Flow Induced Fiber Orientation in the Molding of Potassium Titanate Fiber/Polystyrene Composites I. Effect of Flow through the Die with Reservoir

The rheological properties of composites filled with 10∼50 wt% of fibers were studied. The flow activation energy was not affected by the addition of fibers. The plots of swell ratio against shear stress were independent of melt temperature. The orientation factors of extrudates and of the samples removed from the capillary after terminating extrusion were examined at various shear rates by WAXD. A skin-core structure was found in the extrudates but not in the sample removed from the capillary. The fibers in the skin were highly oriented along the flow, whereas the fibers in the core were oriented in a zig-zag manner. Goettler's theory for estimating the effect of extensional flow in a reservoir on the distribution of orientation angle could well describe the distributions obtained here. However, the orientation factors estimated from the theory are always smaller than the experimental valves. One possible reason can be ascribed to the neglect of shear effects.