Using Swirl Dies To Spin Solid and Hollow Fibers

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.