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(Nanowerk News) The Department of Mechanical Engineering of the Polytechnic University of Hong Kong (PolyU) recently developed a multi-layer electrostatic charge nanofiber filter capable of capturing pollutant particles with a diameter of less than 100 nm (covering most nanoparticles suspended in the air). Particles and viruses). The new nanofiber filter has better performance in terms of breathability, filtration efficiency (10% more than the conventional electret microfibre filter) and durability (up to 90 days).
Nano-aerosols with a diameter of less than or equal to 100 nm exist everywhere in urban areas and, because of their small size, can be easily inhaled into the human body. Most viruses suspended in the air, from influenza to epidemic viruses such as swine flu or SARS, also have a size up to 100 nm. Scientists are still struggling to develop an easy-to-use air filter or mask to effectively capture nanoparticles and protect people from harmful air contaminants and viruses that can be harmful to health.
The team led by Ir. Prof. Wallace Leung Woon-Fong, chairman of the board, professor of technologies and innovative products, used and tested polyvinylidene fluoride (PVDF), a semi-crystalline thermoplastic commonly used as insulation on electrical wires, for the manufacture of nanofiber filters. Applying innovative technology in Corona Discharge, the team has imparted electrostatic charges to the PVDF nanofiber to induce electrical interaction with aerosols at a close distance and effectively capture aerosols.
Compared with other filters manufactured on the market with filled microfibers or unfilled fibers, PolyU's innovative filters have a much improved filtration efficiency, without increasing pressure drop over time (more pressure loss). high means that the filter has greater resistance to airflow and is therefore less breathable user mask or reduced flow for a space filter). The PVDF nanofiber has been shown to be stably charged, with its charging effect remaining for nearly three months. In previous work on the charge of other nanofibers, the transmitted charges usually dissipate in a day.
PVDF Nanofiber Filter Loaded
During the PolyU team's aerosol filtration tests of various sizes, the loaded PVDF nanofiber filter showed a pressure drop of only 5 Pa (Pascal / pressure unit) and a filtration efficiency of order of 54% for the 100 nm particle (ie airflow through the filter, 54% of the 100 nm diameter nanoparticles being trapped), compared to 17% of a 100 nm filter. nanofibers of PVDF not loaded.
The "quality factor" was also multiplied by 2.7: the ratio between the efficiency of the filtration and the pressure drop, or the benefit / cost ratio. The higher the quality factor, the better the performance of the filter, taking into account the importance of filtration and breathability.
Professor Leung said that since viruses generally carry negative electrostatic charges, they can be captured very efficiently by positively charged PVDF nanofibers. "The filter or facial mask applying our innovation would therefore be an ideal defense against viruses in the event of an epidemic."
New layers of electrostatic separator
To further enhance the electrostatic capture performance of the filter, the research team has developed the configuration of several layers of electrostatic separator – distributing the same weight of PVDF nanofibers in a single layer filter in multiple filter layers, each layer being isolated by a separator, to reduce electrostatic interference between fibers of adjacent layers and increase the efficiency of the filter by electrostatic force.
Filtration tests showed that the filtration efficiency of the filters with several charged electrostatic separator layers (two-, three- and four-layer tests) was 39% to 45% higher than the filter without separator. The quality factor of the filters with several charged electrostatic separator layers was 2 to 3.5 times higher than that without a separator.
Stability and durability
Charge on the filter media and its badociated electrostatic effect will dissipate over time. The filter durability test proved that PolyU's new electrostatically charged nanofiber filter with multiple separating layers could sustain high performance over a long period of time. It is therefore more durable and can be stored longer.
Filtration efficiency tests in a humid moist atmosphere with a relative humidity of 80% (the annual average moisture percentage of Hong Kong is 77.0%) for four-layer filters of electrostatic separator (with 1.75 gram of fiber per square meter) showed that the filtration efficiency did not drop days and only decreased by 1% after 90 days.
Potential applications
PolyU's innovation can be widely applied to air filtration, from industrial applications to personal and home applications. Industrial use includes dust-free rooms and fossil fuel plants. Air filtration can also be used to reduce particulate emissions from the exhaust gases of ships and vehicles. The personal and domestic use of air filtration includes face masks, air purifiers, vacuum cleaners, window filters, and so on.
The electret PVDF nanofiber filter can be used in Western Blot, an badytical technique widely used to detect or extract proteins. In the process, the PVDF membrane is often used to transfer proteins separated from the original sample. PolyU innovation can help dramatically improve the electrostatic strength of the nanofiber carpet in protein capture, while maintaining the integrity of the protein without compromising its organization.
Innovation can also be applied to the effective release of protein-based drugs. Drugs manufactured in powder form, for example asthma medications, can be electrostatically captured by the loaded PVDF nanofiber mat for more efficient release and inhalation by users. In addition to drugs administered by inhalation, innovation can also be applied in the same way to drugs to be used topically on the skin.
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