Abstract
Ambient particulate matter less than 2.5 μm (PM2.5) can substantially degrade the performance of cars by clogging the air intake filters. The application of nanofibers in air filter paper can achieve dramatic improvement of filtration efficiency with low resistance to air flow. Cellulose nanofibers have gained increasing attention because of their biodegradability and renewability. In this work, the cellulose nanofiber was prepared by Lyocell fiber nanofibrillation via a PFI-type refiner, and the influence of applying a cellulose nanofiber on filter paper was investigated. It was found that the cellulose nanofibers obtained under 1.00 N/mm and 40,000 revolutions were mainly macrofibrils of Lyocell fiber with average fiber diameter of 0.8 µm. For the filter papers with a different nanofiber fraction, both the pressure drop and fractional efficiency increased with the higher fraction of nanofibers. The results of the figure of merit demonstrated that for particles larger than 0.05 µm, the figure of merit increased substantially with a 5% nanofiber, but decreased when the nanofiber fraction reached 10% and higher. It was concluded that the optimal fraction of the cellulose nanofiber against PM2.5 was 5%. The results of the figure of merit were related to the inhomogeneous distribution of nanofibers in the fibrous structure. The discrepancy of the theoretical and measured pressure drop showed that a higher nanofiber fraction led to a higher degree of fiber inhomogeneity.
Highlights
Clean air is considered a basic requirement for modern society
Environmental Protection Agency developed the first standard for particulate matter less than 2.5 μm (PM2.5 ) in 1997, as a result of concern over the health effects of fine particles in the air [1]
Cellulose nanofibers were prepared by Lyocell fiber nanofibrillation, and the
Summary
The air quality deterioration and the increasing air pollution has aroused widespread public concerns. The U.S. Environmental Protection Agency developed the first standard for particulate matter less than 2.5 μm (PM2.5 ) in 1997, as a result of concern over the health effects of fine particles in the air [1]. One important effect is that it can substantially degrade the performance of cars, as the combustion engine of a car needs to ingest large quantities of air. As the initial efficiency of the traditional filter paper against fine particles is low, the PM2.5 pollution challenges the filter performance and increases the potential damage for the vehicle engines. As a result of the increasing problems of fine particle pollution, the requirement of better filter performance is more demanding. The global commitment to cleaner energy and less energy usage is Materials 2018, 11, 1313; doi:10.3390/ma11081313 www.mdpi.com/journal/materials
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