Meltblown process requirements for polymer melt performance

Melt blowing process requirements for polymer melt performance. In theory, all thermoplastic polymer chip raw materials can be used in melt blowing process. The commonly used polymer chip raw materials for melt-blown process are polyester, polyamide, polyethylene, polytetrafluoroethylene, polystyrene, polybutylene terephthalate (PBT), ethylene-methyl acrylate copolymer (EMA ), ethylene-vinyl acetate copolymer (EVA), polyurethane, etc. However, polypropylene is the most widely used raw material for meltblown technology. The main raw material parameters that affect the meltblown process include relative molecular weight and its distribution, melt flow index, polymer degradation performance, slice shape, and impurities. 1. The relative molecular weight and its distribution and the index of the melt flow rate The relative molecular weight and distribution of the raw materials are the most important factors affecting the meltblown process and the performance of the meltblown nonwoven fabric. For the meltblown process, it is generally believed that the low relative molecular weight and narrow relative molecular weight distribution of polymer raw materials are beneficial to the uniformity of the meltblown web. The relative molecular weight of the polymer is inversely proportional to its melt flow index (MFI) and directly 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, which is more suitable for the weaker drafting effect of the meltblown process. Generally, polypropylene, polyethylene and their copolymers mainly consider MFI when designing the meltblown process. For other thermoplastic polymers, melt viscosity or intrinsic viscosity is considered to reflect the relative molecular weight of the raw materials. The use of polypropylene materials with lower MFI can produce stronger meltblown nonwovens. The first application is 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 blowing. With the advancement of science and technology, polypropylene with MFTI of 12 was quickly replaced by MHI35, and polypropylene specially used for meltblown technology appeared, with an MFI of up to 1500. The increase of polypropylene MFI can reduce the working temperature of the screw extruder, increase the melt flow rate, and help reduce the formation of excessively degraded polymers, extend the life of the meltblown die, increase the output, reduce energy consumption, and select additives With greater flexibility. The MFI of polypropylene chips commonly used in meltblown technology in the United States reaches 400, 800, 1200, etc. my country has not yet mass-produced and still relies on imports. The higher the MF∏I of the polypropylene chip, the lower the energy consumption during melt blowing. Compared with MFI30, MFI800 reduces energy consumption by about 25%. If high strength of meltblown nonwovens is required, polypropylene chips of MFI30-35 can generally be used, but the production energy consumption is higher. For oil-absorbing materials and warmth-keeping materials, if only the fiber fineness is considered, chips with high MFI can be used, which can increase yield and reduce energy consumption. The more concentrated the molecular weight distribution, the better the relative molecular weight uniformity of the macromolecules, the easier it is to uniformly heat, melt and obtain a uniform web. Therefore, the melt-blown process requires the relative molecular weight distribution of the polymer raw materials to be concentrated as much as possible. 2. Polymer degradation performance Polymer degradation helps correct polymer melt viscosity and relative molecular weight distribution. There are usually three degradation methods: chemical degradation, mechanical shear degradation and thermal degradation. During or before melt blowing, oxygen or peroxy derivatives can be used to achieve chemical degradation. Increased extrusion rate, heat, and melt residence time can achieve mechanical shear degradation and thermal degradation. For polymer melts, uniform degradation is required to avoid inconsistent degradation of polymer melts, resulting in uneven viscosity and discrete relative molecular weight distribution. At the same time, it is also required not to degrade excessively. 3. Containing impurities The diameter of the spinneret holes of the die used in the melt blown process is small. If the polymer raw materials contain a lot of impurities, it is easy to cause the spinneret holes 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 replacement cycle of the nozzle die, reduce energy consumption, and reduce product production costs.