First of all, the stretching ratio is an important parameter in the stretching process. Within a certain range, as the stretching ratio increases, the fiber molecular chains gradually align along the stretching direction. For example, when the stretching ratio is low, the molecular chain orientation is loose, and the fiber strength and modulus are limited. However, when the stretching ratio gradually increases, the molecular chains are closely arranged along the direction of stress, and the mechanical properties of the fiber are significantly improved. However, a draw ratio that is too high may cause stress concentration inside the fiber and even breakage. Therefore, the draw ratio needs to be reasonably determined based on the specific use of the fiber and the characteristics of the raw materials.
Secondly, the stretching temperature has a key influence on the fiber orientation structure. Appropriate stretching temperature can enable the polypropylene molecular chains to have appropriate mobility and facilitate rearrangement under the action of stretching force. If the temperature is too low, the molecular chain will be too rigid, making it difficult to achieve effective orientation and prone to stress cracks; if the temperature is too high, the molecular chain will be too active and prone to slipping, resulting in an unstable orientation structure. Generally speaking, for modified polypropylene monofilament fiber, the stretching temperature is usually within a certain range above its glass transition temperature. The specific value needs to be accurately set according to the modification situation and fiber requirements.
Stretch speed cannot be ignored either. A higher stretching speed can quickly orient the molecular chains in a short time, but it will also increase the stress accumulation inside the fiber. In actual production, factors such as equipment performance, fiber quality, and production efficiency must be comprehensively considered to select the appropriate stretching speed. For example, when producing high-strength, high-modulus fibers, the drawing speed can be appropriately increased as long as the equipment allows it, but it needs to be coordinated with subsequent annealing and other processes to eliminate internal stress.
During the stretching process, the crystalline morphology of the fiber also changes. Stretching promotes the regular arrangement of polypropylene molecular chains, which is conducive to the formation and growth of crystals, and the crystals grow oriented along the stretching direction. This crystalline orientation structure further enhances the fiber's strength and stability. By controlling the drawing process parameters, the size, shape and orientation of the crystals can be adjusted to meet the fiber performance requirements of different applications.
Additionally, tension uniformity during drawing is critical to fiber quality. Uneven tension will cause fiber diameter fluctuations and inconsistent orientation structures, thus affecting the overall performance of the fiber. Therefore, an advanced tension control system is needed to ensure that the tension on the fiber is uniform and stable during the entire stretching process.
The drawn fibers can also be further optimized through appropriate post-treatment processes, such as heat treatment, to optimize the orientation structure and eliminate internal stress. Heat treatment can relax the molecular chains to a certain extent, adjust the orientation structure, and improve the dimensional stability and comprehensive performance of the fiber.
By accurately regulating the process parameters such as the stretching ratio, temperature, and speed of modified polypropylene monofilament fiber, and focusing on the tension control and post-processing process during the stretching process, we can effectively achieve precise control of the fiber orientation structure, thereby preparing excellent performance, Modified polypropylene monofilament fiber to meet different application needs.
