Abstract
The work aims at the experimental and theoretical study of the mechanism of meltblowing. Meltblowing is a popular method of producing polymer microfibers and nanofibers en masse in the form of nonwovens via aerodynamic blowing of polymer melt jets. However, its physical aspects are still not fully understood. The process involves a complex interplay of the aerodynamics of turbulent gas jets with strong elongational flows of polymer melts, none of them fully uncovered and explained. To evaluate the role of turbulent pulsations (produced by turbulent eddies in the gas jet) in meltblowing, we studied first a model experimental situation where solid flexible sewing threadlines were subjected to parallel high speed gas jet. After that a comprehensive theory of meltblowing is developed, which encompasses the effects of the distributed drag and lift forces, as well as turbulent pulsations acting on polymer jets, which undergo, as a result, severe bending instability leading to strong stretching and thinning. Linearized theory of bending perturbation propagation over threadlines and polymer jets in meltblowing is given and some successful comparisons with the experimental data are demonstrated.
Highlights
In meltblowing the key flow element is a polymeric liquid jet stretched by a high speed gas flow
A realistic description of the dynamics of bending perturbations should account for the interplay of the above-mentioned factors, which determine the pattern of bending perturbation propagation over polymer jets
The experiments in Ref. 19, which established the expression for the aerodynamic drag1͒ used to derive Eq ͑8͒ were conducted with threadlines moving in stagnant air, which does not involve high levels of FIG. 11. ͑Color online The envelope observed in the experiment with a 19 cm long threadline subjected to gas jet issued at 28 bar vs the prediction accounting for only the effect of turbulent pulsations and disregarding distributed aerodynamic lift force
Summary
In meltblowing the key flow element is a polymeric liquid jet stretched by a high speed gas flow. Several important experimental works and references therein demonstrate that polymer jet configurations in meltblowing are extremely transient and nonstraight at already several centimeters from the hole exits in die nosepiece, the jet-jet interactions are significant and merging of neighboring jets is quite possible. Turbulence of the surrounding gas flow can have a very significant effect on the final characteristics of the meltblown nonwovens. It is improbable that polymer jet characteristics in meltblowing are determined by turbulent eddies alone. The interaction with the surrounding gas flow cannot be reduced to only the effect of turbulent eddies, and the interaction with the mean flow can be very significant. A realistic description of the dynamics of bending perturbations should account for the interplay of the above-mentioned factors, which determine the pattern of bending perturbation propagation over polymer jets
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