Extrusion and injection molding processes of filled polymers are widely used in industry due to their high strength-to-weight ratios and for their ability to manufacture a variety of geometries while improving the overall mechanical and thermal properties. However, filler migration and filler-matrix separation during processing are phenomenon that are not fully understood. To gain an improved understanding of these phenomena, polypropylene samples with different glass bead concentrations were manufactured using extrusion, injection molding, and a customized screw-less extruder. Computed tomography was performed on the samples to observe particle position and distribution after material solidification.
For all three-processes, filler migration and filler-matrix separation were observed. In the extrusion and screw-less extrusion processes, particles migrated towards the wall, contrary to current theories. During the injection molding process, filler-matrix separation was manifested as bead-free zones in the center region and the walls of the spiral mold at the entrance region of the spiral mold as shown in Figure 1. These bead-free zones were later filled at the far end of the spiral mold, suggesting migration of particles along flow, with almost no bead-free zones at the end of the mold suggesting particle redistribution toward the wall and the center during flow – possibly due to migration and fountain flow effects.
Particle-matrix separation during mold filling at the entrance of the mold
Particle-matrix separation during mold filling at the end of the mold