Evolution of Polymorphic Structure in β-Nucleated Isotactic Polypropylene under a Certain Pressure: Effects of Temperature and Flow

Isotactic polypropylene (iPP) is one of the most intensively investigated polymeric materials for a long time because of its special polymorphism. In this work, the effects of temperature and flow on the evolution of polymorphic structure in β-nucleated iPP under 100 MPa were studied by X-ray scattering techniques and differential scanning calorimetry (DSC). It was found that the evolution of polymorphic structure in iPP could be divided into four regions in terms of the shear strength under different temperatures: region I (0 s–1, static condition), β/γ crystalline system with dominant β-form; region II (0–13.8 s–1, weak shear), α/β/γ crystalline system; region III (13.8–18.3 s–1, medium shear), α/γ crystalline system with dominant α-form at a low crystallization temperature (150 °C) while with dominant γ-form at a high crystallization temperature (180 °C); region IV (18.3–21.3 s–1, strong shear), α crystalline system at 150 °C while γ crystalline system at 180 °C. These results could afford guidance in ...