Effect of Solvent Exposure on the Filtration Performance of Electrostatically Charged Polypropylene Filter Media

Abstract

Solvent-induced performance deterioration in corona charged polypropylene electret filter media was studied. Electret media, exposed to isopropanol (IPA) in the liquid phase, exhibited reduced filtration efficiency with negligible changes in the pressure drop across the media. Scanning electron microscopy imaging indicated no observable morphological changes after IPA exposure. Solvent-induced efficiency deterioration of electret filter media was hypothesized to originate from charge deterioration rather than charge masking. The charge of the individual fibers in filter media was characterized using electrostatic force microscopy (EFM). EFM investigation produced evidence that exposure to IPA in the liquid phase affected the electrostatic charges on fibers. Exposure to organic solvents such as xylene, toluene, and ethyl benzene has been reported to increase charge mobility in polypropylene fibers, thereby reducing the electrostatic charge and the ability of the fibers in the electret filter media to capture particulates.

Cleanable Air Filter Transferring Moisture and Effectively Capturing PM2.5

“…This behavior could be attributed to the efficient physical interception of the fibrous membrane without loss of the filtration efficiency as observed for electric materials . In contrast, the filtration efficiency value of the commercial melt‐blown fibrous membranes greatly decreased from 99.99% to 87.45% due to gradual deterioration, which could result in potential safety hazards as reported previously . However, we observed an important increase of the pressure drop value for the gradient M1 due to the pores clogged by the PM 2.5 .…”

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“…However, several studies have reported that the degradation of filtration efficiency occurred when PP electret fabrics are exposed to some solvents [4e7]. Kim et al reported no observable morphological change after isopropanol (IPA) exposure via scanning electron microscopy imaging [8]. Their EFM investigation achieved the evidence that exposure to IPA in the liquid phase affected the electrostatic charge of fabrics.…”

Air filters for indoor environments: Interlaboratory evaluation of the new international filter testing standard ISO 16890

“…Xiao et al (2014) correlated their experimental results to the solvent swelling effect and explained it with the Flory‐Huggins solvent swelling theory . However, Kim et al observed no significant morphological change or swelling of the polymer fibers after exposure to liquid IPA . Tang et al (2018) assumed that saturated IPA vapor condensates on the fiber surfaces and calculated the thickness of the liquid IPA layer to a few nanometers via mass difference of the consumed IPA .…”

“…The IPA evaporates until a saturated atmosphere is achieved. To conduct this discharging process, all but one of the participants used the commercially avail- 25 Tang et al (2018) assumed that saturated IPA vapor condensates on the fiber surfaces and calculated the thickness of the liquid IPA layer to a few nanometers via mass difference of the consumed IPA. 21 Besides that, studies showed that unsaturated vapors of organic solvents do not lead to any discharge of the fibrous material.…”