High-performance and sustainable aerosol filters based on hierarchical and crosslinked nanofoams of cellulose nanofibers

Abstract

Nano-structured and porous foams derived from crosslinked cellulose nanofibers (CNF) were designed and tailored as highly efficient aerosol filters. The lignin-containing CNF was prepared from a recycled milk-container board using deep eutectic solvent pretreatment and mechanical grinding. The nanofoams or aerogels were formed in different densities (initial CNF concentration of 0.2–1.0 wt%) with a freeze-drying process using two silane compounds for strengthening the structure. The filtration performance of nanofoams was studied with a Differential Mobility Particle Sizer (DMPS) setup using 10–500 nm NaCl aerosol particles. DMPS determines particle number size distribution of particles passing through nanofoams which is used to calculate the filtration performance. All nanofoams, which possessed porosity from 99.1% to 99.8% and specific surface area from 5.9 m2 g−1 to 18.6 m2 g−1, achieved good filtration performance (>96%) in the measured particle size range. Very high filtration efficiency (>99.5%) was achieved with the 0.7 wt% nanofoam sample for particles smaller than 360 nm. Based on the quality factors (QF), 0.3 wt% nanofoam produced the lowest pressure drop yet with relatively high filtration efficiency and resulted in the highest QF value that met the N95 standard requirements of respirator face masks. The structure and thickness of the nanofoam filter makes possible high particle bearing without loss on its performance.