Abstract:

Objective With the continuous expansion of polyamid 6 industrial fiber in engineering applications, it is very important to know the creep properties and the corresponding creep deformation mechanism of polyamid 6 industrial fiber under different conditions. In order to explore the difference of creep behavior and the corresponding deformation mechanism of polyamid 6 industrial fiber in different temperature ranges, the structure and properties of samples obtained under different creep temperature conditions were compared.MethodSynchrotron radiation wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) were adopted to compare and analyze the morphological and structural changes before and after creep process. To determine the relationship between creep performance parameters and multilayer structure parameters at different creep temperatures, the creep mechanism of polyamid 6 industrial fiber under different conditions was analyzed.

Results Polyamid 6 industrial fiber was simulated for creep at different ambient temperatures under the creep load of 40%ABL (average breaking load). When the creep temperature reached 160 ℃ and above, the sample showed fracture during the creep process. Nylon 6 industrial fiber exhibitd different creep properties at glass transition temperature. The initial creep strain, total creep strain, elastic creep strain and plastic creep strain of polyamid 6 industrial fiber increased with increasing creep temperature. When the creep temperature was below the glass transition temperature, the elastic recovery rate of the sample was basically unchanged and close to 99%. The creep rate wasincreased slowly, and the creep resistance of the sample was good. When the creep temperature was above the glass transition temperature, the elastic recovery rate decreased rapidly. The creep rate increased obviously, and the creep resistance of the sample was poor. Polyamid 6 industrial fiber exhibited different creep mechanism at glass transition temperature. The crystal orientation of polyamid 6 industrial fiber region is basically unchanged after the creep process, while the structure of amorphous region changes with the change of creep temperature. The creep behavior of nylon 6 industrial fiber under the creep temperature of not more than 150 ℃ was found to depend mainly on the amorphous structure. With the increase of creep temperature, the amorphous orientation and the whole orientation of polyamid 6 industrial fiber increased. The glass transition temperature of polyamid 6 industrial fiber was also increased. The molecular chains in the amorphous region were oriented along the creep deformation, and the molecular chains in the amorphous region with a small degree of orientation were gradually stretched and cannot be completely recovered, and the lamellar thickness increases. When the creep temperature exceeded the glass temperature, the kinetic capacity of the molecular chains in the amorphous region was enhanced.

Conclusion The creep deformation of the samples increases with the increase of the creep temperature. The elastic recovery rate and creep rate after removing the creep load are basically unchanged when the temperature is below 100 ℃, and the creep temperature is significantly decreased and increased when the creep temperature is exceeded 100 ℃ (higher than the glass transition temperature). The stable crystal structure can recover completely after the creep load is removed. After the creep process, the orientation of the amorphous region, the thickness of the lamellar and the glass transition temperature of the sample increased slightly. Some of the molecular chains of the amorphous region with low orientation degree were further deformed under the creep load and formed the oriented amorphous region. When the creep temperature is higher than 100 ℃, the motility of the molecular chains in the amorphous region is enhanced, resulting in a more obvious degree of change.

Key words: polyamid 6 industrial fiber, crystalline structure, lamellar structure, creep property, creep mechanism