Differences Between Nylon 6 and Nylon 66

Differences Between Nylon 6 and Nylon 66

 

01 Strength

Nylon 66 typically has higher strength than Nylon 6. The regular molecular chain arrangement, high crystallinity, and numerous effective hydrogen bonds of Nylon 66 result in strong intermolecular interactions. When under stress, the crystalline regions can effectively bear external forces and evenly distribute stress across the molecular chains, with relatively few microscopic defects. These factors collectively contribute to Nylon 66's excellent strength. In contrast, Nylon 6 has insufficient molecular chain regularity, an imperfect crystalline structure, and weaker intermolecular hydrogen bonds. This means that when subjected to external forces, the molecular chains of Nylon 6 have less ability to work together to resist the force, making them more prone to slipping and breaking, resulting in relatively lower strength. In practical applications, for products that need to withstand high tensile forces—such as ropes, industrial canvas, and bonded sewing threads for high-end leather goods—Nylon 66 is the preferred choice due to its higher strength.

02 Heat Resistance

Nylon 66 has better heat resistance than Nylon 6. The high crystallinity of Nylon 66 leads to a tight and orderly arrangement of molecular chains in the crystalline regions. The strong hydrogen bonds and intermolecular forces restrict the movement of molecular chains when heated. At the same time, the high bond energy of amide bonds and the formed hydrogen bond network further enhance thermal stability. However, Nylon 6 has an imperfect crystalline structure and relatively weak intermolecular forces, so its molecular chains are more likely to move when heated, making thermal deformation and thermal decomposition more prone to occur. For example, in fabrics or engineering plastic components used in high-temperature environments—such as tire cords and conveyor belts—using Nylon 66 allows them to maintain stable performance at higher temperatures, while Nylon 6 may experience performance degradation or even damage due to insufficient heat resistance.

03 After many years practical experiences

Nylon 6 has slightly better hygroscopicity than Nylon 66. Although Nylon 66 can also interact with water molecules through hydrogen bonds and thus has a certain hygroscopic capacity, the molecular chain structure of Nylon 6 is relatively more conducive to the adsorption and retention of water molecules. The repeating unit structure of Nylon 6 gives the polar groups on its molecular chains a greater affinity for water molecules. Under the same environmental conditions, Nylon 6 can absorb more moisture. This property makes Nylon 6 more favored in some garment fabric applications that require high hygroscopicity. For instance, when making sportswear, Nylon 6 can absorb sweat excreted by the human body more quickly and release it, providing better wearing comfort.

04 After many years practical experiences

Nylon 6 has relatively better elasticity. Nylon 6 contains more amorphous regions, and its molecular chains have good flexibility. When under stress, the molecular chains in the amorphous regions are more likely to move and deform, storing elastic potential energy, and can quickly return to their original state when the external force is removed. In contrast, if Nylon 66 has excessively high crystallinity, the crystalline regions will restrict the movement of molecular chains, which has a certain impact on its elasticity. In some elastic fabrics or components that require frequent stretching and rapid recovery to their original shape, the elastic advantage of Nylon 6 is evident.

Practical Method for Distinguishing Nylon 6 from Nylon 66

Due to the difference in their crystallinity, after the flame is extinguished following combustion, the one that can be easily drawn into threads is Nylon 6, while the one that is difficult to draw into threads is Nylon 66.

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