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Abstract:
The dynamics of stationary air drawing in the melt blowing of nonwovens were determined on the basis of a single-filament model in a thin-filament approximation that accounts for polymer viscoelasticity, heat of viscous friction in the polymer bulk, and surface energy. Predetermined distributions of the air velocity and temperature along the melt blowing axis were assumed. Axial profiles of the polymer velocity, temperature, elongation rate, filament diameter, tensile stress, and extra-pressure were computed for the melt blowing of isotactic polypropylene. The effects of the air-jet velocity, die-to-collector distance, and polymer molecular weight are discussed. We predicted that the filament attenuation and velocity at the collector located in the air-drawing zone would increase with increasing die-to-collector distance. The air-drawing zone was shorter for higher air velocities and lower molecular weights. No online crystallization was predicted before the achievement of the collector, and melt bonding of the filament in the web should have occurred during cooling on the collector, accompanied by spherulitic crystallization. Significant online extrapressure in the filament was predicted in the case of supersonic air jets as resulting from polymer viscoelasticity, which could have led to longitudinal splitting of the polymer into sub-filaments.

Keywords:
fibers, polymer melt, modeling of melt spinning, polypropylene

Abstract:
Computer simulation of the pneumatic melt spinning of isotactic polypropylene based on the mathematical model of the process is presented. Two dynamic zones of the air jet-filament interactions along the melt blowing axis are predicted – a zone with a drawing activity of the air jets with aligned filaments in this zone, and a passive zone with the bending and coiling of the filaments. The diameter of the fibres and structure of the nonwoven should depend on the die-to-collector distance, and the zone in which the collector is located. Ranges of the zones are discussed as dependent on the initial velocity of the air jets, the melt extrusion temperature, and the molecular weight of the polymer. Axial profiles of the polymer velocity, diameter and temperature of the filament, the tensile force, tensile stress, and rheological pressure along the melt blowing axis are presented for a process with the collector located within the air-drawing zone at a fixed take-up distance. The dynamic profiles indicate a narrow axial range of air-drawing next to the spinneret.

Keywords:
melt blowing, air-drawing, nonwovens, polypropylene, modelling

Abstract:
Melt-blowing is an industrial method for rapid production of nonwovens. In melt-blowing, a polymer melt is extruded through capillary dies while hot air is blown through a longitudinal air nozzle. The air drag forces subjected on the polymer streams cause fast attenuation of the polymer filaments into fine diameter fibres at the take-up. A modified mathematical model of melt spinning for a pneumatic process is presented which accounts for the effects of structural transformation under viscoelastic behavior of the polymer. The model is applied to a novel method of nonwoven formation under supersonic air jet.

Keywords:
mathematical modeling, pneumatic melt spinning, supersonic air jet, nonwoven formation