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dcyphr | Performance of fabrics for home-made masks against spread of respiratory infection through droplets: a quantitative mechanistic study

Abstract:


Respiratory infections such as Coronavirus Disease 2019 (COVID-19) can spread through droplets, airborne particles, and aerosols from speaking, sneezing, or coughing. The spread of the virus can come from presymptomatic, asymptomatic, or symptomatic individuals.The CDC has recommended home-made cloth face coverings for the general public. N95 respirators are the gold standard. Currently they are in short supply and should be reserved for the medical professionals. There is little research exploring the effectiveness of various mask materials. This study assesses the performance of ten different fabrics. The mask should as breathable without hurting the performance. Most single layer masks were found to block a considerable amount of droplets. When the mask is a two layer system it reaches the efficiency of a surgical mask while being easily breathable. Finally, it has been observed that home fabrics are hydrophilic. Meaning they readily soak of water. Whereas, medical masks are hydrophobic and tend to repel water. Homemade masks are hydrophilic. Meaning they tend to absorb incoming droplets. This could be a understudied advantage of homemade cloth masks.


Introduction:


Behind every pandemic is a disease causing agent that spreads globally. Current avenues for SARS-Cov2 are not entirely understood. Based upon knowledge from past infectious agents there appear to be three major routes of transmission. Large droplets can fall to surfaces due to gravity and can be a route for contact spread. Smaller droplets can travel in the air longer, and droplets inhaled directly into the lungs can easily enter the body. WIth various routes of infection the CDC recommends that the general public wear homemade cloth face masks. Existing research on home-made masks focuses on filtration efficacy against particles less than 1 micrometer in size. This is not helpful for SARS-Cov2 because the virus is several times smaller than that. A fabric with high breathability may have low blocking efficiency and vice versa. The ideal fabric would maximize breathability and blocking efficiency.. Therefore this study evaluates 10 different regular household fabrics: 100% cotton, 100% polyester, several ratios of cotton to polyester, used dishcloth, silk, and a 3 layered medical mask fabric.


Methods:



Five different qualities of the fabrics were analyzed:(1) Droplet blocking efficiency, (2) breathability, (3) weight, (4) hydrophilicity, (5) microscopic texture. To measure droplet blocking efficiency the researchers loaded a metered-dose inhaler with 100nanometer-diameter fluorescent beads to mimic the virus. The fabrics were placed over a petri dish by attaching the fabric cut-outs to the rim of the petri dish with double sided tape. The number of fluorescent beads captured vs the total number showed the droplet blocking efficiency of the fabric. Breathability was measured by observing the air flow rate and pressure created by a specified air flow rate. Special equipment was used throughout this experiment to test all parameters, but the researchers offer a simple home breathability test and droplet soaking test that offer a qualitative measurement of a fabrics breathability.


Results:


A Medical surgical mask provided a baseline blocking efficiency of 96.3% with a breathability of 2.5 mm/Pa*s. The fabric that offers the worst protection is a used T-shirt made from 75% cotton and 25% polyester. This fabric offers a blocking efficiency of 42.6%, with the highest breathability of 15.3 mm/Pa*s. Whereas, the fabric that offers the best blocking efficiency was a 3 layered New T-shirt made from 60% cotton and 40% polyester. This fabric offered a blocking efficiency of 99.98% and a breathability of 3.1 mm/Pa*s. The three layered T-shirt design offered a breathability and blocking efficiency higher than that of a standard surgical mask.


Discussion:


Breathability and particle blocking efficiency are important, but a balance must be made between these two parameters. If the mask is too breathable then blocking efficiency suffers heavily. If the mask is too restrictive then airflow will have to come from between the mask and the face of the person wearing it. This offers no true protection and the mask offers nothing more than a false feeling of protection. However, if the mask uses proper fabric like a 2 layer shirt mask, there will be a 98% blocking efficiency for low velocity droplets received from an infected individual. Therefore homemade 2 layer T-shirt masks may help prevent the spread of droplets from those infected to a healthy individual. The hydrophilicity of homemade masks does not discount them as effective and should be further researched as a potential benefit of understudied advantage. Therefore, the researchers of this study conclude that during pandemics, a home-made mask can be effective against transmission of infection through low-speed droplets. However, proper mask usage and education are as effective in accordance with social distancing rules and other preventive measures.