Relationship between extrusion condition and mechanical properties of FRPP

In this work, the relationship between extrusion condition and mechanical properties of glass-fiber-reinforced polypropylene (FRPP) was investigated. It was found that the extrusion flow rate was higher but the extrusion pressure was lower as the fiber content decreased. The flow rate and pressure were more temperature-sensitive at high screw speed. As for the mechanical strength of FRPP, the yield strength decreased with increasing the fiber content, but modulus and impact strength significantly increased with increasing the fiber content. The high screw speed did not affect the mechanical strength of PP, but decreased the strength of FRPP. At higher extrusion temperature, the yield strength and modulus of FRPP increased, but the impact strength decreased. The yield strength and modulus of extrudates along the longitudinal direction of extruder were always higher than those along other directions by the effect of fiber orientation. The specimens taken from different positions of extrudate would show different mechanical strength. The way of cooling for the extrudates would affect the mechanical properties of FRPP, too. All the above relations were discussed and well explained from the contribution of fiber distribution, fiber length, crystallinity of PP, and void content.