Polypropylene fiber is polymerized from propylene and melted in solution. Because there are no polar groups on the macromolecule, the force between molecules is small, and because the molecular chain is more flexible, the glass transition temperature of polypropylene is below 0 °C, polypropylene for fibers. Must use isotactic polymerization, so that each atom and group of polypropylene macromolecules in the three-dimensional space for a regular arrangement, the melting point of up to 165-170 °C, due to the small attraction between the propylene molecules, so the molecular weight of polypropylene resin In 200,000 or more, the melt viscosity is large, so the melt temperature during spinning is controlled to be higher than the melting point by more than 100°C, and is generally 285°C or even higher. Polypropylene molecular chain is compliant, good in regularity, easy to be crystallized during spinning, the primary fiber crystallinity is as high as 50%, and the filament chamber temperature is controlled below 30° C. during spinning to make the primary fiber unstable pseudo-hexagonal crystal. For ease of post-processing stretching. The preparation of the crude polypropylene fiber can also be performed by a short film spinning apparatus. The cured film from the extruder is split into fibers by a grooved roll.
Polypropylene density is 0.91g/cm', which is the lightest kind of chemical fiber. The fiber does not absorb moisture. Under normal conditions, the moisture regain is close to 0, and there is no obvious change in performance under dry and wet conditions. Because it is not hygroscopic and dyeing is difficult, pre-spin dyeing can be used to solve the problem of polypropylene dyeing, but the chromatogram is not complete.
Polypropylene fiber has higher strength and initial modulus, close to polyester, good abrasion resistance and elasticity, but when the load increases, the creep elongation of polypropylene is greater than that of polyester, and the modulus and breaking strength under high stress are higher than that of polyester. Therefore, polypropylene is a tough fiber.
The glass transition temperature of polypropylene is very low, so the heat setting effect is not stable. The softening point is 140-150°C and the melting point is 165-173°C. It melts on one side of the flame and slowly burns on one side. The thermal conductivity is the lowest in the fiber and the insulation performance is good.
Polypropylene is a carbon chain polymer. The macromolecular chain has no weak links and has good chemical stability. In addition to the destruction of oxidizing acids such as chlorosulfonic acid and concentrated nitric acid, polypropylene has good resistance to other acids. Alkali resistance is strong. In addition to concentrated caustic soda, other alkalis have no effect on polypropylene strength. Polypropylene is resistant to common organic solvents such as ethanol, ether, benzene, acetone, gasoline, and tetrachloroethylene. It is swollen in hot benzene and gasoline, and can be dissolved in hot chlorobenzene, tetralin, and decahydronaphthalene. .
Polypropylene has good electrical insulation properties, but it is prone to accumulate static electricity during processing. Pure polypropylene fibers have poor spinnability.
Polypropylene fibers tend to age because the hydrogen atoms on the tertiary carbon atoms in the polypropylene macromolecular chains are quite lively and susceptible to light, heat, etc. to produce active free radicals, and cause free radical chain degradation reactions that promote macromolecular chain breakage. Some people have experimented with storing isotactic polypropylene fibers at 50°C for one year and the fibers lose their use value. In order to prevent aging, anti-aging agents are often added during spinning to slow down the aging process. The effect is better with o-hydroxybenzophenones and nickel-containing metal organic compounds. Adding 1% to 3% graphite is most effective in preventing photoaging. However, it is not suitable for making white fibers.
Polypropylene fiber has been rapidly developed due to its low manufacturing cost, small specific weight, and excellent physicochemical properties. In addition to being used in a large number of industrial fabrics and non-woven fabrics, polypropylene fiber has also begun to be used for clothing, especially since polypropylene has a wicking effect and can pass. The capillaries in the fabric pass out the water vapor, but they do not absorb any of them and keep the skin dry. They can make sportswear, strong physical labor clothing, and other permeable fabrics.
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