Continuous Drawing of Liquids to Form Fibers

The continuous stretching of viscous liqu ids to form fibers is a primary manufacturing process in the textile industry. The mechanics of certain sheet formation and sheet and wire coating operations are quite similar, as are the mechanics of the formation of glass fibers. Most published experimental and theoretical work has been motivated by applications using polymeric liquids, where the interactions between processing conditions and the complex fluid rheology are of particular interest. The melt spinning process for the manufacture of textile fibers is shown schematically in Figure 1. Molten polymer is extruded through a small hole into cross-flowing ambient air at a temperature below the solidifica­ tion temperature of the polymer. The solidified polymer is taken up at a higher speed than the mean extrusion velocity, resulting in drawing of the filament. The steady-state ratio of extrusion to takeup area is known as the draw ratio (DR); the draw ratio is also equal to the steady-state ratio of takeup to extrusion velocity (to within the approximation that polymer density is independent of temperature). Typical processing variables for the manufacture of poly (ethylene terephthalate) (PET) fiber are shown in Table 1. Commercial PET, a polyester sold under such trade names as Dacron, Terylene, and Fortrel, is a nearly amorphous material as spun, although PET with forty percent crystalline polymer can be produced. Other commercially important melt-spun polymers include Nylon-6, Nylon-66, and polypropylene. The solidified filament is typically subjected