Regulation of polylactic acid using irradiation and preparation of PLA–SiO2–ZnO melt-blown nonwovens for antibacterial and air filtration† † Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d2ra08274h

Since the COVID-19 pandemic, polypropylene melt-blown nonwovens (MBs) have been widely used in disposable medical surgical masks and medical protective clothing, seriously threatening the environment. As a bio-based biodegradable polymer, polylactic acid (PLA) has attracted great attention in fabricating MBs. However, there are still issues with the undesirable spinnability of PLA and the limited filtration and antibacterial performance of PLA MBs. Herein, a high-efficiency, low-resistance, and antibacterial PLA filter is fabricated by melt-blown spinning and electret postprocessing technology. The irradiation technique is used to tune PLA chain structure, improving its spinnability. Further, silica (SiO2) nanoparticles are added to enhance the charge storage stability of PLA MBs. With a constant airflow rate of 32 L min−1, the PLA-based MBs exhibit a high particulate filtration efficiency of 94.8 ± 1.5%, an ultralow pressure drop of 14.1 ± 1.8 Pa, and an adequate bacterial filtration efficiency of 98 ± 1.2%, meeting the medical protective equipment standard. In addition, the zinc oxide (ZnO) masterbatches are doped into the blend and the antibacterial rate of PLA-based MBs against Escherichia coli and Staphylococcus aureus is higher than 99%. This successful preparation and modification method paves the way for the large-scale production of PLA MBs as promising candidates for high-efficacy and antibacterial filters. PLA MBs with high filtration efficiency and antibacterial activity were prepared by reducing viscosity by irradiation and blending ZnO and SiO2.

Regulation of polylactic acid using irradiation and preparation of PLA-SiO2-ZnO melt-blown nonwovens for antibacterial and air filtration.

Since the COVID-19 pandemic, polypropylene melt-blown nonwovens (MBs) have been widely used in disposable medical surgical masks and medical protective clothing, seriously threatening the environment. As a bio-based biodegradable polymer, polylactic acid (PLA) has attracted great attention in fabricating MBs. However, there are still issues with the undesirable spinnability of PLA and the limited filtration and antibacterial performance of PLA MBs. Herein, a high-efficiency, low-resistance, and antibacterial PLA filter is fabricated by melt-blown spinning and electret postprocessing technology. The irradiation technique is used to tune PLA chain structure, improving its spinnability. Further, silica (SiO2) nanoparticles are added to enhance the charge storage stability of PLA MBs. With a constant airflow rate of 32 L min-1, the PLA-based MBs exhibit a high particulate filtration efficiency of 94.8 ± 1.5%, an ultralow pressure drop of 14.1 ± 1.8 Pa, and an adequate bacterial filtration efficiency of 98 ± 1.2%, meeting the medical protective equipment standard. In addition, the zinc oxide (ZnO) masterbatches are doped into the blend and the antibacterial rate of PLA-based MBs against Escherichia coli and Staphylococcus aureus is higher than 99%. This successful preparation and modification method paves the way for the large-scale production of PLA MBs as promising candidates for high-efficacy and antibacterial filters.

COVID-19 prevention and control in China: grid governance.

The coronavirus disease 2019 (COVID-19) pandemic has spread worldwide and caused negative economic and health effects. China is one of the most seriously affected countries, and it has adopted grid governance measures at the basic level of society, which include city lockdown, household survey and resident quarantine. By the end of April, China had basically brought the pandemic under control within its own borders, and residents' lives and factory production gradually began to return to normal. In referring to the specific cases of different communities, schools, and enterprises in the four cities of Anhui, Beijing, Shenzhen and Zibo, we analyze grid-based governance measures and we summarize the effectiveness and shortcomings of these measures and discuss foundations and future challenges of grid governance. We do so in the expectation (and hope) that the world will gain a comprehensive understanding of China's situation and introduce effective measures that enable the prevention and control of COVID-19.

Propagation analysis and prediction of the COVID-19 (preprint)

Based on the official data modeling, this paper studies the transmission process of the Corona Virus Disease 2019 (COVID-19). The error between the model and the official data curve is within 3%. At the same time, it realized forward prediction and backward inference of the epidemic situation, and the relevant analysis help relevant countries to make decisions.

Propagation analysis and prediction of the COVID-19 (preprint)

Based on the official data modeling, this paper studies the transmission process of the Corona Virus Disease 2019 (COVID-19). The error between the model and the official data curve is within 3%. At the same time, it realized forward prediction and backward inference of the epidemic situation, and the relevant analysis help relevant countries to make decisions.