Study of the effect of process parameters on fiber length, fiber orientation and tensile strength of long glass fiber reinforced polypropylene molding

In this study, investigation of the effect of process parameters on fiber length, fiber orientation and tensile strength of long glass fiber reinforced polypropylene molding. In the study, the polypropylene composite material with glass fiber length of 25 mm was taken as the research object. The special long fiber injection molding machine was used to investigate the change of fiber quality, and the injection molding experiment was carried out with different screw speed and back pressure, and observation on the fracture condition of the fiber during the plasticization process, using this as the basis for the process parameters setting. A tensile test specimen mold with different melt flow path was designed to understand the effects of process parameters on tensile strength properties of long fiber injection molding. It can be found from the experimental results that in the fiber breaking length experiment using the three-stage with plunger mechanism of the special injection molding machine for long fiber reinforced thermoplastic composite molding, increasing the screw speed and the back pressure will shorten and break the fiber (retain 40~50% of the fiber length). The length of the fiber further affects the tensile strength of the molded specimen. On the other hand, as the melt temperature and mold temperature increase, it affects the fluidity and compatibility between melt and glass fiber, the tensile strength will have a relatively increased trend. From the microstructure observation showed that the tensile specimen closer to the gate has poor fiber diffusibility and affects the tensile strength of the molded specimen; moreover, the tensile specimen with double gate melt flow path resulted lower weldline strength.