Pressurization induced crystallization of iPP containing self-assembly β-nucleating agents: role of pressurization rate and temperature

Abstract

Pressurization-induced crystallization (PIC) of isotactic polypropylene (iPP) with the β-nucleating agent (β-NA) was investigated by wide-angle X-ray diffraction, polarizing microscopy and differential scanning calorimetry measurement. A competitive formation process between the mesophase and γ-iPP was found in the PIC process. Specifically, increasing the pressurization rate can significantly suppress the formation of γ-phase and induce the formation of mesophase with the range between the critical pressurization rate from R₁ to R₂, however, when the temperature exceeds a critical value of about 280 °C, only mesophase forms despite any pressurization rate. Moreover, instead of β-iPP, β-NA serves as an effective nucleating agent and promotes the formation of γ-iPP under PIC treatment, and its self-assembly morphology can also be controlled by verifying pressurization rates and/or temperatures. As a result, a reasonable mechanism was proposed to show how to tune the crystalline polymorphism and morphology of iPP materials by using the “pressurization” method, and a pressure-temperature crystallization structural diagram was established to analyze the synergistic effect of pressurization rate and temperature on the crystallization polymorphism of iPP. It demonstrates that pressurization is likely to be a universal method for tailoring polymer crystallization within an appropriate temperature range.