The global supply of medical protective grade N95 masks (later referred to as N95 masks) has been under strain since the outbreak of the New Coronavirus outbreak. In such a situation, whether N95 masks can be disinfected and reused becomes a very real issue. If so, which disinfection measures should be taken and how many times can N95 masks be reused at most?
A research team led by Yi Cui, a professor in the Department of Material Science and Engineering at Stanford University, disinfected the meltblown fabric, the core component of the N95 mask, in different ways and evaluated the changes in virus blocking ability and structural integrity of the meltblown fabric treated with different disinfection methods by testing the filtration efficiency and filtration resistance.
The results showed that high temperature treatment within a certain humidity range and UV irradiation were the two most promising methods for disinfection of N95 masks. Treatment with these two methods 20 times did not significantly reduce the filtration efficiency and filtration resistance of the meltblown cloth.
The N95 mask is designed to filter sodium chloride aerosols with a diameter of 0.3 μm with an efficiency of more than 95%. Its core filter layer, meltblown fabric, is sandwiched between the surface moisture-resistant layer and the inner skin-fitting layer, and is made of ultra-fine polypropylene fibers with a diameter of <5 μm by a meltblown process. At the same time, the meltblown fabric undergoes electrostatic treatment (a method to increase fiber static electricity), so that the surface of the polypropylene fiber is charged with a large amount of electrostatic charge, which is used to adsorb and capture fine particles to improve the filtration efficiency.
The disinfection of N95 masks for reuse requires at least two criteria: 1. the effective killing of viruses attached to the mask; 2. the structure of the mask remains intact and the filtration efficiency is not reduced.
In layman's terms, it is best to disinfect a mask without getting it wet, otherwise the filtering function of the mask will be significantly reduced even if it looks intact.
After excluding the two disinfection methods of 75% ethanol soaking and 2% sodium hypochlorite solution spraying, the researchers treated the meltblown cloth with high temperature, water vapor and UV irradiation in multiple cycles to simulate the realistic multiple disinfection reuse situation. The results showed that the filtration efficiency of the meltblown cloth decreased dramatically after five treatments with water steam, but the integrity of the meltblown cloth did not change.
Interestingly, the 75°C treatment did not change the filtration efficiency and filtration resistance of the meltblown cloth, regardless of the high or low relative humidity of the disinfection environment (0, 30% and 100% relative humidity, respectively). Even 50 dry baking treatments at 75°C did not significantly affect the main structure and filtration performance of the meltblown fabric.
However, if the temperature reaches 125°C (relative humidity <30%, 10 min/round), the filtration efficiency of meltblown fabric will be sharply reduced after about 5 rounds of treatment.
The information is provided by the N95 mask supplier.