Effect of high pulling speeds on the morphologies of pultrudates in a thermoplastic pultrusion process

Abstract

During thermoplastic pultrusion, increasing the pulling speed generally leads to a melted polymer pressure rise in the pultrusion dies. Yet, it was not clear if the polymer pressure’s increase would result in a faster impregnation flow that would compensate for the lower residency time inside the heating dies. Thus, the aim of this study was to verify if the speed-induced pressure can counterbalance the decrease in residency time that is required for impregnation quality and to analyze possible pultrudate morphology’s reconfiguration. Three distant pulling speeds were selected: namely 50, 500 and 1000 mm/min. Using a model, the polymer pressure in the pultrusion dies was computed to reach up to 1.0, 10.42, and 20.6 MPa for the respective pultrusion pulling speed. The morphology’s characterization showed a reconfiguration of the pultrudate at a higher pulling speed leading to larger unimpregnated agglomerations and polymer rich areas. The highest tensile strength achieved was 233.4 ± 1.5 MPa at 50 mm/min and dropped by around 20% when the pulling speed was raised to 1000 mm/min. The pultrudate reconfiguration at higher speed, attributed to delayed melting of PP fibers in underfilled dies, is deemed responsible for the loss in impregnation and mechanical properties.