The Structure and Performance of Short Glass Fiber/High-Density Polyethylene/Polypropylene Composite Pipes Extruded Using a Shearing–Drawing Compound Stress Field

Glass fiber reinforced polyolefin composite materials have many advantages regarding their performance and have been widely used in many fields. However, there are few reports on the simultaneously bidirectional self-enhancement of glass fiber reinforced polyethylene/polypropylene composite pipe. To self-reinforce the pipe’s circular and axial properties simultaneously, short glass fiber reinforced high-density polyethylene/polypropylene (SGF/HDPE/PP) pipes were extruded using a shearing–drawing two-dimensional compound stress field pipe-extrusion device. The effects of the rotating speed of the rotating shear sleeve on the orientation, heat behavior, microstructure, and tensile strength of the pipe were investigated in this paper. The microstructure was observed using scanning electron microscopy (SEM), and the crystal diffraction was analyzed using a polycrystalline X-ray diffractometer (WAXD), the heat behavior was measured using a differential scanning calorimeter (DSC), and the tensile strength was tested using a universal electronic tensile testing machine. The results showed that the shear induction effect induced by the shear rotating promoted the formation of the oriented structure of the crystal plate and SGFs along the circular and axial directions of the pipe simultaneously. Furthermore, it increased the crystallinity of the system, and self-improved the pipe’s circular and axial tensile strength at the same time.