Control over β-form hybrid shish-kebab crystals in polypropylene pipe via coupled effect of self-assembly β nucleating agent and rotation extrusion

Abstract

In this study, tiny β nucleating agent (TMB-5) was introduced into rotation extrusion of polypropylene (PP) pipe. The experimental results showed that during the PP pipe processing, TMB-5 first self-assembled into fibrous structure and then as a template directed the epitaxial crystallization of PP into hybrid β-form shish-kebab crystals, which took the advantages of both high-strength oriented morphology and superior-toughness β-form crystal. Because reinforcing role of the anisotropic crystals strongly depends on the alignment direction, the alignment of hybrid β-form shish-kebab crystals off the axial direction was further achieved via self-designed rotation extrusion system, where the hoop drag flow caused by the mandrel rotation was superposed on the axial flow. As a result, the PP pipes with simultaneously enhanced toughness and hoop strength were prepared. When the rotation speed of mandrel was 8 rpm, the hoop strength and toughness of the PP pipe reached 34 MPa and 15.1 kJ respectively, 75% and 78% higher than those of the conventionally extruded pure PP pipes.