Can Supersonic Melt Blowing Produce Stable Nanofibers?

Melt blowing is a process in which a molten polymer is extruded through a line of holes (d~0.2 mm) and stretched between two jets of hot air to produce microfibers (d_avg ~1-5 micron). Nanofibers (d_avg <1 micron) are desirable due to their high surface area per volume. One method to produce nanofibers is to increase the stretching force by increasing air jet velocity but this undesirably increases the amount of broken and uncollected fibers (a.k.a. flies). Numerical simulation shows that steadily increasing air jet velocity results in supersonic air flow and the appearance of compression waves (rapid oscillation in air velocities). This is corroborated experimentally with Schlieren visualization. Increase in flies generation at higher air jet velocity is probably related to the appearance of the compression waves. Laval nozzle (a converging-diverging nozzle) concept is applied to alleviate the compression waves and its influence on melt blowing is investigated.