Comparison of thermal conductivities of polypropylene fibers and fibrils

In this work, we compared thermal conductivities of polypropylene fibers and fibrils. The polypropylene fibers were melt spun, and oriented by solid-state drawing. Both wide-angle X-ray scattering and sonic velocity measurements were performed to determine the orientation of fibers. The thermal conductivities of fibers were measured via direct electrical heating method, and that of fibrils were measured via thermal bridge method. Our results show that the thermal conductivity of polypropylene fibers increases linearly with their sonic velocity. This suggests we can use the sonic velocity to characterize the thermal conductivity of semicrystalline polymers. Our results also indicate the average thermal conductivity of fibrils is close to that of fibers. This implies that the low thermal conductivity of polymer fibers is due to the low thermal conductivity of fibrils, instead of thermal resistance between fibrils.