Thermodynamic behavior and crystal structure of polypropylene treated with supercritical carbon dioxide

Abstract

Abstract Controlling temperature and pressure during the supercritical carbon dioxide (scCO2) process can change the mount of CO2 entered in polypropylene (PP) phase, thereby changing the mechanical properties of materials. The effect of scCO2 treatment on the crystallization behavior is different in the semi-molten and molten states. This study investigates the PP treated with scCO2 near the melting point and at various pressures, and explores the effects of temperature and pressure on the crystal structure, lamellar structure, and thermodynamic properties of PP. The results show that at a melting temperature of 165 °C, scCO2 can enhances the ability of PP molecules to makes the PP crystal region more regular, and forms larger microcrystals and lamellae. Additionally, increasing the pressure can make more CO2 enter the PP crystal region and further improve the regularity of the crystal. At a semi-melting temperature of 155 °C, scCO2 is primarily in the amorphous region because it is difficult to enter the PP crystal region. Even if increasing the pressure, it has little effect on the crystal size and lamellar thickness of PP. The research has significant implications for developing and utilizing scCO2 to remove ash from materials.