Effect of Cross-Sectional Configuration on Fiber Formation Behavior in the Vicinity of Spinning Nozzle in Bicomponent Melt Spinning Process

To investigate the fundamental melt spinning behavior of the islands-in-the-sea (S/I) fibers,bicomponent melt spinning of polystyrene (PS) and polypropylene (PP) with the composition of 1 : 1 was performed using a spinning pack for preparation of S/I fibers with 1519 islands in the fiber cross-section. The sheath-core (S/C) fibers and blend fibers of the same composition were also prepared for comparison. The reduction ratio of the cross-sectional area of polymer flow from the position of the confluence of two polymer flows to the die exit for the sheath-core type spinning pack is 16 : 1, whereas that for the islands-in-the-sea type spinning pack is 3200 : 1. In this research, particular attention was paid to the behavior of polymer flow in the vicinity of spinneret. Magnitude of die-swell decreased with the increase of extrusion temperature. It was also found that the swelling was more significant for the S/I spin-line in comparison with that for the S/C spin-line. When the S/C and S/I components were exchanged from PS/PP to PP/PS, the swelling behavior of S/C spinline decreased whereas that of S/I spin-line did not show any significant change. On the other hand, magnitude of die-swell for the blend spinning was larger than that for the S/I and S/C spinnings and increased with the increase of extrusion temperature. The distance from the spinneret surface to the position of maximum spinline diameter increased in the order of S/C<S/I<blend. These results suggested that the swelling effect in the S/C and S/I spinning is governed by the viscoelastic effect whereas that in the blend spinning is caused mainly by the interfacial tension between the two components.