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Seminarium ZTOCNonwovens: Melt- and Solution Blowing - UWAGA: wykład przesunięty na 10 maja, sala S-3 godz 12:00.Alexander Yarin (University of Illinois, Chicago) |
Theoretical and experimental studies on the mechanism of meltblowing - an effective method of producing polymer micro- and nanofibers in the form of nonwoven mats via aerodynamic blowing of polymer melt jets will be presented. The process involves a complex interplay of the aerodynamics of turbulent gas jets with strong elongational flow of polymer melts. To evaluate the role of turbulent pulsations produced by turbulent eddies in the gas jet, we first model the experimental situation where solid flexible sewing threadlines are 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 undergoing severe bending instability leading to strong fiber stretching and thinning. Linearized theory of bending perturbation propagation over threadlines and polymer jets is given, and some successful comparisons with the experimental data are demonstrated. Then, fully nonlinear case of large-amplitude 2D and 3D bending perturbations of a single polymer jet is solved numerically. Multiple jets are modeled simultaneously, as well as deposition on a screen moving normally to the principal jet direction is accounted for. The results include prediction of the fiber deposition patterns and fiber-size distributions in the resulting nonwovens. A novel method - solution blowing is also introduced, where core-shell drops of polymethyl methacrylate (PMMA) and polyacrylonitrile (PAN) are subjected to a high speed gas jet that results in their stretching and bending. As a result of an enormous elongation, after the solvent evaporates, core-shell polymer nanofiber mats are deposited on a screen. Heat treatment allows complete elimination of the core and carbonization of the shell, which yields carbon tubes with an inner diameter 50-150 nm and outer diameter 400-600 nm, and their mats.