Mechanical properties, fiber orientation, and length distribution of glass fiber-reinforced polypropylene parts: Influence of water-foaming technology

It is generally believed that the length, length distribution, and orientation of fibers are important influencing factors on the mechanical properties of fiber-reinforced polymer matrix composites. In this study, the length, length distribution, and orientation of fibers with respect to the loading direction of glass fiber-reinforced polypropylene (GF-PP) parts were investigated. GF-PP of different initial fiber lengths, 2 mm (SGF-PP) and longer than 2 mm (LGF-PP), were prepared and then molded into parts via conventional injection molding (CIM) and water-foamed injection molding (WFIM). The mechanical performance of samples was determined using tensile and impact tests, the residual fiber length and length distribution were measured, and the fiber orientation was observed by optical camera and scanning electron microscopy (SEM). The experimental results showed that the mechanical properties of LGF-PP WFIM components were better than those of the CIM components, while the SGF-PP parts were worse than the solid ones. The results also suggested that the LGF-PP WFIM samples exhibited the best fiber length and length distribution, and a lesser degree of fiber orientation, along the flow direction, compared with the CIM samples. It was also shown that the fibers in the GF-PP foamed parts that were longer than a critical length, which possibly exceeded that of the solid parts, were more effective in improving the mechanical properties. Thus, it can be concluded that the property enhancements of the LGF-PP parts can be attributed to the effect of cell growth based on an interpretative model of the interaction of long fibers and foamed cells. POLYM. COMPOS., 39:4386–4399, 2018.