Polypropylene fiber is composed of propylene polymerization, melt spinning, due to no polar group molecules, intermolecular force is small, and because of the molecular chain more smooth, so the glass transition temperature of polypropylene under 0 ℃, the fiber with must adopt isotactic polypropylene polymerization, make each atom of polypropylene macromolecule and groups in three dimensional space as a regular arrangement, can reach 165-170 ℃, melting point due to propylene attraction between the molecules is small, so the molecular weight of polypropylene resin in 200000 or more, the melt viscosity, therefore, when the melt spinning temperature control at above 100 ℃ higher than the melting point, generally is 285 ℃ or higher. The polypropylene molecular chain is pliable with good regularity, and it is easy to crystallize during spinning. The crystallinity of the primary fiber is up to 50%. When spinning, the temperature of the silk chamber is controlled below 30℃, so that the primary fiber can generate unstable pseudo-hexagonal crystals, which are easy to be stretched during post-processing. The preparation of coarse polypropylene fiber can also be used thin film method short-range spinning equipment, the extruder out of the cured film with grooves on the roller to split into fiber. Polypropylene fiber density is 0.91 g/cm', is the chemical fiber in the light of the species, fiber does not absorb moisture, under standard conditions the moisture regain rate is close to 0, dry and wet state performance without significant change, no mold and no moth. Because of the non-hygroscopicity, dyeing is difficult, the spinning dyeing method can be used to solve the problem of dyeing polypropylene, but the chromatography is not complete.
Polypropylene fiber strength and initial modulus are high, close to polyester, wear resistance and elasticity are good, but when the load increases, polypropylene fiber creep elongation is greater than polyester, under high stress modulus and fracture strength is higher than polyester, so polypropylene fiber is a strong and tough fiber.
Polypropylene fiber glass temperature is very low, so the heat setting effect is not stable. The softening point is 140-150℃, and the melting point is 165-173℃. It is melted on one side and burned slowly on the other side in the flame.
The thermal conductivity in the fiber is the lowest, good insulation performance. Polypropylene is a carbon chain polymer, macromolecular chain without weak links, chemical stability is good, in addition to chloric acid, nitric acid and other oxidation acid destruction, the resistance to other acids is good. Alkali resistance, in addition to the strong caustic soda,
The alkali has no effect on the strength of polypropylene. Polypropylene resistant to general organic solvents such as ethanol, ethyl ether, benzene, acetone, gasoline, tetrachloroethylene are not dissolved in hot benzene and gasoline swelling, can dissolve in hot chlorobenzene, tetrahydronaphthalene and dechydronaphthalene.
Polypropylene fiber has good electrical insulation performance, but it is easy to accumulate static electricity in processing, and the spinnability of pure polypropylene fiber is poor.
Polypropylene fiber is easy to age, because the hydrogen atom on the tertiary carbon atom in the polypropylene macromolecular chain is quite active, which is easy to be affected by light, heat and so on and produces active free radical, and causes the free radical chain degradation reaction, which promotes the break of macromolecular chain. When isotactic polypropylene fibers are stored at 50℃ for one year, they lose their value. In order to prevent aging, spinning often add anti-aging agent, in order to slow down the aging process, the better effect of o-hydroxydiphenyl ketone and nickel containing metal organic compounds, adding 1% to 3% graphite to prevent photosensitive aging is the most effective, but not suitable for the production of white fiber.
Polypropylene fiber due to the manufacturing cost is low, the proportion of small and excellent physical and chemical properties and got rapid development, in addition to a large number of used in the manufacture of industrial fabrics, non-woven fabric, also began to dress, especially because of the polypropylene fiber has a core role in absorption, can through the fabric of the capillary water vapor transfer out, itself is no absorption effect, make the skin dry, is of strong manufacturing sportswear, garment and other manual labor permeable fabric, etc.
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