The polymer melt swelling behavior in micro-extrusion process for preparation of continuous carbon fiber reinforced PP prepreg filament

Abstract

The micro-extrusion process for polymer melt has been increasingly used for the production of high value-added prepreg filaments with applications in the fields of fused deposition modeling (FDM). In this study, the effect of characteristic scale, defined as the gap of die land in an annular micro-extrusion die, on the extrudate swelling behaviour of viscoelastic melt is analyzed through numerical simulations and micro-extrusion experiments. The results show that the swelling behaviour displays an obvious dependence on the characteristic scale. An increase in the characteristic scale reduces the swell ratio and retards the process to reach the equilibrium state. In contrast, a decrease in the characteristic scale results in a larger magnitude of change in velocity field and faster relaxation development of stress field. The location of the maximum velocity layer for the laminar flow gradually deviates from the geometric center of channel toward the wall of mandrel with the increase in the characteristic scale. It is imperative to consider the complicated swelling behavior and remarkable viscoelastic effect simultaneously in micro-extrusion process.