Abstract
The work is devoted to the theory of meltblown polymer jets. Polymer jets are experiencing strong stretching and flapping being subjected to the pulling action of a high speed surrounding axisymmetric gas jet. The bending perturbations of polymer melt jets are triggered by the surrounding turbulent eddies and enhanced by the distributed lift force acting on the jets. We study first growth of small perturbations in the framework of the linear stability theory. Then, the fully nonlinear case of large-amplitude planar bending perturbations of polymer jet is solved numerically. Both isothermal and nonisothermal cases are considered. The cooling of the surrounding gas jet results in cooling of the polymer jet inside, and to the arrest of the bending perturbation growth due to melt solidification.
Highlights
Meltblowing of polymer jets is the main process to form various nonwovens
The approach used in the present work is based on the quasione-dimensional equations of free liquid jets––the technique which had already been successfully applied to the description of bending perturbations of polymer liquid jets moving with high speed in air or in the electric field in electrospinning
The linear and nonlinear theory of meltblowing developed in this work explains the physical mechanisms responsible for jet configurations, and in particular the role of the turbulent pulsations in gas jet, of the aerodynamic lift and drag forces, as well of the longitudinal viscoelastic stress in the polymer jet
Summary
Meltblowing of polymer jets is the main process to form various nonwovens. In this process polymer jets are issued into coaxial high speed gas jets. Accounting for Eq ͑13͒, the latter corresponds to the following dimensionless condition: This means that even though polymeric liquids can develop rather significant longitudinal deviatoric stresses in flow inside the die and carry a significant part of it as xx0 to the “initial” cross-section, the convective effects in the polymeric jet are initially stronger than propagation of the “elastic sound.”. 1–3 for the following values of the parameters: M = 0.001, R = 0.00122, ᐉ = 83000, De= 0.01, and Re = 40, the dimensionless velocity of the gas flow assumed to be constant in the present case is Ug = Ug0͒ = 10, xx0 = 104, H0 = 0.01, and the dimensionless perturbation frequency ⍀ = L / V0 = 1500 These values of the dimensionless groups correspond to plausible values of the physical parameters. After it fades due to the dominant relaxation, a vigorous bending leading to jet elongation and thinning begins
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