关键词: 尼龙6工业丝, 蠕变机理, 微观结构, WAXD, SAXS

Abstract: Because of their excellent heat resistance, chemical resistance, high strength, and superior elastic properties, nylon 6 industrial fibers are widely used in tire cords, cables, geomaterials, and other industrial fields. Nylon 6 industrial fibers will creep during service under load conditions. The creep process involves changes in their internal microstructure, affecting their service performance. However, the creep properties and structural changes of nylon 6 industrial fibers under different load conditions are still unclear.
In this paper, the creep experiments of nylon 6 industrial fibers across various load ranges (20%‒70% average breaking load, ABL) were conducted, and the difference of creep properties of nylon 6 industrial fibers under different load conditions was compared. The microstructure changes of nylon 6 industrial fibers before and after creep under different load conditions were studied by using wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR), and birefringence techniques.
It can be seen from the creep experiment that the creep deformation rate of the sample increases with the increase of the creep load. When the creep load is not more than 40% ABL, both the elastic recovery rate and creep rate of the sample remain unchanged. However, when the creep load exceeds 40% ABL, there is a decrease in the elastic recovery rate accompanied by an increase in the creep rate. In order to explore the internal structural differences caused by creep at room temperature in nylon 6 industrial fibers under different creep loads, FTIR, WAXD, and SAXS were used to analyze the crystal type transformation, crystallinity, crystallite size, crystal orientation factor, fiber long period and lamellar structure of nylon 6 industrial fibers. Combined with birefringence and dynamic mechanical analysis (DMA), the multilayer structure changes of samples before and after creep tests under different creep loads were studied. The results obtained from FTIR, WAXD, and SAXS indicate that no crystal type transformation occurred during the creep process. Additionally, no significant changes were observed in the crystal structure parameters, including crystallinity, crystallite size, and crystal orientation factor of the nylon 6 industrial fibers. After creep recovery, the changes in the crystal structure of nylon 6 industrial fibers were almost completely recovered. SAXS and birefringence results show that the creep behavior of nylon 6 industrial fibers at room temperature mainly depends on the amorphous structure. When the creep load is low (≤40% ABL), the orientation and thickness of the amorphous zone in the nylon 6 industrial fibers will recover with the removal of the creep load, and when the creep load is high (> 40% ABL), the structure of the crystalline zone and the amorphous zone will recover. The orientation and thickness of the amorphous zone of nylon 6 industrial fibers will increase with the increase of creep load. This is due to the fact that the molecular chains in the amorphous region are oriented along the creep deformation under high creep load, and the molecular chains in the amorphous region with a small degree of orientation are gradually stretched and cannot be completely recovered, and some of the molecular chains in the amorphous region are transformed into oriented amorphous structures, and the thickness of the crystal region increases.

Key words: nylon 6 industrial fibers, creep mechanism, microstructure, WAXD, SAXS