THE RHEOLOGY, FIBER ORIENTATION, AND PROCESSING BEHAVIOR OF FIBER-FILLED FLUIDS

Experimental measurements of the rheology, morphology, and flow characteristics of polymer melts containing suspended glass fibers were interpreted by employing the Doi-Doraiswamy equations for rigid rod (liquid crystalline) suspensions. The fibers were found to be generally aligned along the streamlines of the flow even at very low deformation rates. The diagonal elements of the second-order orientation parameter tensor, which describe the perfection of the orientation, were generally predicted well by the theory using parameters obtained from rheological measurements only. Extraordinary surface irregularities were observed for suspensions extruded from circular dies, and a number of factors were examined in detail to formulate a mechanism for this flow behavior. The two most important factors affecting extrudate morphology appear to be the flexing of fibers at the surface of the extrudate and rotation of fibers in the rearranging velocity profile at the die exit.