Surface Energy of Filtration Media Influencing the Filtration Performance against Solid Particles, Oily Aerosol, and Bacterial Aerosol

Abstract

Particulate airborne pollutants are a big concern to public health, and it brings growing attention about effective filtration devices. Especially, particulate matters smaller than 2.5 µm can reach the thoracic region and the blood stream, and the associated health risk can be exacerbated when pathogenic microbials are present in the air. This study aims at understanding the surface characteristics of nonwoven media that influence filtration performance against solid particles (sodium chloride, NaCl), oily aerosol (dioctyl phthalate, DOP), and Staphylococcus aureus (S. aureus) bacteria. Nonwoven media of polystyrene (PS) fibers were fabricated by electrospinning and its pristine surface energy (38.5 mN/m) was modified to decrease (12.3 mN/m) by the plasma enhanced chemical vapor deposition (PECVD) of octafluorocyclobutane (C4F8) or to increase (68.5 mN/m) by the oxygen (O2) plasma treatment. For NaCl particles and S. aureus aerosol, PS electrospun web showed higher quality factor than polypropylene (PP) meltblown electret that is readily available for commercial products. The O2 plasma treatment of PS media significantly deteriorated the filtration efficiency, presumably due to the quick dissipation of static charges by the O2 plasma treatment. The C4F8 treated, fluorinated PS media resisted quick wetting of DOP, and its filtration efficiency for DOP and S. aureus remained similar while its efficiency for NaCl decreased. The findings of this study will impact on determining relevant surface treatments for effective particulate filtration. As this study examined the instantaneous performance within 1–2 min of particulate exposure, and the further study with the extended exposure is suggested.

Material Properties Influencing the Charge Decay of Electret Filters and their Impact on Filtration Performance

“…Commonly available commercial electret filter media is made by corona-charging. Rather recently, electrospun webs have been regarded as potential electret filter material, while its scalability is yet challenging [8][9][10][11][12]. In most cases, both hetero-and homo-charges exist simultaneously, and the dominant type of charges determine the character of the electret [3].…”

Advanced Design of Fiber-Based Particulate Filters: Materials, Morphology, and Construction of Fibrous Assembly

“…Between the solid and oily aerosol, oily aerosol makes the filter efficiency deteriorate more rapidly in general, because the oily liquid easily spreads on the fiber surface, quickly masking the charged sites [ 24 , 25 ]. The air flow influences the air resistance or pressure drop of the test sample.…”

“…In general, the filtration performance of electret filters decreases more rapidly against the oily aerosol than the solid aerosol, because the immediate spreading of oily liquid on the fiber surface masks the surface charges of the filters [ 25 , 29 , 30 ]. To prevent the rapid masking of charges, the surface of electret filters was modified for oil resistance, and the effect of hydro/oleophobic treatment on filtration efficiency was investigated [ 24 , 30 , 33 , 55 , 74 ]. The surface energy of filter media was lowered by fluorination of the surfaces [ 24 , 30 , 33 , 55 , 74 ], and the resulting web showed superhydrophobicity or superoleophobicity.…”

“…To prevent the rapid masking of charges, the surface of electret filters was modified for oil resistance, and the effect of hydro/oleophobic treatment on filtration efficiency was investigated [ 24 , 30 , 33 , 55 , 74 ]. The surface energy of filter media was lowered by fluorination of the surfaces [ 24 , 30 , 33 , 55 , 74 ], and the resulting web showed superhydrophobicity or superoleophobicity. When the immediate wetting by the oily aerosol was deterred, the collection efficiency against dioctyl phthalate (DOP) was maintained longer with the continued loading of aerosol [ 30 ], while the instantaneous efficiency was not significantly different [ 24 ]; with a submicron layer of coating, the resistance was not affected.…”

Water-Resistant Mechanoluminescent Electrospun Fabrics with Protected Sensitivity in Wet Condition via Plasma-Enhanced Chemical Vapor Deposition Process

“…To attach the oxygen group to the composite surface, the composite fabric was subject to an O 2 plasma treatment for 5 min at 200 W with 160 cm 3 /min in the plasma system (COVANCE, FemtoScience, Hwaseong, South Korea) [41]. To coat the surface with the fluorinated compound by the plasma-enhanced chemical vapor deposition (PECVD), the composite fabric was treated under C 4 F 8 gas for 25 min at 200 W with 100 cm 3 /min [42,43]. The generated frequency of plasma was 50 kHz in both O 2 and C 4 F 8 plasma processes.…”