Fiber breakage behavior of long glass fiber-reinforced polypropylene through the convergent channel

Fiber breakage occurs during the processing of fiber-reinforced thermoplastics, thereby resulting in the deterioration of the mechanical properties of the thermoplastic parts. In this paper, the fiber breakage and flow behavior of long glass fiber-reinforced polypropylene containing 30 wt% glass fibers was investigated through a series of conical capillary die at varying shear rates, conical die angles or diameters, and the melt flow index of polypropylene. Moreover, scanning electron microscopy was employed to observe individual fiber cross sections to analyze the mechanism of fiber breakage, of which the conical capillary die geometry dominantly affected the residual fiber length, and the choice of an appropriate geometry most significantly affected improvements in the residual fiber length. The results also indicated an increase in the extent of fiber breakage following an increase in the shear rates. In addition, long glass fiber-reinforced polypropylene also generated a slightly higher average fiber length following an increase in the melt-flow index of polypropylene. Pressure oscillations were observed at the entrance, of which these pressure accumulations and releases affected fiber interactions and breakage at the entrance.