SINCE 1999

About the chemistry of masks

(2020-0408)

The new corona virus struck, and masks became a necessity for residents. What is the difference between disposable medical masks, medical surgical masks and medical protective masks (N95 masks)? What chemistry knowledge is included in it?

 

There is no doubt that our common masks are ordinary cotton masks, disposable medical masks, medical surgical masks, N95 masks ..., among which disposable medical masks, medical surgical masks can prevent respiratory infections to a certain extent, and are not anti-fog; N95 masks can effectively prevent respiratory tract infections and can prevent haze; ordinary cotton masks can not solve the purpose of preventing infections because the material itself is not dense enough.

 

Next, let's talk about disposable medical masks, surgical surgical masks and medical protective masks (N95 type masks)!

Disposable medical mask

Disposable medical masks use 2-3 layers of non-woven fabric as the filter material of the mask, mainly to prevent infection between doctors and patients or medical staff to inhale pathogens in the environment and be infected. The outer layer of the mask is water-resistant, which reduces the risk of the wearer being exposed to pathogens in the patients blood or fluid.

Non-woven fabric: The exact name of non-woven fabric should be non-woven fabric, or non-woven fabric. Because it is a kind of fabric that does not require spinning and weaving, it is simply oriented or randomly arranged textile short fibers or filaments to form a web structure, which is then reinforced by mechanical, thermal bonding or chemical methods. Non-woven fabrics break through the traditional textile principles, and have the characteristics of short process flow, fast production speed, high output, low cost, wide use, and many sources of raw materials. Medical non-woven products are medical and hygienic textiles made of chemical fibers including polyester, polyamide, polytetrafluoroethylene (PTFE), polypropylene, carbon fiber and glass fiber.

 

Protective performance

Ordinary-grade medical masks have many names. Medical masks without the words "protection" or "surgical" on their names are ordinary-grade medical masks. Masks of this level generally do not require a blocking effect on blood, so they are only used in general medical environments.

 

Medical surgical mask
Standard surgical masks generally consist of 3-4 layers. The outer layer has a waterproof effect to prevent droplets from entering the mask. The middle layer functions as a filter. The inner layer near the nose and mouth is used to absorb moisture to ensure that the wearer's lips are dry and comfortable. The filter element generally uses ultrafine fibers as the melt-blown nonwoven material, and the ultrafine fibers are randomly arranged to form a large number of tiny pores. The entire mask adopts a foldable design to improve the closeness of the mask and the wearer's face, and can block more than 90% of 5μm particles.

 

Superfine fiber: Definitions vary, also known as microfiber, fine denier fiber, ultrafine fiber. Generally, the fiber with a fineness of less than 0.3 denier (diameter 5 microns) is called ultrafine fiber. The main components are polyester polyester and nylon polyemide. Two compositions.

The process of melt-blown non-woven fabric: polymer feeding-melt extrusion-fiber formation-fiber cooling-netting-reinforcement into cloth.

 

Protective performance

Medical surgical masks are medical masks commonly used in operating rooms and other environments where there is a risk of body fluids and blood splashes. They can block blood and body fluids from passing through the mask to contaminate the wearer. At the same time, the filtration efficiency of bacteria should not be less than 95%, but the filtration efficiency of particles , And the tightness with the face is not as tight as medical protective masks.

The medical surgical mask is composed of three parts, from the outside to the inside are the waterproof layer, the filter layer, and the comfort layer. The white non-woven fabric faces inwards while the blue waterproof layer faces outwards.

 

Blocking principle:

Outer waterproof layer: usually needle-punched cotton also called polyester needle-punched felt, the polyester material itself is difficult to absorb water, and then the polyester staple fiber is made into non-woven fabric by needle punching, it is difficult to polar water molecules and droplets Through, non-polar air can be smoothly inhaled.

Middle filter layer: The main material of the melt-blown non-woven fabric is polypropylene, which is an ultra-fine and electrostatic fiber cloth that can capture droplets and dust. This layer of non-woven fabric is made of countless ultra-fine and electrostatic short fibers, which are interwoven and intertwined by mechanical force. The droplets and dust in the jungle composed of short fibers are like walking through a maze. In the electrostatic force and van der Waals force Under the action, most of them stumbled and adhered to the dense short fibers, thus playing a very strong adsorption effect.

Inner layer Comfort layer: It is a hot-rolled non-woven fabric, but its moisture absorption and breathability are much better than the other two layers. It mainly guarantees that the nose and mouth are moist and improves the wearing comfort.

 

SMS structure diagram of common masks

Medical protective mask

Also known as N95 mask, N means that this mask is suitable for use in non-oily occasions, 95 means that this mask can filter out more than 95% of fine dust with a volume of ≥0.3μm during use. The face mask is divided into inner, middle and outer layers, the inner layer is ordinary sanitary gauze or non-woven fabric, the middle layer is ultra-fine polypropylene fiber melt-blown material layer, and the outer layer is non-woven fabric or ultra-thin polypropylene melt-blown material Floor. This high-efficiency medical protective mask is highly hydrophobic and breathable, and has a significant filtering effect on tiny virus-containing aerosols or harmful fine dust. The overall filtering effect is good, and the materials used are non-toxic and harmless, and comfortable to wear.

Polypropylene fiber: Polypropylene fiber is a synthetic fiber spun from isotactic polypropylene obtained by polymerizing propylene, and its trade name in China is polypropylene. (Did you think of the simple structure of polypropylene in organic chemistry?)

 

Aerosol: a sol formed by dispersing solid or liquid (also called dispersed phase) and gas as dispersion medium. It has colloidal properties, such as light scattering, electrophoresis, Brownian motion and other characteristics. The solid and liquid particles in the atmosphere are in Brownian motion and do not settle due to gravity. They can be suspended in the atmosphere for months and years.

Mixed dispersion system: Dispersing one or several substances in another substance constitutes a dispersion system. Among them: the dispersed substance is called dispersed phase (dispersed phase); the other substance is called dispersing medium (dispersing medium). Such as: brine, sugar water, milk, clouds, etc.

 

Protective performance


The N95 mask is one of the nine anti-particulate masks certified by NIOSH (National Institute of Occupational Safety and Health). The biggest feature is that it can prevent droplet infection caused by patients.

classification

There are two common N95 masks, with and without a breathing valve. Breathing valves are believed to reduce the protection against viruses. Without breathing valves, breathability is poor and breathing is laborious and should not be worn for long periods.

 

 

Of course, after the mask is produced, there is still analysis and disinfection. It is not that the machine can be used directly after production and processing! Medical masks are sterilized with ethylene oxide! After sterilization, through analysis, the residual medicines are released to achieve safety standards!

Ethylene oxide: It is an organic compound with the chemical formula C2H4O. It is a toxic carcinogen and was previously used to make fungicides. Ethylene oxide is flammable and explosive, and is not easy to transport for long distances, so it has strong regional characteristics. It is widely used in washing, pharmaceutical, printing and dyeing industries. It can be used as a starting agent for cleaning agents in the chemical industry.

Schematic diagram of the molecular structure of ethylene oxide

The difference between KN95 and N95

The standards of N95 and KN95 are both non-oily particulate filtration efficiency ≥95%, so in essence, the protective effects of these two masks are the same, there are differences in certification bodies, N95 is the US NIOSH certification, and KN95 is the domestic certification , In line with China's GB2626 standard requirements.