Using Swirl Dies To Spin Solid and Hollow Fibers

Abstract

A swirl die was used to produce both solid and hollow fibers from polypropylene. In a swirl die, the molten polymer stream is attenuated and directed (swirled) by a concentric ring of air jets. In our experiments, the ring contained six air jets. The effects of air flow rate, polymer flow rate, air temperature, and polymer temperature were examined. The fiber diameter, swirl pattern diameter, and swirl frequency were measured. To spin hollow fibers, a lumen fluid (nitrogen) was injected into the polymer as the polymer exited the spinning die. The effects of fiber hollowness on the die operation and resulting swirled fiber were determined. A significant finding is that spinning hollow fibers (versus solid fibers) allows production of fibers with larger diameters and higher swirl frequencies. The results of these two improvements are that, for adhesive bonding processes, the bond strength is increased and the line speed can be increased.

A Review on the Studies of Air Flow Field and Fiber Formation Process during Melt Blowing

“…The apparent splaying obtained by naked eye and by low speed photography is an optical illusion formed by a very fast whipping motion of the fiber. A similar image of a melt blown fiber under a swirl die (Figure c) was photographed by Marla et al…”

“…The apparent splaying obtained by naked eye and by low speed photography is an optical illusion formed by a very fast whipping motion of the fiber. A similar image of a melt blown fiber under a swirl die (Figure 5c) was photographed by Marla et al 19 Although the photography technique has been adopted to investigate the melt blown fiber motion for several years, the trajectory of a single fiber has never been captured until Beard et al 67 used a high speed camera to record the motion of fibers below a melt blowing slot die (Figure 5d) and a swirl die (Figure 5e), respectively. Xie and co-workers 64,68 employed a high speed camera working at 5000 frames/s to capture the fiber trajectories.…”

“…An annular die is the type with each polymer orifice surrounded by an annular air outlet. Apart from the slot and the annular dies, there are some other die designs reported in literatures such as the swirl die (Figure e, f) , and the parallel plate die . Researches on die designs are divided into two categories.…”

“…Copyright 1993 American Chemical Society. (e, f) Reprinted with permission from ref . Copyright 2006 American Chemical Society.…”

Experimental Investigation of the Fiber Formation Process and Web Structures Using an Annular Meltblowing Spinneret

“…In this setup, molten polymer is pushed through a single row of capillary outlets and attenuated into fibers by converging air curtains. This design has been studied experimentally and theoretically − and has been modified to create supersonic air streams and multicomponent fibers. − Departures from the standard linear die have also been patented and commercialized, but not as thoroughly studied. − …”