The influence of melt temperature on the crystal orientation of polypropylene containing talc

Abstract

Constructing oriented crystals in products is one of the effective means to endow semi-crystalline polymers with high performance or special function. For polypropylene (PP), introduction of flake-like talc is a feasible method to induce the formation of oriented PP crystals. In this work, the influence of melt temperature (Ts) on the crystal orientation of talc-filled PP was investigated by characterizing the crystal orientation of PP containing in-plane oriented talc after cooling from different Ts located at Domain I and Domain II. It was found that the crystal orientation of sample remarkably varied at different Ts, in which it kept stable in Domain I, while increased and then decreased in Domain II with decreased Ts. By analyzing the nuclei at different Ts, a probable mechanism for varied crystal orientation at different Ts was proposed: In Domain I, only inherent foreign substances and talc existed in the melt, where the former and the latter induced the formation of isotropic and oriented PP crystals, respectively. In high temperature range of Domain II, some oriented crystal fragments stabilized by talc also survived in melt leading to the generation of oriented PP crystals. In low temperature range of Domain II, in addition to the oriented crystal fragments, some isotropic one remained in melt resulting in the formation of isotropic PP crystals. The competitive growth of these various kinds of nuclei at different Ts determined the final crystal orientation of talc-filled PP.