Experimental study of particle migration in polymer processing

Abstract

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 phenomena 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 screwless extruder that was built in‐house. 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 was observed. In the extrusion and screwless extrusion processes, particles migrated towards the wall, contrary to current theories and believes. 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. 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. Particle redistribution towards the wall and the center during flow could possibly have happened due to migration and fountain flow effects. POLYM. COMPOS., 40:2165–2177, 2019. © 2018 Society of Plastics Engineers