Dottorato in MODELLI MATEMATICI PER L'INGEGNERIA, ELETTROMAGNETISMO E
NANOSCIENZE

Titolo della tesi: Photocatalytic antibacterial activity and filtration performance of PVDF-HFP@TiO2 electrospun nanofibers membrane for medical face mask applications

Face masks have proven to be a useful protection from airborne viruses and bacteria, especially in the recent years ‘pandemic outbreak’ when they effectively lowered the risk of infection from Coronavirus disease (COVID-19) or Omicron variants, being recognized as one of the main protective measures adopted by the World Health Organization (WHO). The ability of viruses to coalesce with both large particles, ranging in size between ~2.5–10 μm, and the smaller ones due to pollution, with diameters smaller than 1 μm, which are present in the atmosphere, makes them extremely infectious. This is especially true for close-distance contacts, where the respiratory infection can be transmitted in a short period from an infected person to a healthy one during talking, coughing, and sneezing, and it can also remain suspended in the air for a long time, before spreading at longer distances. In this perspective, commonly used face masks, such as surgical and filtering half-masks (i.e., Filtering Face Pieces (FFPs)), turned out to be essential barriers to protect the wearer from submicron particles and biological contaminants that can be present in the form of droplets or aerosols in the atmosphere, reducing the spreading of and infection by coronavirus (SARS-CoV-2), for example. In order to determine the effectiveness of these face devices in preventing users from being infected by large and small droplets, which can be potential bacteria or virus carriers, the European Norm (EN) specifies several performance filtration criteria, which include Bacterial Filtration Efficiency (BFE) and Particle Filtration Efficiency (PFE). Within the unrecognized standard parameters, the Viral Filtration Efficiency (VFE) is a useful tests to add, since it employs the same procedure and setup as recommended by EN 14683 for BFE, but using a virus aerosol as a nonhazardous virus surrogate for SARS-CoV-2, instead of bacterial suspension, to quantify the degree of protection of face devices. Despite most of the commercial face masks are expected to effectively remove submicron particles present in the surroundings, the filter materials used are not able to inactivate both bacteria and viruses, thus making the utilization of these face devices disposable and very unsafe when they have been worn for a longer period than that recommended. An evident proliferation of fungi and bacteria were observed in common face masks after prolonged use, because of the moist air expired and inspired, thus representing a health risk especially in severe cases of illness. Therefore, the disinfection performance of disposable masks has become a relevant issue from the start of the pandemic, in order to avoid the risk of further contamination in the long run caused by the improper and continuous accumulation of waste masks into the environment. The layers forming a commercial filter media are mainly produced by means of the Melt-Blowing (MB) method and are generally composed of Polypropylene (PP), i.e., a thermoplastic polymer, whose fiber diameters are about the submicron size. Unlike MB, the Electrospinning (ES) method proved to be a promising technique to customize a broader range of synthetic and natural polymer-based electrospun membranes with fiber diameters and pore sizes down to the nanoscale, providing remarkable performance in both Particulate Matter (PM) capture and low pressure drop. Furthermore, the implementation of active metal oxide Nanoparticles (NPs), as well as other bioactive hybrid nanocomposites in polymer-based electrospun nanofiber filters, have proven to be advantageous to design environmental-friendly face masks with tailored filtration performance as well as photocatalytic properties, which makes them able to deactivate both bacteria and viruses after an exposure to light sources, and thus extending the lifetime quality of the device and making it reusable. The research activity presented in this Ph.D. thesis is focused on the assessment of the filtration performance of both the pristine and hybrid filtering polymer-based electrospun membranes, and their characterization by means of techniques typical of nanotechnology, including microscopy and spectroscopy methods. This Ph.D. grant was financed by both the Region Lazio and LABOR s.r.l. research industry funds in the framework of the program of initiatives “Intervento per il rafforzamento della ricerca nel Lazio - incentivi per i dottorati di innovazione per le imprese”. The research project carried out during the Ph.D., in collaboration with the industrial partner, Labor s.r.l., and the Sapienza Nanotechnology and Nanoscience (SNN) laboratory of the Research Center for Nanotechnology for Engineering of Sapienza (CNIS), allowed me to perform material formulation and characterization of modified electrospun nanofibers for manufacturing functionalized filtering layer in advanced face masks by means of electrospinning technique. Our findings gave further insight into the implementation of electrospun nanofibers for the realization of the next generation of face masks, with functionalized membranes via the addiction of active material to the polymer solutions that can give optimal features in terms of both submicron particle filtration and antibacterial performance. In particular, from the photocatalytic studies carried out was possible to obtain a further understanding about the photoactivation mechanism of the nanoparticles embedded at the surface of the nanofiber electrospun membrane, promoting an effective deactivation of submicron particle contaminants. Such optimal features of filtration performance, antibacterial, antiviral, and self-sterilization, can help in dealing with the present issues originating from the outbreak of the COVID-19 pandemic and its consequences, given the contamination from bacteria on personal protective equipment surfaces due to the reusability of disposable face masks.