In polypropylene fiber spinning applications, the suitability of polyethylene waxes is somewhat limited. For normal fine denier and high quality fibers, especially for soft wool-like, fine denier and BCF filaments suitable for floor coverings and textile outerwear, polypropylene waxes are preferable to polyethylene waxes.
1, Because of the incompatibility of polypropylene and polyethylene, homogeneous mixing in the micro sense is very difficult and this incompatibility leads to phase separation.
2, Because polyethylene waxes have significantly lower melting points than polypropylene or polypropylene waxes, the different melting characteristics of these two polymers are difficult to handle. The inhomogeneity of the product, the unsuitable rheology may lead to breakage of the spinning process and due to these side effects, the physical textile properties of the fiber become worse.
This is where a low viscosity polypropylene wax is needed, due to its low viscosity and good wettability to wet the pigment in a short time. Furthermore, during the stretching and heat setting of polypropylene fibers, it can be noticed from the heat treatment temperature (usually carried out at about 130°C), which is exactly in the range of the polyethylene wax melting temperature.
Due to changes in the crystalline structure of the polypropylene virgin fibers, molten polyethylene wax can be observed to penetrate from the polypropylene matrix to the fiber surface and to bring not only pure wax but also pigments to the surface.
3, The compatibility of the polypropylene wax with the polypropylene resin is good on both micro and macro level and has little influence on the mechanical properties. There are two types of polypropylene waxes that are polymerized using metallocene catalyst technology: homopolymer polypropylene waxes, where the raw material is propylene, and copolymer polypropylene waxes, where the raw material is propylene and ethylene.
Usually, the melting point of homopolymerized polypropylene wax is higher, between 140 and 160°C. The molecular weight can range from several thousand to tens of thousands, and the corresponding Brookfield viscosity also ranges from tens to thousands, with higher crystallinity and higher hardness. The melting point of copolymer polypropylene wax is usually between 80~110℃, the Brookfield viscosity is in the hundreds to thousands or even tens of thousands, and the corresponding molecular weight is in the thousands to tens of thousands. The copolymer polypropylene has a lower crystallinity and therefore a lower melting point due to the addition of ethylene copolymer monomer in the copolymer polypropylene, which disrupts the regular arrangement of propylene molecules.
In the pigment wetting stage, low viscosity wax wetting occurs quickly and the wetting efficiency is higher. However, in the extruded filament requirement. Out of the pelletizing stage, we again want the wax to have a certain viscosity, which can transfer shear force well between the pigment and the resin melt, so that the well-wetted pigment can be evenly distributed in the resin melt. It is possible to consider using a low melting point polypropylene wax in combination with a high viscosity polypropylene wax to achieve the best dispersion.
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