No abstract

A numerical simulation of melt spinning reveals bifurcation of dynamic solutions leading to limited spinning conditions. The bifurcation phenomenon is controlled by stress-oriented crystallization and crystallinitydependent polymer viscosity. Under the conditions of bifurcation, the space of the spinning conditions (take-up velocity  filament thickness) splits into three regions corresponding to amorphous fibers, partially crystalline fibers, and inaccessible conditions. Major factors affecting the maximum spinning speed and minimum filament thickness for melt-spun poly(ethylene terephthalate) are analyzed.

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 extrapressure 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 subfilaments.