The effect of high-temperature annealing on thermal properties and morphology of polyethylene pipes prepared by rotational shear

To improve the thermal properties and maximum pressure of plastic pipes, a self-developed rotational shear system (RSS) was prepared in this study to form the plastic pipes containing high oriented shish-kebab through imposing rotational shear field. When the rotational shear was performed at 8 rpm, the hoop tensile strength, thermal conductivity in in-plane and heat resistance of the pipes increased by 235.9%, 34.4% and 32.6%, respectively. With the annealed temperature close to 125 °C for 40 min on the pipes, thin-lamella could be melted to the amorphous phase that facilitated the random chains rearrange on thick-kebab. Results showed that the lateral size and thickness of kebab increased by 4.6% and 5.2%. The higher thermal conductivity in in-plane and Vicat softening temperature, increasing to 0.534 w/(mk) and 112.4 °C, were attributed to the larger region of interlocking shish-kebab throughout the pipe wall. [Display omitted] •A systematic study of HDPE pipes under shear field and annealing is reported.•The formation of dense shish-kebab increases the hoop strength at 8 rpm evidently.•The dimensional variation of shish-kebab under annealing is calculated concretely.