Critical formation conditions for β-form hybrid shish-kebab and its structural analysis

Abstract

In this paper, the critical formation conditions for β-form hybrid shish kebab structure were successfully established based on the temperature/composition diagram of polypropylene (PP)/β nucleating agent (TMB-5). Furthermore, this special structure was subsequently realized in practical PP pipe processing and the multi-level and multi-scale structures were investigated comprehensively by employing various characterization approaches. The results showed that the β-form hybrid shish-kebab structure had a cylindrical symmetry where β-form lamellas were arranged in two different ways along the fibrous nucleating agent: the edge-on lamellae being parallel and the flat-on lamellae being perpendicular to the nucleating agent, indicating the double-orientation of the molecular chains. Moreover, based on the thicker flat-on lamellae and the higher ratio of flat-on to edge-on lamellae in the inner layer with slower cooling, a two order growth mechanism of the β-form hybrid shish-kebab was proposed: flat-on lamellae forming first at high temperature, followed by the formation of edge-on lamellae during the cooling process.