O-NH-, and there are -NH2 and -COOH hydrophilic groups at both ends of the molecule. Therefore, the hygroscopicity of nylon is higher than that of all synthetic fibers except vinylon. Nylon 6 has a slightly higher hygroscopicity than nylon 66 due to the residual low molecular weight
Nylon will also cause fiber expansion after moisture absorption, but unlike ordinary fibers, the anisotropy of nylon expansion is very small, and the expansion in the longitudinal direction and transverse direction is almost the same. Affected by the stretching of the molecules in the amorphous part, the expansion is larger, resulting in the elongation of the nylon fabric after moisture absorption.
The dyeability of nylon is not as good as that of natural fibers, but it is easy to dye among synthetic fibers. From the molecular structure of nylon, the macromolecule contains a considerable number of -CH- hydrophobic chains, so nylon can be dyed with hydrophobic disperse dyes.
The end of the nylon macromolecule contains amino-NH2 and carboxyl-COOH, and the chain contains imino-NH-.
Nylon macromolecules have dyeing properties similar to wool. In an acidic medium, nylon macromolecules are cationic and can be dyed with anionic dyes; in alkaline media, nylon macromolecules are cationic and can be dyed with cationic dyes, but the soaping and light fastness after dyeing is poor. Therefore less used.
Nylon has better chemical stability, especially alkali resistance. In 10% NaOH solution, treated at 85°C for 10 hours, the fiber strength only decreased by 5%.
The more active group in the nylon macromolecule is the amide group, which will be hydrolyzed under certain conditions.
Acid can hydrolyze nylon macromolecules, causing a decrease in the degree of fiber polymerization, and polyamide macromolecules will also be hydrolyzed in water above 150°C. Acid and heat catalyze fiber hydrolysis.
Strong oxidants can damage nylon, such as bleaching powder, sodium hypochlorite, hydrogen peroxide, etc., and can cause the breakage of the fiber molecular chain and reduce the fiber strength. Moreover, the fabric is easy to turn yellow after bleaching with these oxidants, so if nylon needs to be bleached, sodium chlorite (NaCLO2) or reduced bleach is generally used.