Due to the overwhelming demand, we retooled out factory towards medical supplies and apparel.
Therefore we are able to offer face masks for general public at our cost (*we are still cutting and sewing each masks individually so we can not produce at China prices).
Please see the following recommendation from The National Academies of Science Engineering Medicine
*FILTRATION THEORY OF AIRBORNE PARTICLES
Media used for the filtration of airborne particles do not work by the same principles as those used for the filtration of liquids. Filters used in respirators and medical masks must allow the user to breathe and thus cannot clog when particles adhere to their fibers. Respirator and medical mask filters are typically composed of mats of nonwoven fibrous materials, such as wool felt, fiberglass paper, or polypropylene (see Box 2-1). The material creates a tortuous path, and various mechanisms result in the adhesion of particles to the fibers without necessarily blocking the open spaces, still allowing air to flow easily across the filter (Revoir and Bien, 1997).
This chapter will discuss three mechanisms of removing particles from the airstream: inertial impaction, diffusion, and electrostatic attraction (see Figure 2-1). Mechanisms for removing large particles differ from those for small particles.
The model postulates that inertial impaction is effective for aerosol particles that are approximately 1 μm and larger. Such particles have enough inertia that they cannot easily flow around the respirator fibers. Instead of flowing through the filter material, the large particles deviate from the air streamlines and collide with the fibers and may stick to or be caught in them.
For much smaller particles—those that are 0.1 μm and smaller— diffusion is regarded as an effective filtration mechanism. Brownian motion—the process by which the constant motion of oxygen/nitrogen molecules causes collisions between particles—results in a “wandering” pathway. The complex path that is followed by the small particles increases the chance that they will collide with the filter fiber and remain there.
Another efficient method of capturing both large and small particles from the airstream is said to be electrostatic attraction, in which electrically charged fibers or granules are embedded in the filter to attract oppositely charged particles from the airstream. The attraction between the oppositely charged fibers and particles is strong enough to effectively remove the particles from the air. The first electrostatic filters used resins
Copyright National Academy of Sciences. All rights reserved.
Reusability of Facemasks During an Influenza Pandemic: Facing the Flu
24 REUSABILITY OF FACEMASKS DURING AN INFLUENZA PANDEMIC
Materials and Components Used in Respirators and Medical Masks
The filtering materials of respirators and medical masks are typically nonwoven. These materials, initially using natural fibers, came into greater prominence with the introduction of synthetic thermo- plastics, particularly polypropylene, about 40 years ago. Spun- bonded polypropylene is a fabric or structure in the category of nonwoven textile materials. The salient advantage of nonwoven technology is the ability to produce fabrics or structures at significantly lower cost than the older fabric-generating techniques of weaving or knitting of spun yarns. Additional important advantages are the versatility of the process and the products in terms of properties and uses. There has been ongoing development of and in- creasing sophistication in spun-bonded, and the related melt blown, technologies, which have made these materials the optimal choice in many applications.
Polypropylene is one of five major commodity plastic resins now produced in large quantities in many countries. It is readily con- verted into spun-bonded fabric and structures with a very wide range of properties. Some of the parameters that can be varied include fiber thickness (down to micron or submicron diameters), density of fibers per unit area or volume, density of bond points, and average orientation of fibers.
For filtration and trapping of aqueous particles (as in respirators and medical masks), polypropylene fiber surfaces require modification to render them more hydrophilic (water attracting) because polypropylene is inherently hydrophobic (water repelling). Several methods are known to impart the necessary degree of hydrophilic- ity to the surface. A process in which a droplet-attracting electric charge is applied to the surface has also been described, but it is not clear that such a charge could be maintained during storage of the respirator or mask, and the charge would dissipate with expo- sure to air with any degree of humidity.
These materials and processes have produced a viable material whose low cost permits a disposable, one-use culture to prevail in industrialized countries. Spun-bonded polypropylene masks have completely supplanted the woven cotton fabric masks previously used in the United States and predominate in the filtration components of commonly used respirators.
Copyright National Academy of Sciences. All rights reserved. Reusability of Facemasks During an Influenza Pandemic: Facing the Flu CHARACTERISTICS OF RESPIRATORS AND MEDICAL MASKS 25
FIGURE 2-1 Filtration mechanisms.
added to natural wool fibers to retain an electrostatic charge. This addition enhanced the efficiency many times over the basic wool material. However, the efficiency of resin electrostatic filters is degraded when they are exposed to airborne oil mists and other materials that shield the electrostatic charge. Manufacturers have been able to overcome this issue by incorporating synthetic plastic fibers, such as polypropylene (see Box 2-1), which are said to be capable of holding a sufficiently strong electrostatic charge (electret) to effectively resist the shielding effects of oil. Once particles are captured by a filter, they are held tightly to the fibers through van der Waals bonding and other forces, thus making it difficult for captured particles to escape. Filters generally become more efficient with loading (i.e., the adhesion of additional particle to the filter fibers). This increase in efficiency is the result of the increased number of collection points that are created by the particles that have already adhered to the filter fibers. However, increased loading becomes a problem when enough particles have been captured to begin to block the open spaces of the woven or nonwoven network. This blockage results in a buildup in pressure drop