History and Future of Nanofibers in Filtration

Jon Rajala, PhD, explains the history and future of nanofibers in filtration in this recorded conference session at the 2023 NAFA Technical Seminar in Atlanta, Georgia. Learn about the historical development of nanofiber technology dating back to the 1600s. Gain insights into the current challenges faced in nanofiber filter development. Explore the future of nanofibers as Rajala illuminates key developments that will bring nanofiber filtration to the forefront of the industry. View Dr. Rajala’s slides here: https://amped.egnyte.com/dl/BwSTz9Fb4c For detailed show notes, read below and use the timestamps to navigate the episode: [2:04] Dr. Rajala explains what nanofibers are and how their unique properties make them useful. He defines a nanofiber as one thousand times smaller than a piece of hair, as their distinction comes from their size. [3:09] Dr. Rajala explains the early history of nanofibers. The science of electrospinning dates back to the 1600s when scientists observed how liquids behaved in electric fields and conceptualized the Taylor Cone. In the 1800s, English physicist Lord Raleigh observed that the Taylor Cone shape ejected droplets outwards. Years later, researchers used these findings to learn that polymer chains could be drawn out and pulled into one nanofiber. [5:38]: Dr. Rajala defines and explains electrospinning, which is the main method of producing nanofibers in the filtration industry. The process involves applying a high voltage to a polymer solution. The fibers are then jetted, whipped, and drawn down to the grounded collector. [6:38] Dr. Rajala details how the unique properties of nanofibers come from their nano-dimension structures. Because nanofibers have a high surface area to volume ratio, they can produce significant effects without contributing much weight. This makes them highly useful and functional. [7:43] Dr. Rajala and his team researched at ways of producing catalytic converters with nanofibers to remove harmful gasses from the exhaust of lawnmower engines. [9:14] Dr. Rajala touches on the physics of air filtration. The important property for nanofiber filtration is airflow. The velocity is roughly zero at the surface of a regular fiber, but nanofibers are smaller and do not have a zero velocity gradient at that point. This allows for better airflow. [10:25] Dr. Rajala discusses the current state of nanofibers. The PTFE HEPA filter media is a nanofiber application that shows how bigger fibers perform versus smaller fibers. [13:27] Dr. Rajala compares microglass to synthetic nanofiber media. They have comparable initial resistance and dust-holding properties. [16:03] Dr. Rajala explains the performance difficulties in the current state of nanofiber media. He points to electrostatic charge and dust capacity as the main challenges to overcome. For example, a MERV15 filter with an electrostatic charge will degrade in performance over time. [20:02] Another challenge with nanofibers is inconsistency. A fine layer of nanofibers can be easily damaged. More rigid structures are more successful than depositing and coating nanofibers on existing media. [21:30] Dr. Rajala delves into the future of nanofibers in filtration. Testing filters with ASHRAE disadvantages nanofiber filters due to their unique properties. The test dust includes more large particles than the filter would naturally encounter, making it less favorable to nanofiber filter performance. Better ways of testing filters with more realistic particle size distribution could show how nanofibers realistically perform and give them more traction in the industry. [25:03] Dr. Rajala projects that people will improve lower-efficiency media with nanofibers. Nanofiber media will maintain efficiency throughout its life, increasing its appeal to the industry. As more people are drawn to nanofiber medias, people will develop better ways to implement nanofiber medias.