Deformation-Induced Crystallization Behavior of Isotactic Polypropylene Sheets Containing a β-Nucleating Agent under Solid-State Stretching

Huajian Ji, Xulin Zhou, Xin Chen, Haili Zhao, Yu Wang, Huihao Zhu, Yulu Ma, Linsheng Xie
2020 Polymers  
The deformation-induced crystallization of an isotactic polypropylene (iPP) sheet containing a β-nucleating agent was evaluated. The phase transformation of the β-modifications was investigated and the crystal morphology was observed at room temperature after stretching at different temperatures. The results showed that the crystallinity increased after solid-state stretching. When the stretching temperature was below the initial crystallization temperature, stretching deformation promoted the
more » ... rientation of amorphous molecular chains. When the deformation temperature exceeded the crystallization temperature, part of the β-modifications underwent a phase transformation process and was stretched into a shish-kebab structure. However, once the stretching temperature was close to the melting point, the β-modifications melted and recrystallized, and the shish-kebab structure underwent stress relaxation due to poor thermal stability, transforming into α-modifications. It was revealed that the crystal phase transformation mechanism of the β-modifications was based on the orientation of the molecular chains between the adjacent lamellae. In addition, the shish-kebab cylindrite structure played an important role in modifying the tensile and impact properties of the iPP sheet. The tensile and impact strengths increased by as much as 34% and 126%, respectively.
doi:10.3390/polym12061258 pmid:32486274 fatcat:opkhj4gpubfp7lut45fvcgr2ny