High-efficiency melt-blown cloth takes you to understand the requirements of melt-blown process on polymer melt performance as follows:
In theory, all thermoplastic polymer chip raw materials can be used in the meltblown process. The polymer chip raw materials commonly used in the meltblown process are polyester, polyamide, polyethylene, polytetrafluoroethylene, polystyrene, polybutylene terephthalate (PBT), and ethylene-methyl acrylate copolymer (EMA ), Ethylene-vinyl acetate copolymer (EVA), polyurethane, etc. However, polypropylene is the most widely used raw material for meltblown processes.
The main raw material parameters that affect the meltblown process are relative molecular weight and its distribution, melt flow index, polymer degradation performance, slice shape, and impurities.
1. Relative molecular weight and its distribution and perfusion index
The relative molecular weight of the raw materials and their distribution are the most important factors affecting the performance of meltblown processes and meltblown nonwovens. For the meltblown process, it is generally believed that the low molecular weight and narrow molecular weight distribution of the polymer raw material are beneficial to the uniformity of the meltblown web. The relative molecular weight of a polymer is inversely proportional to its melt flow index (MFI) and proportional to the melt viscosity of the polymer melt. That is, the lower the relative molecular weight of the polymer, the higher the MFI, and the lower the melt viscosity, the more suitable it is for the weaker drafting effect of the meltblown process.
Generally, polypropylene, polyethylene and their copolymers are primarily designed with MFI in mind when designing the meltblown process. When other thermoplastic polymers are meltblown, consider the melt viscosity or intrinsic viscosity to reflect the relative molecular weight of the raw materials.
The use of lower MFI polypropylene raw materials can produce higher strength meltblown nonwovens. The earliest application was ordinary fiber-grade polypropylene raw materials, which have high relative molecular weight and low MFI, usually only 12. The polypropylene must be degraded by means of the high temperature and shear action of the screw extruder during melt blow. With the development of science and technology, polypropylene with MFTI of 12 was soon replaced by MHI35. At the same time, polypropylene for meltblown processes appeared, with an MFI of 1500. The increase of polypropylene MFI can reduce the operating temperature of the screw extruder, increase the melt flow rate, help reduce the formation of excessively degraded polymers, extend the life of the meltblown die, increase yield, reduce energy consumption, and give additives With greater flexibility.
The MFI of polypropylene chips commonly used in the US meltblown process reaches 400, 800, 1200, etc. China has not yet mass-produced them and still depends on imports. The higher the MF∏I of polypropylene chips, the lower the energy consumption during meltblown. Compared with MFI30, MFI800 consumes about 25% less energy.
If the strength of meltblown nonwovens is required, polypropylene chips with MFI 30 to 35 can be generally used, but the energy consumption for production is higher. For oil-absorbing materials and thermal insulation materials, if only the fiber fineness is considered, high MFI chips can be used, which can increase production and reduce energy consumption. The more concentrated the molecular weight distribution, the better the relative molecular weight uniformity of the macromolecules, and the easier it is to uniformly heat, melt, and obtain a uniform web. Therefore, the meltblown process requires the relative molecular weight distribution of the polymer raw materials to be as concentrated as possible.
2. Juling Degradability
Polymer degradation helps to modify polymer melt viscosity and relative molecular weight distribution. There are usually three types of degradation: chemical degradation, mechanical shear degradation, and thermal degradation. Oxygen or peroxy derivatives can be used to achieve chemical degradation during or before melt-blown polymer. Increasing extrusion rate, heat and melt residence time can achieve the purpose of mechanical shear degradation and thermal degradation.
For polymer melts, uniform degradation is required to avoid inconsistent degradation of polymer melts and cause uneven viscosity and discrete relative molecular weight distributions. It is also required not to be degraded excessively.
3． Miscellaneous
The diameter of the spinneret of the die used in the melt-blowing process is small. If the polymer raw material contains a lot of impurities, the spinneret hole is likely to be blocked. Therefore, improving the production environment of polymer chip raw materials, optimizing the chip production process, and reducing the impurity content of the chip can effectively extend the nozzle replacement cycle, reduce energy consumption, and reduce product production costs.