How a mask protects you?
How a mask protects you? it mostly depend on how good the melt-blowing in the mask is. Melt-blowing (also as melt blown method or melt blow molding) is the conventional manufacturing method of microfibers and nanofibers, and the basis of melt blown non-woven fabric (melt blown cloth for short) production technology. CDC directors also told the media: masks provide more protection than a vaccine on Sep 16, 2020.
This technology extrudes molten polymer (ie polymer melt) through a small nozzle surrounded by high-speed blow molding gas, thereby forming a randomly deposited non-woven sheet product, which is suitable for filtration, adsorption, clothing production and drug delivery system. The substantial benefits of meltblown technology are its simplicity, high specific productivity, and no solvent handling.
Choosing the right combination of polymers with the best rheology and surface properties, scientists have been able to produce meltblown fibers with an average diameter as small as 36 nm
Meltblown non-woven fabrics are mainly used to filter micron particles such as dust, microorganisms, and smog, which can be called the “heart” of masks. It is made up of polypropylene superfine fibers randomly distributed and bonded together, and the appearance is white, flat and soft. The material fiber fineness is 0.3-7.0 microns.
The random distribution of fibers provides more opportunities for thermal bonding between fibers, thus making melt blown The gas filter material has a larger specific surface area and a higher porosity (≥75%). After high-voltage electret electrostatic treatment, it has the characteristics of low resistance, high efficiency and high dust capacity.
The unique dense fine-denier fiber structure of the meltblown non-woven fabric increases the number and surface area of the fiber per unit area, and the gap is extremely fine. This physical structure has a filtering effect of about 30%. Also through high-voltage electret electrostatic treatment, the fiber negatively has electrostatic adsorption capacity, and the filtering effect can be increased to more than 80%, so it has good air filtration.
Both small particles and large particles are easily filtered by the meltblown non-woven fabric. Nanometer-level non-oily particles with a diameter of less than 0.1 microns can be electrostatically adsorbed, and the filtering effect is as high as 99%. Particles with a diameter greater than 10 microns can be absorbed by the physical structure of the interwoven yarn. Even the worst gauze mask can achieve a protection rate of close to 80%.
The most difficult thing to filter is particles with a diameter in the 0.3 micron range. Therefore, my country’s testing standards for masks use 0.3 micron sodium chloride particles as the testing indicators. Meltblown non-woven fabrics with a thickness of less than 0.1 mm can filter 0.3 micron sodium chloride particles by more than 70%. The virus exists in droplet and aerosol state droplet nuclei, of which 82% of the droplet nuclei are in the range of 0.74-2.12 microns in diameter.
Therefore, melt-blown non-woven fabrics have become core materials such as masks and HEPA filter papers, which can effectively prevent viruses and play an irreplaceable role in the medical and health fields.
Medical masks generally use SMS (spunbond-meltblown-spunbond) composite multi-layer structure. The S inside and outside is spunbond non-woven fabric, English is Spunbond; the middle M is meltblown non-woven fabric, English is Melt blowing. The outer layer of medical surgical masks and medical N95 masks need to use waterproof non-woven fabrics, which are mainly used to isolate the patient’s droplets and blood; in the middle of medical N95 masks is a thicker meltblown non-woven fabric, which is very Good filterability, the inner layer is ordinary non-woven fabric.
The filter layer of industrial dust masks is mostly melt-blown non-woven fabric or HEPA filter paper made of melt-blown non-woven fabric. The filter cotton and electrostatic cotton of the gas mask also use meltblown non-woven fabric, and the high-end dust filter box uses HEPA filter.