Improving the mechanical and thermal properties of shish-kebab via partial melting and re-crystallization

Abstract

A fully oriented isotactic polypropylene (iPP) sample containing a large amount of shish-kebab was molded by multiflow vibrate-injection molding. When annealing was performed at a temperature close to the melting temperature of the shish-kebab, thin-kebab can be melted and release chains to the amorphous phase. The released oriented chains can reduce the concentration of the molecule entanglements and facilitate the molecular chains to rearrange on the thick-lamella. Partial melting and re-crystallization greatly enhanced the thermostability and mechanical property of the shish-kebab. In situ small-angle X-ray scattering and wide-angle X-ray diffraction were performed to elucidate the melt-recrystallization process. Results showed that annealing at 165 °C can melt thin kebab but thicken the thick kebab, and the kebab grew in only one dimension. By restructuring and perfecting the shish-kebab, melting temperature and impact strength increased about 10 °C and by 158%, respectively. We focused on the complex melting–recrystallization processes and provided a theoretical basis for the high-efficient, time-saving annealing method.