Abstract
A N95 face-piece respirator and a 3M air filter composed of non-woven polypropylene filter material were investigated for their multi-scale microstructure and resulting filtration performance. Filtration mechanisms of each system are found and quantified. Both media showed a gradually decrease of the most penetrating particle size with respect to an increase in face velocity or surface charge density. Increasing the face velocity and porosity dramatically degraded the collection efficiency in the 3M filter rather than in the N95 system. We exploited three-dimensional X-ray tomography to characterize the morphological and geometrical properties of the fiber arrangement and deposition of aerosol on the fiber surface. Tuning the most predominant material parameters to achieve a precedence in lower pressure drop or higher collection efficiency in a specifically captured particle size range is of great requisite to a peculiar application of the filter media.
Highlights
Modern technology has improved the quality of life in many aspects, the other side of such a rapid development of industry is severe air pollution, causing serious human health hazards due to the deep penetration of particular matter with fine particle sizes below 2.5 μm (PM2.5) into human lungs [1,2,3]
Air filter media is commonly made from fibrous filters comprising randomly arranged fibers whose distances are larger than the sizes of aerosol particles [4]
Fibrous filters basically capture aerosol particles via four physical mechanisms, including gravity settling, inertia impact, interception, and Brownian diffusion in which each of them plays a crucial role for a particular size range of aerosol particles [4,5]
Summary
Modern technology has improved the quality of life in many aspects, the other side of such a rapid development of industry is severe air pollution, causing serious human health hazards due to the deep penetration of particular matter with fine particle sizes below 2.5 μm (PM2.5) into human lungs [1,2,3]. Fibrous filters basically capture aerosol particles via four physical mechanisms, including gravity settling, inertia impact, interception, and Brownian diffusion in which each of them plays a crucial role for a particular size range of aerosol particles [4,5]. The particle size at the lowest filtration efficiency, named as the most penetrating particle size (MPPS), typically around 0.3 μm or smaller, is used to determine the dominant capture mechanism of the air filter [3,4,6]. Electret filters are dielectric materials-based fibrous filters that possess quasi-permanent static electric charge on the fiber surfaces [7] in which the electrostatic force dramatically enhances filtration efficiency and is responsible for the main capture of fine aerosol particles, resulting in a significant shift towards a smaller particle size of MPPS [8,9,10,11]
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