SMS Non Woven Production line in India
Masks have now become a must-have item for everyone. Everyone’s awareness of wearing masks has also “increased” significantly. The materials of protective masks are mostly non-woven fabrics, also known as non-woven fabrics, which are composed of directional or random fibers. It is called cloth because it has the appearance and certain properties of cloth.
What are the material science reasons behind the uses of different types of masks?
Extending it further to personal protective equipment (PPE), what special polymer materials and manufacturing processes are involved behind it?
The mask is divided into four layers. The outer two layers are two pieces of cloth-like material. The black one is the activated carbon layer. There is also a layer of denser material with a texture similar to a napkin. After consulting some information, the editor learned that except for the activated carbon layer in the middle, the other three layers are made of a material called non-woven fabric. Non-woven fabrics are composed of directional or random fibers. It is called cloth because it has the appearance and certain properties of cloth.
There are many manufacturing processes for non-woven fabrics, including spunbonding, melt-blown, hot rolling, spunlace, etc. The raw materials that can be used are mainly polypropylene (PP) and polyester (PET). In addition, there are nylon (PA), viscose fiber, acrylic fiber, ethylene fiber (HDPE), chlorine fiber (PVC), etc
Most of the non-woven fabrics on the market today are produced by the spunbond method. In this method, the polymer is extruded and stretched to form continuous filaments. The filaments are then laid into a web, and the web is then bonded to itself. Thermal bonding, chemical bonding or mechanical reinforcement methods turn the fiber web into a non-woven fabric. It is easier to identify spunbond non-woven fabrics. Generally, the nip points of spunbond non-woven fabrics are diamond-shaped.
The middle layer of general surgical masks uses non-woven fabric made by melt-blown method.
The production of melt-blown non-woven fabrics is to first put the polymer masterbatch (usually polypropylene) into the extruder and melt it in the extruder at a temperature of about 240°C (for PP). The melt passes through the metering pump and reaches the melt-blown die head. When the newly formed polymer is extruded from the spinneret, the head end of the compressed air acts on the polymer, drawing the hot filament to a diameter of 1~10μm with an air flow higher than the speed of sound (550m/s), according to its physical properties. This kind of mesh is called microfiber mesh. These ultrafine fibers with a unique capillary structure increase the number and surface area of fibers per unit area, thus making the melt-blown cloth have good filtering, shielding, thermal insulation and oil absorption properties. It can be used in air, liquid filter materials, isolation materials, mask materials and other fields.
The filtration mechanism of medical masks is Brownian diffusion, interception, 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%; this cannot meet the requirements of medical masks. We need to electret the material to allow the fibers to It is charged and uses static electricity to capture the aerosol where the new coronavirus is located.
Electrostatic adsorption is the capture of COVID-19 droplets (aerosols) through the Coulomb force of charged fibers. The principle is to make the surface of the filter material more open, and the ability to capture particles is stronger. As the charge density increases, the adsorption and polarization effect on particles is stronger. Therefore, the melt-blown non-woven filter material of the filter layer must go through a stationary process. Only with extreme treatment can 95% filtration be achieved without changing the breathing resistance, and the virus can be effectively prevented.
