(609f) Fabricating a ‘Breathable’ Porous Flat Sheet Membrane Via Non Solvent Induced Phase Separation (NIPS) for Face Masks and Other Air Filtration Applications

The ongoing Covid 19 pandemic has led to growing demands for face masks around the world for protection against the infectious Sars-Cov-2 virus. 3M, a Personal Protective Equipment (PPE) manufacturing company, reported a global production of two billion respirators in 2020. The most common material used in producing these commercially available face masks and respirators is polypropylene (a non-biodegradable thermoplastic) because of its chemical resistance, lightweight, and low cost. A study in six countries across Asia, Europe, and North America showed that individuals between ages 16 and 65 consume about five (5) face masks per week, resulting in an estimated range of 3 to 928 million face mask waste per week in all countries studied. This could result in a polypropylene weekly waste ranging from 8 tons in lower populated countries to 2450 tons in denser populated countries. To reduce the waste caused by the excessive but essential use of face masks, studies have proposed implementing various decontamination techniques such as chemicals, detergents, heat, microwave, and ultraviolet light to ensure the safe reuse of facemasks. These techniques have been reported to reduce the mask filtration efficiency (FE) and compromise the mechanical properties of the mask material. This work involves the fabrication of a breathable high FE porous flat sheet polysulfone membrane resistant to common decontamination processes for face mask manufacture, which could potentially address the limitations of reusing nonwoven facemasks. The breathable membranes were fabricated by nonsolvent induced phase separation (NIPS) using casting solutions containing polyethylene glycol (PEG) as an additive to improve airflow and reduce pressure drop across the membrane. Fourier transform infrared (FTIR), x-ray photoelectron spectroscopy (XPS), and differential scanning calorimetry(DSC) analysis confirmed the absence of PEG in the fabricated membrane, indicating additive dissolution in the nonsolvent during phase separation. Scanning electron microscope (SEM) images of the fabricated membranes showed a large fingerlike pore structure, suggesting fast solvent exchange reported to result in membranes with increased flux. Air permeation and pressure drop tests conducted across the samples showed lower resistance to airflow and pressure drop across membranes made from solutions containing additives. Membranes made from casting solutions with PEG molecular weight of 1000, 4000, 8000, and 10000 daltons at a polymer-additive-solvent concentration of (15/10/75)%w/w resulted in airflow rates of 4.61±0.06, 5.14±0.01, 13.28±0.08, 20.85±0.98 liters per minute (LPM) respectively, which suggests an increase in pore size with PEG molecular weight. The FE of the highest airflow membrane was observed to be 99.5% for particles greater than 300µm after testing using aerosolized NaCl particles at 35LPM. The breathable membrane, N95, and surgical masks were washed with detergent for 1 hour and dried to estimate the effect of a common and simple decontamination process. We observed an insignificant effect of washing with detergent on the fabricated membrane sample FE; however, there was a 20-25% reduction in N95 and surgical mask FE. The decrease in FE was due to depleted surface charges responsible for high FE in electret filter media, which functions by electrostatic interaction mechanism.