Common medical masks are mainly composed of three layers of non-woven fabrics. The inner layer is an ordinary non-woven fabric; the outer layer is a non-woven fabric with a waterproof treatment, which is mainly used to isolate the liquid sprayed by the patient; the middle filter layer is an electret treatment polypropylene melt-blown non-woven fabric; Finally, after the production is completed, it must be disinfected with ethylene oxide and stand for 7 days to volatilize toxicity. After the production is completed, it is sealed and packaged and shipped away.
The core material of medical masks is polypropylene melt-blown non-woven fabric after electret treatment, which is the key to filtering coronavirus aerosols.
1. The raw material: polypropylene (PP) particles
Polypropylene is refined from crude oil through a series of chemical reactions.
2. Polypropylene fiber production
Just like textiles require plant fibers, the production of non-woven fabrics also requires fiber materials. Polypropylene particles are used to melt and shape for producing high melt index polyethylene fiber material, which is the core raw material for the production of masks.
3. Meltblown non-woven fabric production
Melt blowing is a polymer extrusion non-woven process. The process principle is to use high-speed hot air to draw the thin stream of polymer melt extruded from the die orifice, thereby forming ultra-fine fibers and Condensed on the condensation net curtain or roller, relying on self-bonding to become a non-woven fabric. The melt-blown material is made of its own fibers by heat melting, and the thicker melt-blown non-woven fabric is produced by the melt-blown method. The random fibers and interlayers are arranged to form a multi-curved channel structure of the melt-blown material so that the particulate matter and the fiber Struck by collision.
Tips: The filtering mechanism of medical masks is Brownian diffusion, retention, inertial collision, gravity sedimentation, and electrostatic adsorption. The first four are all physical factors, which are the natural characteristics of non-woven fabrics produced by the melt-blown method. The filterability is about 35%; but this does not meet the requirements of medical masks, so we need electret treatment.
For the protection principle of masks, you could check our article: “How does a mask protect you?“
4. Electret Treatment
Electrostatic adsorption is the capture of coronavirus droplets (aerosols) through the Coulomb force of charged fibers. The principle is to make the surface of the filter material more open, the ability to capture particles can be grabbed, and the charge density increases, and the particle adsorption and polarization effects are stronger. Therefore, the melt-blown non-woven filter material of the filter layer must be Electret Treatment, it can achieve 95% filterability without changing the respiratory resistance to effectively prevent viruses.
5. Masks production line
After the production of raw materials is completed, mask production is nothing more than simple machine processing.
6. Ethylene oxide disinfection
If it is an ordinary mask, it does not need to be disinfected, but a medical mask needs to be disinfected with an ethylene oxide (EO) disinfection cabinet. Put the masks in a 400mg/L ethylene oxide environment, and use alkylation to act on the hydroxyl group to inactivate the microbial macromolecules and achieve the purpose of sterilization.
However, ethylene oxide is not only flammable and explosive but also toxic to the human body. Therefore, it needs to stand for 7 days after disinfection. After the EO residue is lower than the required value, it can be packaged and delivered.