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There are three factors that affect the strength of polypropylene high-strength yarn: melt index, draw ratio, and stretch speed. Below, peace will give you a good explanation.
1. Influence of melt index
The melt index of the raw material indicates the molecular weight of the raw material to a certain extent, and the amount of fiber increases under the same process conditions. When the molecular entanglement is large, the strength of the drawn fiber increases as the molecular weight increases, and when the molecular weight is low, slippage occurs between the molecular chains, which is manifested in a decrease in fiber strength. In the polypropylene high-strength spinning process, several different melt index raw materials were used.
In the trial spinning process, it was found that under the same process conditions, the melt index of the raw materials was different, and the strength of the finished filaments was different, and showed a certain regularity.
Under the same spinning temperature, the same stretching ratio and the same process parameters, the lower the melt index of the polypropylene chips, the higher the strength of the polypropylene high-strength yarn.
2, the effect of stretching multiple
The stretching process of nascent fibers destroys the original structural form of the nascent fibers and generates a new sequence structure. Under the action of tensile stress and thermal effect, the activity of the macromolecular segments is increased, and various structural units slide the fibers. The axial orientation gathers, rearranges and adds new bonding points, so that more molecular chains of the fiber are in a particularly good stress-bearing state, and the regularity (ie, crystallization) of the three-dimensional structure is generated, and the fiber density increases as the stretching ratio increases. .
As the draw ratio increases, the strength of the fiber increases, and the draw ratio contributes more to the strength of the fiber.
3. The effect of stretching speed
In the spinning water line of the one-step polypropylene high-strength yarn, the stretching speed is approximately equal to the spinning speed. The degree of orientation and crystallinity of the fiber are affected by the stretching speed in addition to the stretching factor. In the stretching process of polypropylene primary fibers, two changes must be made. One is to completely destroy the natural crystallinity, and the other is to rearrange and recrystallize the macromolecules. Due to the long molecular chain of polypropylene, such as high tensile speed, the development of tensile deformation can not keep up with the change of tensile stress, the hysteresis is serious, and the macromolecule does not have enough time for orientation and crystallization, showing the strength of the fiber. decline.
Different stretching speeds, that is, different spinning speeds, have different fiber strengths, and the fiber strength decreases as the stretching speed increases.
In summary, the main factors affecting the strength of polypropylene high-strength yarn are the melt index, draw ratio and stretching speed of the raw materials. Among them, the draw ratio contributes a lot to the strength of the polypropylene high-strength yarn.
Therefore, if the strength of the polypropylene high-strength yarn is increased. A variety of ways can be used. At a certain spinning temperature, when the melt index of the raw material is low, higher strength can be achieved under the condition of lower draw ratio. If the melt index of the raw material is higher, it needs to be compared. A large stretching factor can achieve a certain strength. For the same raw material, the finished product can be brought to the required strength by adjusting the draw ratio, spinning speed, spinning temperature, steel blowing temperature and wind speed. Through the reasonable cooperation of the process parameters, it is possible to produce polypropylene high-strength yarn with high strength and good quality.
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