The role of mandrel rotation speed on morphology and mechanical properties of polyethylene pipes produced by rotational shear

Properties of plastic products depend on their microstructure and morphology. To improve the pressure rating (maximum pressure) of plastic pipes, a novel rotational shear system (RSS) was developed in this study to fabricate plastic pipes with enhanced hoop tensile strength through applying hoop shear on the pipes using a rotational mandrel. Morphology study results showed that different morphologies of the HDPE pipes were produced when the mandrel rotated at 5 rpm, 7.5 rpm, 10 rpm, 12.5 rpm and 15 rpm. The hoop tensile strength and heat resistance of the pipes were found to increase rapidly with the rotation speed and the properties peaked at 7.5 rpm. At this speed, the hoop tensile strength and Vicat softening temperature (VST) increased by about 338% and 26.8 °C, respectively. The axial tensile strength of the pipe was also slightly improved under this condition. The high mechanical and thermal performance of the pipe produced at 7.5 rpm was attributed to homogeneously distributed shish-kebab structures throughout the pipe wall.