Face masks and medical protective clothing are made of non-woven fabric. The so-called meltblown, which acts as a filter, gives the products their actual function: a high separation efficiency against the smallest particles, such as bacteria and viruses.
A face mask without meltblown is like a car without an engine"
Meltblown is a nonwoven fabric made of extremely fine, melt-spun microfibres. The fibers are up to seventy times thinner than a human hair and one fiber sometimes has an average thickness of only one micron. The raw materials used for meltblown spunbonds are polymers, e.g. polypropylene is generally used for face masks.
Good filters work like doormen: They only let through what is wanted. This task becomes all the more complex, the smaller the particle size is which needs to be filtered. A simple sieve effect, as known from sandboxes, is no longer effective to handle very small particles, such as viruses and bacteria. In the case of face masks, for example, an additional combination of effects such as inertial impaction, diffusion, and electrostatic attraction are active at the same time.
Sieve effect: Particles larger than a specific size are entrapped in the meshes.
Inertia effect: Larger particles are unable to move in the air flow round the filter fibers. They maintain their direction, hit the fibre and stick there.
Diffusion effect: Very small particles, such as viruses, often move along irregular paths in the air flow. This results in a high possibility probability of contact with filter fibers.
Electrostaticattraction: To enhance diffusion and inertia effect, materials are electrostatically charged in order to filter minute particles. The filter fibers then attract particles like a magnet and entrap them.
There are many different medical face masks. But basically they are divided into two skin categories, the structure of which is quite different. What all masks have in common: The filtering layer made of meltblown, which is made in different layers and basis weights, depending on the application:
Standard EN 14683 Type I, II, IIR
Mouth-nose masks or so-called surgical masks primarily protect the environment from the wearer.
Standard EN 149 FFP 1-3
Respirators protect the wearer from infection. These masks are required by personnel who come into contact with people who are already infected. Only if the respirator does not have an exhalation valve, it also provides protection in the other direction.
All medical face masks are equipped with so called N95* and N99* meltblown nonwovens, whether they are face masks or respirator masks. Nevertheless, the nonwovens differ considerably from one another since the specifications are always linked to the size of the particles filtered. An N95 meltblown to filter building dust requires a different production process than an N95 meltblown to filter viruses.
Therefore, when ordering meltblown material, the filter performance required must be specified exactly as well as the intended purpose of the filter. It is not enough to specify simply N95 nonwoven or N99 nonwoven.
* The values N95 and N99 indicate the percentage of a specified particle size range absorbed by the material.