Polypropylene hollow fibers were prepared via melt spinning at speeds of 1000–2500 m/min. The outside diameters of the fibers were measured on‐line with high‐speed photography. The fiber formation process was modeled with momentum, energy, and two continuity equations (one for the polymer, and one for the lumen fluid). The equations were solved numerically, and the results were compared to the on‐line diameter data. Both Newtonian and viscoelastic constitutive equations were considered.

Isotactic polypropylene hollow fibers were produced by melt spinning. Spinning speeds up to 1880 m/min were used, and sample hollowness (percentage void in cross section) ranged from 0 to 69%. The fiber samples were characterized using dynamic mechanical analysis, birefringence, tensile testing, and differential scanning calorimetry. The hollow fibers were found to have higher crystallinity, orientation, and strength than the analogous solid fibers. In general, the polymer orientation in a hollow fiber was larger than the orientation in a solid fiber, even when the spinning speed for the latter was much larger. For a fixed outer diameter, increasing the hollowness improved fiber properties. However, as hollowness was further increased, fiber properties declined slightly. At a given percentage hollowness, increased spinning speed increased modulus and tenacity.

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