Reusable Molten-nanonet fiber-immobilized air filter with polycaprolactone–polyvinylidene fluoride electrospun nanofibers for enhanced water-wash durability†

Abstract

High-efficiency particulate air (HEPA) filters experience pressure loss and decreased filtration performance over time due to dust layer accumulation; consequently, they need to be frequently replaced. Filter reuse after washing to remove the hydrophilic dust particles collected by the filter deforms the fibers and expands the fiber interstices, resulting in filtration efficiency loss. Even with additional electrostatic treatments, the dust collection capacity of filters cannot be fully restored. This study designs and evaluates a fiber-immobilized (FIM) filter with minimal microfiber migration—a source of structural deformation—and high dust collection efficiency even after multiple washing. First, a nonwoven reinforcement composed of polypropylene (PP) microfiber was subjected to oxygen plasma treatment. Then, a polycaprolactone–polyvinylidene fluoride (PCL–PVDF) complex was co-electrospun on the PP support to create a nanofiber-nanoNet (NN) structure with enhanced electrostatic dust collection capacity. The entire structure underwent heat treatment at 60 °C to selectively melt/sinter the PCL nanofibers. This process formed a molten PCL–PVDF NN (mPCL–PVDF NN) composite, characterized by strong adhesion between the PVDF nanofibers and PP microfibers. The resulting mPCL–PVDF NN-FIM filter demonstrated a filtration efficiency of over 99.7% for particulate matter (PM) ≥0.3 μm, with a pressure drop below 40 Pa. After 20 washing cycles, the FIM filter retained a filtration efficiency exceeding 99.6% (PM ≥0.3 μm) and a pressure drop under 40 Pa. To assess practical reusability, 20 exposure tests were conducted by installing the developed filter in a commercial air purifier which was operated under real indoor dust conditions. Compared to a commercial HEPA filter, the FIM filter was more effective at capturing airborne dust particles because of its high surface area and fine porosity. Therefore, the FIM filter technology can be applied in air purification systems to improve the air quality in buildings and industrial environments.