Meltblown is just a good material for filters

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Meltblown is just a good material for filters

The main purpose of this type of material is to ensure the safety of respirators and medical protective clothing. Face masks and medical protective clothing are made of non-woven material. The meltblown (in the form of one of the functional layers) acts as a filter and performs its main function - highly efficient separation and retention of the smallest particles, such as bacteria and viruses.

Meltblown is a nonwoven fabric made of extremely thin microfibres extruded from a polymer melt and formed through a die by blowing them in a hot air environment and then laying on a conveyor belt or drum. Such fibers are seventy times thinner than a human hair, and a single fiber sometimes has an average thickness of only one micron. The raw materials used for the manufacture of meltblown are polymers - polypropylene is usually used for the manufacture of face masks.

meltblown nonwoven fabric - production technology and fiber structure

Good filters skip only what is needed. This task becomes more difficult the smaller the size of the particles that need to be filtered. The simple sieve effect is no longer effective for separating very small particles such as viruses and bacteria. For example, in the case of face masks, an additional combination of effects, such as inertial action, diffusion and electrostatic attraction, acts simultaneously.

The sieve effect: particles larger than a certain size are captured by the mesh structure of the material.

Inertia effect: larger particles cannot bend around the filter fibers in the air stream. They keep their direction, hit the fiber and stick to it.

Diffusion: very small particles, such as viruses, often move in the air stream along incorrect trajectories (Brownian motion). This leads to a high probability of contact of particles with filter fibers.

Electrostatic attraction: To enhance the effect of diffusion and inertia, materials are charged electrostatically to filter the smallest particles. Then the filter fibers attract the particles like a magnet and trap them.

meltblown nonwoven fabric is a good filter material

What is a good filter?

  • High filtration efficiency: the maximum number of particles is retained in the filter.
  • Low pressure drop: it is easy to breathe through the filter.
  • High absorption capacity: The maximum possible amount of particles can be absorbed before the filter becomes clogged and the pressure drop increases. Moisture in the breath reduces the filtering capacity, which is why filters need to be replaced regularly.
  • Low cost: Filter media are often a functional layer of a multi-layered disposable product.

Why is meltblown an ideal filter material?

  • Nonwovens blown from the melt consist of extremely thin fibers, with an average thickness of 1 microns and infinite length. For comparison, cotton fiber has a thickness of 12–35 microns and a length of 15–56 mm.
  • Meltblown nonwovens are produced in different thicknesses and densities. Example: nonwoven fabric with a density of 25 g/m2 consists of max. 500 layers of fiber.
  • Due to its structure and additional electrostatic charge, all the filtering effects in the meltblown act simultaneously. Even the smallest particles that may contain coronavirus are reliably captured.
  • Filters made of meltblown combine high performance with good wearing comfort (easy to breathe), since the right balance between filtration efficiency, absorption capacity and pressure drop can be realized.
  • The material is inexpensive and can be produced quickly in large quantities.

What is the design of masks and respirators?

There are many different medical masks. They are basically divided into two main categories with clear design differences. What all masks have in common: a filter layer made of meltblown, which is applied in the form of one or more layers and has a certain density, depending on the application of the finished product:

Face masks (standard EN 14683, types I, II, IIR)

Face masks, also known as surgical masks, primarily protect the user from the environment.

Construction:

  • nose clip
  • ear loops
  • spunbond
  • meltblown
  • spunbond

Respiratory masks (standard EN 149 FFP 1-3)

Respiratory masks protect the wearer from infection. These masks are required by personnel who come into contact with people who are already infected. They also provide protection in the opposite direction if the respirator is not equipped with an exhalation valve.

Construction:

  • thermoformed rigid respirator base (optional)
  • nose clip
  • ear loops
  • spunbond type nonwoven fabric
  • meltblown
  • meltblon
  • activated carbon fabric (optional)
  • meltblown (optional)
  • spunbond type nonwoven fabric
  • exhalation valve (optional)

All medical masks, whether face masks or respirators, are equipped with so-called non-woven materials N95 and N99. The values N95 and N99 indicate the percentage of particles of a certain size absorbed by the material. However, nonwovens differ significantly from each other, since the characteristics of the material are always related to the size of the filtered particles. The production of Class N95 meltblown for filtering construction dust requires different process settings than the production of N95 meltblown for filtering viruses.

Thus, when purchasing the material blown out of the melt, it is necessary to specify exactly the required filtration efficiency, as well as the intended scope of the filter. It is not enough to specify just nonwoven fabric N95 or nonwoven fabric N99.

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