melt-blown material is made by the fiber itself being thermally melted, producing a thicker non-woven fabric than that made by the spunbond method. Fiber randomization and inter-layer interweaving creates a complex channel structure in the melt-blown material.
The filtering mechanism of a mask involves Brownian diffusion, interception, inertial collision, gravitational settling, and electrostatic adsorption. The first four are physical elements, which are natural characteristics of melt-blown non-woven fabric with a filtering capacity of about 35%. This does not meet the requirements of medical masks, so the material needs to be polarized to charge the fibers and use static electricity to capture the aerosol in which the novel coronavirus is located. Polarization treatment and electrostatic adsorption are completed through the Coulomb force of charged fibers to capture the virus droplets (aerosols).
The principle is to make the surface of the filtering material more open, with strong capture ability for microparticles, and an increased charge density for stronger adsorption and polarization effects on particles. Therefore, the filtering layer of melt-blown non-woven fabric must undergo polarization treatment in order to achieve a filtering efficiency of 95% without changing the breathing resistance, in order to effectively prevent the virus.
The melt-blown fabric for masks needs to ensure both effective blocking and comfortable breathability. The inhalation resistance of medical masks is generally no more than 343.2 pascals (Pa), while that of civilian masks is less than 135 pascals (Pa).
Due to the impact of the epidemic, the demand for melt-blown fabric has remained high. However, there are currently many unqualified melt-blown fabrics on the market. To facilitate enterprise understanding, we briefly summarize several major melt-blown fabric testing items:
The particulate matter detector measures the air extracted from the melt-blown fabric, which is equivalent to the inhaled air, and calculates the particle concentration. In simple terms, the concentration ratio of particles in the air after wearing a mask to that outside the melt-blown fabric is the leakage rate of the fabric.
As we all know, filtration efficiency is a key indicator of the quality of melt-blown fabric. This is also one of the important quality standards for melt-blown fabric, so according to relevant standards, the filtration efficiency (dust-blocking rate) of melt-blown fabric, with particles smaller than 5 microns in diameter, must be greater than 95%. This value of 95% is not an average value, but a value, so the average value of actual products is mostly set at 99% or above.
The extent to which wearing a mask affects breathing is determined by breathing resistance. Therefore, the breathing resistance of the melt-blown fabric of the mask determines the breathability and comfort of the mask when worn. The recommended indicators are that the inspiratory resistance should be ≤350 Pa, and the expiratory resistance should be ≤250 Pa.
Naturally, hygiene indicators are another important key indicator for mask melt-blown fabric. Therefore, the required testing items include: initial polluted bacteria, total bacteria colony, coliform bacteria, pathogenic pus bacteria, total fungal colonies, Escherichia coli, Staphylococcus aureus, Candida albicans and residual ethylene oxide content.
Tip: Masks have two sides, a front and a back, with several folds on the surface and a hard strip on the edge. When wearing a mask, the side with the hard strip should be facing up, as the strip can be used to tighten the nose and ensure the mask's sealing. Then the folds of the mask must face downwards, as if facing upwards, the folds are more likely to retain bacteria, viruses, or dust. Make sure to wear the mask correctly and protect yourself!