Experimental study of long glass fibers breakage in starve-fed single screw extrusion of reinforced polypropylene

An experimental study of fibers breakage in a starve-fed single screw extrusion is presented. A long glass fiber-reinforced polypropylene (LGF-PP) was investigated at various operating conditions, reported in Table 1. The “screw pulling-out” technique was used to study fibers breakage along the screw and its dependence on the melting mechanism. The solid conveying, melting position, the extent of starvation, and the fully filled regions were observed. Polymer samples were stripped off from the screw, which was removed from the machine, to investigate fibers distribution by means of optical microscopy. Contiguous solid melting (CSM) mechanism was observed for flood-fed extrusion of PP filled with 30% LGF (Figure 1a). Dispersive solid melting (DSM) replaced CSM for starve-fed extrusion of PP filled with 40% LGF and blended with neat PP in order to achieve a fiber fraction of 30% (Figure 1a). Fibers breakage was significantly reduced with DSM, as results from the significant improvement of impact strength obtained starve-fed extruding PP filled with 40% LGF and blended with neat PP (Table 1).