Dispersant selection in the formulation of polypropylene fiber masterbatches, dispersants need to have good compatibility with resin, good affinity with pigments, cohesion.
① Polyethylene wax. Ultra-thin film pigment dispersion requirements are close to those of chemical fiber, so polyethylene wax selection in polypropylene fiber grade masterbatch formulation can refer to the description of dispersant selection in a section of blown film masterbatch formulation.
②Polypropylene wax. The compatibility of polypropylene wax with polypropylene resin is better in both micro and macro aspects. For polypropylene fibers the suitability of polyethylene wax is somewhat limited, especially for fine denier and BCF filaments where polypropylene wax is often preferable to polyethylene wax.
Since the melting point of polyethylene wax is significantly lower than that of PP or polypropylene wax, the different melting characteristics of these two polymers are difficult to handle. The crystalline structure of the fibers changes during the stretching and heat setting of the polypropylene virgin fibers. This temperature can be clearly found in the subsequent heat treatment temperature (carried out at approximately 130°C), which is exactly in the melting temperature range of polyethylene wax.
Due to the change in the crystalline structure of the polypropylene virgin fibers, the molten (and thus liquid) polyethylene wax penetrates from the polypropylene matrix onto the fiber surface, not only as a pure wax, but also as pigments. The polypropylene waxes, if polymerized, are fully compatible with the polymer components, exhibit a very similar melting behavior and melt at approximately the same temperature.
There are two types of polypropylene waxes polymerized by metallocene catalysis: homopolymerized polypropylene waxes with a melting point of 140-160°C and copolymerized polypropylene waxes with a melting point of 80-110°C.
In terms of dispersion theory, in the pigment wetting stage, the low viscosity wax wetting occurs quickly and the wetting efficiency is higher. However, in the later extrusion and pelletizing stage, we want the wax to have a certain viscosity to transfer the shear force between the pigment and the resin melt, so that the wetted pigment can be evenly distributed in the resin melt. At this time we can consider the use of low melting point polypropylene wax in combination with high viscosity polypropylene wax to achieve the best dispersibility.
The lower melting point copolymer polypropylene wax (80~110℃) and higher melting point homopolymer polypropylene baking wax (140~160℃) are selected for compounding. The low melting point copolymer polypropylene wax can quickly melt in the high mixer and start to wet the color powder, and the high melting point homopolymer polypropylene wax provides better shear viscosity during twin-screw extrusion, so the coloring power is increased and the filtering pressure value is decreased compared with the common polyethylene wax (PE520).
③ For carpet fibers, the use of polypropylene wax is definitely not an option. It is different from polyethylene wax, and it will play an unfavorable role in the resilience of the fiber.
④The wax products with too low molecular weight will increase volatility and cause environmental pollution and odor of products, etc.
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