Hollowness Variation with Die Wall Thickness in Melt-Spinning of Polypropylene Hollow Fibers

A hollow fiber poses great potential as it can provide superior performance at low weight and low cost. Its unique properties come from its geometry, the presence of void and air inclusion, but controlling it is a challenging problem. This study explores how the geometry of a die influences fiber hollowness. Fibers were extruded from dies with four segmented arcs, 4-C, which had varying die wall thickness and constant inner diameter. The effects of die wall thickness on wall-shear rate, solidification, spinnability, and hollow fiber geometry are evaluated under various processing conditions. Both processing parameters and die wall thickness influence hollow fiber dimensions and hollowness, but die wall thickness has the largest impact. Reduction of die wall thickness decreases fiber wall thickness, increases the outer and inner diameter, and increases hollowness. It can be explained by higher die hollowness and faster extrudate solidification. However, the thinnest die shows reduced spinnability.