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The N97 grade polyacrylonitrile nanofiber mask demonstrates strong virus capture capability

Time : 2021-10-11 Hits : 17

In 2019, the Novel Coronavirus disease (COVID-19) broke out and quickly spread around the world. The diameter of COVID-19 virus currently discovered is 60-140 nm, and the main transmission routes are direct transmission, aerosol transmission and contact transmission. As a result, the demand for N95 class masks (N95 FFR) has increased dramatically. N95 class masks are mainly made of polypropylene (PP) melt-blown nonwovens. In order to improve filtration efficiency and maintain relatively low resistance, PP fibers are subjected to corona discharge methods to provide strong particle adhesion to the N95 FFR via static charge. However, charge can be lost during use, resulting in a decrease in filtering efficiency. In addition, reuse of the N95 FFR is restricted due to factors such as hygiene, damage, increased respiratory resistance and reduced filtration efficiency. In view of this, a team led by Yu Jihong of Jilin University developed a stable N97 nanofiber respirator based on chemically modified surfaces to achieve significant filtration characteristics through polar-driven interactions. It is achieved by coating polyacrylonitrile nanofiber membrane (TFPNM) at 0.42 PA-1 (filtration efficiency: over 97%; Pressure drop: approx. 10 Pa) provides overall durable filtration performance. Coxsackie B4 virus filtration test showed that TFPNM also has strong virus capture capability. Compared with N95 FFR, TFPNM is more resistant to a wider range of disinfection regimens (virus type: Coxsackie B4 virus (CV-B4) and a micro RNA virus), and overall filtration characteristics remain N97 standard. Related work is entitled "Polarity- Dominated Stable N97 respirators for Airborne virus Capture based on nanonanoous Membranes "was published in Angewandte Chemie, a top international journal.

Surface polarity and stability of TFPNMs

Thin film (TF) coated electrospun polyacrylonitrile (PAN) nanofiber membranes (TFPNMs) are manufactured by electrospinning technology and functionalized by interfacial polymerization processes to produce light yellow fabrics with variable end groups. Compared to PP, TFPNMs has a stronger surface polarity, which can be changed by different coatings. To further evaluate the stability of the TFPNM, the team tested the fiber membranes by exposing them to high temperatures (> 80 °C), a steam atmosphere (high humidity > 100 °C), 75% alcohol, chlorinated disinfecting water, and ultraviolet (UV) light. TFPNM was found to have no significant damage and weight loss, indicating no change in fiber geometry. Compared with the initial TFPNM, the surface polarity of the post-treated TFPNM remains unchanged. Stable surface polarity enables stable polar interactions between the membrane and PMs/ aerosols, giving TFPNMs great potential for reuse in a variety of harsh conditions.


Figure 1 Morphology and stability of TFPNMs

TFPNM air filtration efficiency

The researchers first examined TFPNMs's ability to capture particles of various sizes (PMs) to simulate its air filtration performance under hazardous air quality conditions (Figure 2). Burning incense (containing various pollutants such as PM, CO, CO2, NO2, etc.) is used in the laboratory to present levels of harmful particulate matter. The optimal base weight control for all TFPNM is 10 g/m2. The five TFPNMs with different surface polarities show great differences in filtration efficiency. The results of filtration efficiency for PM0.3 from the lowest surface polarity to the highest fiber membrane ranged from 50.00% to 97.45%. Among them, TFPNMs with cyanide and carboxyl groups showed very high filtration efficiency, exceeding 97%. To investigate the long-term efficacy of TFPNM, the mass status of TFPNM with the same terminal group as PAN molecule was tested after being placed in hazardous air for 10h. The results showed that the filtration efficiency of PAN nanofiber membrane (PNM) decreased from 97.10% to 94.57% for PM0.3 and from 99.67% to 99.42% for PM2.5 after 10 hours. However, the filtering characteristics of CTFPNM remained stable, exceeding 97.00% and 99.90% for PM0.3 and PM2.5 within 10 hours, respectively.


FIG. 2 PMs capture performance of TFPNMs with different surface polarities

Comparison of air filtration performance between TFPNM and N95 FFR

Two TFPNM with high surface polarity (CTFPNM and CTFPNM) were introduced to compare their filtration properties on NaCl aerosols with N95 FFR (Figure 3). The filtration efficiency of CTFPNM and CTFPNM both reached N97 level and remained stable during the continuous 24 hours of filtration. In contrast, the N95 FFR, which is mainly composed of charged PP melt-blown nonwovens, shows obvious instability during filtration. The filter efficiency of TFPNM was further studied by electrostatic effect. For charged cTFPNM and cTFPNM, their filtration efficiency is slightly improved to N98. However, the filtration efficiency of these charged respirator membranes eventually decreased to class N97 after 24 hours due to the attenuation of the surface static charge (from 0.15 kV to 0.02±0.03 kV). The author further studies the differences in air filtration characteristics between TFPNM and N95 FFRS from different countries. It was found that the filtration efficiency of all samples decreased to less than 95% after 24 hours of continuous filtration. Under the same experimental conditions, the filtration efficiency of N95 FFR was lower than that of cTFPNM after 24 hours.


Figure 3 Filter characteristics of TFPNMs and filter layers of multiple brands OF N95 FFRs

TFPNMs filtering efficiency for viruses and various disinfection treatments

CTFPNM was placed in coxsackie B4 virus (CV-B4) and a micro RNA virus aerosol (27-30 nm) to evaluate its filtration efficiency. And the N95 FFR (MEO brand) virus filtering test. The results showed that cTFPNM maintained N97 filtration efficiency after 24 hours, while MEO N95 FFR filtration efficiency dropped below 95% after 24 hours. In order to study the reusability of TFPNMs, five treatment methods were carried out for cTFPNMs: heat treatment at 80 ℃; Steam (heat base protein denaturation at 100 ℃); 75% alcohol (protein denatured); Household chlorine-based solution (cell degeneration, chemical damage); Ultraviolet germicidal irradiation (DNA/RNA destruction, UVC 254 nm). After the first treatment cycle, all filtration efficiencies of cTFPNMs remain unchanged at the LEVEL of N97 and the pressure drop remains between 9 and 10 Pa. In contrast, the N95 FFR showed different filtration performance after various treatments after the first cycle. Heating and ultraviolet germicidal irradiation (UVGI) maintain the filtration characteristics of most N95 FFRS. However, the filtration efficiency of samples based on solution treatment drops sharply to 50% ~ 80%.


FIG. 4 Virus filtering performance on cTFPNM

Note :(a) (b) is cTFPNM, (c) (d) is efficiency and pressure drop of meo brand N95 FFR


FIG. 5 Evolution of FFR and corresponding overall filtration performance after five different disinfection treatments

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