Die swell behavior of liquid crystalline mesophase pitch

Die swell of a spinnable mesophase pitch was explored using a fiber spinning apparatus with varied capillary geometries and processing conditions. It was found that the die swell decreased with increased shear rate and increased with a rise of temperature. A nearly constant die swell value can be reached as shear rate gets high enough for different temperatures, and it decreased with increased die angles, but maintained unchanged for capillaries with different length-to-diameter ratios. For orifice die, the die swell ratios were found to be affected little by the extrusion rate and the temperatures. The texture examination of the extrudates from orifice die and dies with capillaries shows that the extensional flow produces high molecular orientation, and the shear flow-induced tumbling might store elastic energy that will be recovered at the die exit.