How is polypropylene high-strength yarn produced and what is its common production process?
Polypropylene high-strength yarn is usually produced by melt spinning. The polypropylene resin is added to a vertical or horizontal screw extruder to heat and melt, extruded from a spinneret through a metering pump, and cooled in the air to form fibers. The industry also uses the membrane fibrillation method to produce split and membrane-broken fibers.
The characteristics of melt spinning of high-strength polypropylene yarn are: ① Single-head single-pitch screw extruder. In order to adapt to the characteristics of high viscosity and poor fluidity of fiber-forming polypropylene, the screw compression ratio is large, the smaller is 2.8. The segments are as short as possible, and the screw aspect ratio ranges from 20 to 26. ② Due to the large molecular weight, the melt temperature is generally higher than the melting point by ~ 130 ° C during spinning. Methods such as adding a molecular weight regulator can also be used to reduce the spinning temperature. ③ The crystallization speed is faster during the cooling forming process, and the cooling temperature should be slightly lower.
Polypropylene high-strength yarn is now used for short-range spinning or compact spinning, that is, the cooling distance after the melt exits the spinneret is very short, and the hoistway can be less than 1m. For example, the annual production line of 1kt staple fiber, from spinning, stretching, shaping, crimping to cutting, can be placed in a factory with a height of 8m and a length of 30m, with less investment, high efficiency and reduced cost.
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