Characterization of factors that affect charge decay in fibrous electret

Fibrous media are frequently used for air filters due to their high filtration efficiency and low-pressure drop. However, most particles of air-born dust are less than one micrometer in size, and they are difficult to remove from the air stream by fibrous media like meltblown (MB) nonwoven. It is known that the filtration efficiency of fibrous media can be greatly improved by electrostatically charging the fibrous media because its filtration efficiency is governed not only by mechanical mechanisms but also by electrostatic mechanisms. Hence, the main feature of electret filters is their ability to effectively remove fine particles from polluted air by strong electrostatic forces generated by the electret fibers while offering less resistance to the airflow. This kind of electrostatic force is governed by the charges in the filter media. In general, the charge will decay naturallyIts retention life relies on the charging techniques, the material properties and environmental effectsHence, the major concern of electret media is maintaining the charge on the material.

In this research, charge decay was evaluated in terms of filtration efficiencySeveral basic parameters affecting the charge decay were studied to characterize the electric charge decay on the media. A long-term test for natural decay and a short-term test for thermal decay were run and compared to determine how the factors affect charge decayA charge transfer was proposed to explain charge decay. This states charges inside the fibers will migrate and relocate or dissipate themselves by thermal agitation to a new thermal equilibrium. Then, a method such as Thermally Stimulated Current Discharge (TSCD) was used to determine the energy level of charges stored on media by heat treatment to accelerate the charge decay rate of filter media. Finally, by combining the experimental results above, a special method derived from the Arrhenius Law and the Debye equation was proposed to predict the long-term charge on the electret media.