High‐pressure induced formation of isotactic polypropylene mesophase: Synergistic effect of pressure and pressurization rate. Issue 3 (17th October 2018) - Huang, Jingjing
Abstract : The crystallization induced by high pressures up to 2 GPa was studied for isotactic polypropylene (iPP) using wide angle X‐ray diffraction, small angle X‐ray scattering, and atomic force microscopy methods. The iPP mesophase can be induced at 200°C by high pressures with fast pressurization rate. A pressure–pressurization rate kinetic phase diagram of mesophase and γ‐phase was established to systematically analyze the influences of pressure and pressurization rate on crystallization polymorphism. Under pressure not higher than 0.75 GPa, only γ‐phase is formed, even the pressurization rate reaches 5 × 10 3 MPa/s. With increasing pressure to 1.0 GPa, the mesophase is possible to be generated. As pressure further increases to 1.5 GPa and higher, the pure mesophase system can be obtained for pressurization rate above the critical values (about 10 MPa/s). Moreover, the structure of iPP mesophase obtained by rapid pressurization was analyzed and compared with that prepared by temperature quenching. Also interestingly, the pressure‐induced mesophase can transform into γ‐phase by annealing under pressure at 200°C, and the rate of this phase transition is slowed down with increasing annealing pressure. POLYM. ENG. SCI., 59:439–446, 2019. © 2018 Society of Plastics Engineers