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The tensile force (strength) of polypropylene high strength yarn is affected by raw materials, production technology and post-treatment technology. Combined with a number of industry research and technical literature, the core influencing factors can be summarized as follows:

First, raw material factors

Polypropylene melt Index (MFI)

The lower the melting index, the higher the molecular weight, the greater the entanglement of the molecular chain, and the higher the fiber strength. Under the same spinning temperature, drawing multiple and other process conditions, the fiber strength can be significantly increased for every 1 unit reduction of the melting index (such as from 20g/10min to 15g/10min).

For example, using a polypropylene slice with a melt index of 12g/10min, the finished filament strength can reach more than 7.5g/d after optimization.

Additive and blend technology

By adding nucleating agents such as aluminum dicarboxylate, metallocene polypropylene and atactic polypropylene (RPP), the crystallinity and orientation factors can be adjusted to increase strength and reduce elongation at break. For example, adding 1.6% atactic polypropylene to a formula can significantly increase the preorientation factor in the amorphous region and enhance the overall tensile properties of the fiber.

Second, spinning process parameters

Stretch factor and speed

Tensile ratio: The tensile ratio of the primary fiber contributes the most to the strength. Every time the stretching ratio is increased by 1 times (such as from 5 times to 9.5 times), the fiber strength can be increased by 20%-30%. For example, in one process, the drafting multiple is set to 9.5 times, and the fiber strength reaches 7.51g/d.

Drawing speed: In one-step spinning, the drawing speed (i.e., spinning speed) is negatively related to strength. Too high a speed (such as more than 2000m/min) will lead to insufficient crystallization time, an increased risk of molecular chain slip, and a decrease in strength.

Spinning temperature and cooling conditions

The melt temperature is too high (such as more than 280 ° C) will accelerate the molecular chain cleavage, reduce the molecular weight, resulting in a decline in strength. For example, in one case, the spinning temperature increased from 255 ° C to 270 ° C, and the fiber strength decreased from 7.5g/d to 7.0g/d.

The side-blowing temperature should be controlled at 15℃-18℃ to delay the crystallization rate of the primary fiber and avoid the formation of too many monoclinic crystals (α crystal type) that are not conducive to tensile, so as to optimize the subsequent tensile effect.

Third, post-treatment and process optimization

Heat setting and crystallization control

The fiber is thermally shaped by the hot roller (110℃-140℃) and the hot box (190℃), which can stabilize the three-dimensional crystalline structure, reduce the internal stress, and increase the strength by 10%-15%.

By adjusting the crystallization temperature and the ratio of nucleating agent, a uniform hexagonal crystal (β crystal type) can be formed, and the rigidity and tensile properties of the fiber are improved.

Composite fiber technology

The combination of polypropylene with carbon fiber and glass fiber can break through the performance bottleneck of a single material. For example, the strength of a composite fiber can reach more than 8g/d, which is suitable for high-strength scenarios such as aerospace.

The tension of polypropylene high strength yarn is the result of the synergistic effect of material characteristics and process parameters. Enterprises need to maximize fiber strength through raw material selection with low melt index, process design with high draft multiple, precise temperature control and composite technology application. In the future, with the promotion of intelligent production (such as remote monitoring of process parameters) and bio-based polypropylene technology, the strength and stability of polypropylene high-strength yarn is expected to be further improved.

"Hongyang" brand polypropylene high strength yarn products have small color difference, good color fastness, high strength, and are widely used in decorative belts, safety belts, marking lines, etc.The company's main product:  polypropylene high strength yarn , polypropylene filament, polypropylene air change yarn，polyester air change yarn, ribbon.

Taixing Hongyang New Materials Technology Co., Ltd. has consistently adhered to the "excellent quality, customer first, quality service, adhere to the contract," the purpose, with high-quality products, good reputation, selling the country. Wholeheartedly with the domestic business win-win cooperation and common development!