So far, covid-19 has been diagnosed in the US near 20 million. Although the number of confirmed cases has dropped by 12% in the last two weeks, the number of confirmed cases and deaths in Tennessee and Alabama has been cut. The rate of hospitalization in New York has reached the highest level since May 10th.

Now that the United States has injected 1.94 million doses of vaccine, why has their epidemic situation become more serious instead of alleviating?

covid-19 is a very important holiday for the United States. The new crown pneumonia is no longer serious and can not prevent their family reunion. On Christmas Eve, the train station has gathered many residents to go home. At Christmas, family gatherings are inevitable, and the number of confirmed cases is unavoidably on the rise.（click to share to linkedin）

According to the data released by the U.S. Transportation Safety Administration, on Christmas day alone, 616000 Americans went out to travel at the airport security check. The data shows that in the past few weeks, millions of people still went out to travel. In such a serious epidemic situation, there are so many people traveling, which will undoubtedly increase the spread and spread of coronavirus.

Another reason is that although the United States has injected nearly 2 million doses of the new crown vaccine, the people who are injected are health care workers and other high-risk groups, such as the elderly in nursing homes. In fact, this kind of population is not active and is not the main force of spreading the covid-19.（Click to share to Facebook）

Young people or middle-aged people in the United States are the main carriers of the virus, but these people have not been able to get vaccinated or refuse to get vaccinated for the time being, and they like to go out for dinner or travel. As a result, even if there is a covid-19 vaccine, it will still aggravate the spread of the covid-19 because the main communicators do not pay attention to it or take preventive measures.

Antony fudge, director of the National Institute of allergy and infectious diseases, told CNN that it is the darkest time in the United States.

Now the demand for masks in the United States is soaring. On the one hand, the number of confirmed cases is rising. On the other hand, in order to cope with the outbreak of the epidemic in winter, many states in the United States begin to force medical institutions to increase the inventory of masks and other medical protective equipment. New Jersey and New York require at least 90 days of inventory, and California also requires 45 days of inventory.（mask material is needed）

Due to the cumbersome certification process of FDA, many companies are unable to add new mask production lines, which limits the supply. At present, there are many areas in the United States with insufficient masks in stock, such as Michigan, where as many as two-thirds of medical institutions say that they can not protect users for three weeks, and some medical institutions will start to reuse masks again.

In the case of shortage of masks, people can only reuse masks. In order to avoid the failure or contamination of masks, we can only strengthen the disinfection of masks. The key of disinfection is to prevent the loss of static electricity.（meltblown machine is needed）

High temperature disinfection, what temperature is more appropriate?

The relevant team has also done research on the disinfection of masks. The masks were heat-treated for 100 minutes at different temperatures, and then the filtration effect was tested. The results are as shown in the figure. After 70 ℃, the filtration effect of the masks decreased slightly, while after 110 ℃, the filtration effect of the masks decreased to a large extent, which indicates that there are two kinds of charges in the masks, and the initial decay temperature is not high Same as. It can be seen that the suitable temperature for disinfection mask is about 70-80 ℃.

（Filtration performance of Beihua II meltblown membrane after heat treatment at different temperatures）

Can alcohol disinfect masks?

75% alcohol can effectively kill the virus, but alcohol can quickly eliminate the polypropylene charge of the mask. For example, alcohol immersion will greatly reduce the barrier capacity of the mask, as shown in the figure. Therefore, it is not appropriate to disinfect the mask with alcohol.

In fact, isopropanol, which belongs to the same alcohols as alcohol, has a stronger ability to remove the charge from the mask than alcohol. This is because the structure of isopropanol and polypropylene is closer, and it is easier to enter the polypropylene melt blown cloth and make close contact with the surface of the fiber, which enlarges the subspace through the swelling effect and makes the charge run away faster. In the test standard of ISO 16890 (general air filtration equipment), isopropanol is used to remove the charge in the filter screen to detect its pure mechanical filtration.

（Effect of hot water and alcohol disinfection on filtration performance of Beihua II mask）

Is it possible to disinfect the mask with hot water?

Due to the poor affinity of water to polypropylene, it is possible to ensure the stable existence of electric charge after killing the virus with water at a certain temperature. Due to the influence of temperature on the charge dissipation, the research team tested the wet steaming mask in the steamer and the hot water immersion mask in the temperature range of 60-80 ℃. These two methods are suitable for household use.

The results show that the mask can maintain better filtration efficiency than alcohol after repeated treatment in wet steaming and hot water for 10 times, and the retention rate of hot water disinfection is higher than that of wet steaming disinfection (as shown in Figure 17), because the temperature of hot water is lower than that of steam. So masks can be disinfected with hot water.

（Effect of hot water immersion and wet steaming on filtration performance of Beihua III meltblown membrane）

Will wearing a mask reduce the filtering effect?

The mask will accumulate a certain amount of water when wearing, and the ion concentration in the water will be higher, which may dissipate the electric charge in the mask; the particles in the air may also digest part of the electric charge in the mask when they are constantly intercepted by the mask fiber; the repeated breathing and taking off in the wearing process may also have an impact on the local pore expansion of the fiber accumulation structure.

In the experiment, it is found that the filter efficiency of the mask after wearing is obviously decreased (as shown in the figure), and it varies from person to person, resulting in large dispersion of filter efficiency data. In other words, the wearing behavior has a significant impact on the filtering performance of the mask. Therefore, in the process of mask reuse, it is necessary not only to choose the mask with high initial filtration efficiency, but also to fully consider the retention ability of filtration efficiency after wearing.

（Changes of filtration efficiency of a brand mask and Beihua III-1 mask before and after wearing for 24 hours）

Can I use a hair dryer to blow the mask?

Although the affinity between polypropylene fiber and water is very poor, the electrostatic adsorption capacity of polypropylene melt blown cloth may be affected by human breath during wearing. It is recommended to wear the mask for no more than 4 hours at a time. If it needs to be worn after 4 hours, it needs to be dried. Drying treatment is not only a process of removing moisture, but also a process of recovering or regenerating the electrostatic adsorption property of EPDM meltblown cloth.

Natural air drying or electric hair dryer can be used for drying. The electric hair dryer can quickly remove moisture and restore the electrostatic adsorption capacity of fibers. It is recommended to use this method for people who wear masks for more than 4 hours a day, people who wear masks in wet areas and wet weather, and heavy manual workers.

In fact, the best way to disinfect masks is UV disinfection. Suntech integrated mask machine has been used to disinfect the mask by UV when it is producing the mask. Of course, this function can also be used to disinfect the mask repeatedly in the future.

（ST-AMM mask machine,Click to contact）