关键词: 尼龙66工业丝, 热处理张力, 微观结构, 力学性能, 热收缩

Abstract: With the increasing ratio of radial tires in the tire production, high-strength nylon 66 industrial yarns are widely used as the skeleton material for the production of cord fabrics, rubber hoses, conveyor belts and other products due to their excellent properties such as high strength, good heat and fatigue resistance, great dimensional stability, and particularly their strong adhesion to rubber substrates.
At present, there are few reports on the effects of specific processing steps, such as rubber dipping, vulcanization, and heat setting, on the structure and properties of nylon 66 industrial yarns. In order to explore the changes of corresponding relationships between the mechanical properties and microstructure, supramolecular and chemical structures of nylon 66 industrial yarns under short-term heat treatment, this paper simulated different pre-tensioning conditions during impregnation and post-processing of nylon 66 industrial yarns. The structure and properties of nylon 66 industrial yarns were analyzed by SAXS, WAXD and DMA testing methods. The results showed that after heat treatment with a pre-tension ranging from 0.001 cN/dtex to 0.36 cN/dtex for 5 minutes for nylon 66 industrial yarns, there was no significant change in the crystal structure, including grain size, crystal orientation, and crystallinity, as the pre-tension increases during heat treatment. The main effects were on the non-crystalline structure and conformational transitions. Specifically, when the pre-tension was between 0.001 cN/dtex and 0.20 cN/dtex, the transition of the trans-conformation to the gauche-conformation in nylon 66 industrial yarns was inhibited, slowing down the decreasing trend of the orientation degree in the non-crystalline region; when the pre-tension exceeded 0.20 cN/dtex, the rearrangement of molecular chain segments in the non-crystalline region became dominant, leading to an increase in the content of the trans-conformation, an increase in the orientation degree of the non-crystalline region, and an increase in the long period of the lamellar crystals while their diameter decreases.
The experiments show that in the short-time heat treatment of nylon 66 industrial yarns, setting the pre-tension within a reasonable range can help reduce the loss of mechanical properties during the heat treatment process.

Key words: Nylon 66 industrial yarns, heat-treatment tension, microstructure, mechanical property, thermal shrinkage