Thermal Effects During Hollow Polymer Fiber Drawing

Cylindrical hollow polymer fibers are drawn in an environment in which the heat transfer is approximately half radiative and half convective. A preform is introduced into the drawing furnace through an iris, travels vertically downward through the furnace, and fiber of reduced diameter exits through a bottom iris. For photonic crystal and biomedical applications one or more circular channels are drilled longitudinally in the preform. Challenges arise in the manufacture of hollow polymer fibers because the hole to outer diameter (aspect) ratio of the preform can change as the material is heated and drawn into fiber. Experiments to quantify the trends in aspect ratio changes have been performed. The results indicate that further study of the drawing process for hollow fiber is needed. Experiments with thick walled hollow fibers show poor repeatability even at stable drawing conditions, and the trends were not captured well by existing models. A simple 1-D model is presented and compared to the experimental results.