Effect of Mixing Pressure in Injection Molding on Interfacial Shear Stress of GF/PP Short-Fiber Reinforced Plastics

摘要

In polypropylene resin matrix glass fiber injectionmolding composite materials, surface of fibers is usually treated bycoupling and/or sizing agent and resin is modified by maleic acidbecause mean fiber length is shorter than their critical length, andinterfacial adhesion strength between fibers and resin is low.Therefore, fiber strength has not been utilized completely in thesecomposite materials. In the present study, we propose a method toimprove the interfacial adhesion strength by increasing shear strengthbetween fibers and resin, which can be attained by increasing mixingpressure in kneading machine. Since stress-strain relation ofcomposite materials is affected by surface treatment of fibers,interfacial adhesion strength was evaluated by the average interfaceshear stress through a visco-elastic model. The effect of mixingpressure was discussed based on the shear stress. For a compositemaaterial with no surface treatment of fibers and no resinmodification, the interfacial shear strength was higher for highermixing pressure. On the other hand, for a composite material with thesurface treatment and the modification, the effect of mixing pressureon the shear strength was not observed. For these materials, however,higher mixing pressure also contributes the adhesion strengthbetween fibers and resin because fiber length in the materials islonger for higher mixing pressure.