The effect of annealing time on morphology, mechanical properties, and thermal conductivity of HDPE pipes produced by rotational shear

Abstract

The high-density polyethylene (HDPE) pipes containing a large amount of shish-kebab structures were produced by a self-developed rotational shear system (RSS). The effect of different annealing time on morphology, mechanical properties, and thermal conductivity of HDPE pipes with shish-kebab structures was studied. The results showed that there were two models for the change of shish-kebab structures after annealing at 125 ℃: partial melting and annealing recrystallization under short-term annealing conditions (< 120 min), and new elongated kebabs formation under long-term annealing conditions (≥ 120 min). Under short-term annealing conditions, the hoop tensile strength increased by 2.21% and thermal conductivities in both directions also increased slightly. However, under long-term annealing conditions, the hoop tensile strength increased by 19.12% (from 73.56 MPa to 87.63 MPa), and the thermal conductivity of out-of-plane increased by 7.77% due to the higher interlocking degree of shish-kebab.