Flow Orientation of Short Fiber Composites

A method for characterizing the orientation of short fibers during flow of short fiber composites is described. A system comprised of approximately 50% by volume glass fibers in an epoxy resin matrix was used for this study. A glass rheometer was used to observe steel tracer fibers, which were incorporated into feed particles with the glass. By reacting the epoxy resin with a secondary amine, a product was obtained which did not react further during the measurements. The product also had a viscosity at room temperature similar to com mercial systems at processing temperatures; this made flow measure ments at room temperature possible. A technique of data reduction for the orientation measurements is described. Early results show that, at these high fiber loadings, plug flow with little change in orientation occurs above and below the constriction in the rheometer tube. At the constriction, particles are sheared into strands. If feed particles containing pre-oriented fibers are not used, a "log jam" results at the entrance to the constriction, preventing flow. The dependence of extrusion pressure on extrusion rate is much less than one finds for unfilled systems.