Polypropylene fiber technology

Polypropylene (PP) is the first synthetic fiber produced by Italy in 1960. It is the first isotactic (or isotactic) polymer obtained by targeted polymerization of propylene over Zieglar-Natta catalysts. , With high density, high crystallinity and high molecular weight, strength is similar to polyamide fiber. Polypropylene fiber has good elasticity, absolute hydrophobicity, and small specific gravity (only 0.91). The disadvantage is poor dyeing and aging resistance. Because propylene is a petroleum cracking gas, with ample sources and low prices, the production of polypropylene fiber has developed rapidly and is a promising variety.

The fibers are polymerized from propylene and melt-spun. Because there are no polar groups on the macromolecules, the intermolecular forces are small, and because the molecular chains are relatively flexible, the glass transition temperature of polypropylene is below 0°C. Polypropylene for fibers must be The use of 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 propylene molecules, the molecular weight of the resin generally required in 20 Millions or even more, the melt viscosity is large, and the melt temperature during spinning is controlled to be higher than the melting point by more than 100°C (usually 285°C or more). 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 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, which promote macromolecular chain breakage. 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.