Effect of a Polypropylene Skin on the Hardness of Polyethylene Pipe

Abstract

This paper investigated the effect of outer polypropylene (PP) skin thickness on the density and calculated hardness of a polyethylene (PE) core pressure pipe. Density of PE pipes with different PP skin thicknesses (including a PE pipe without a skin) was compared and found that the density distribution can be described well by an exponential function and it increased and flattened with increased PP thickness, which was equivalent to a PE layer 2~3 times as thick. Thermal analysis showed that the density increment is derived from the thermal insulation provided by the PP skin and allowed annealing occur during pipe cooling, particularly close to the outer wall. According to the crystallinity and hardness relationship, the relative strengthening effect on hardness and its relationship with PP layer thickness was quantified.