Effect of supercritical carbon dioxide-assisted nano-scale dispersion of nucleating agents on the crystallization behavior and properties of polypropylene

This work aims at using supercritical carbon dioxide (scCO2) to disperse a nucleating agent, sodium 2,2-methylene-bis (4,6-di-tert-butylphenyl) phosphate, denoted as NA40, in an isotactic polypropylene (PP) on the nanometer scale and at studying the nucleating efficiency of the nano-dispersed NA40 by differential scanning calorimeter (DSC) and polarized optical microscope (POM). The Avrami equation and a model combining Avrami equation and Ozawa equation were used to describe the isothermal and non-isothermal crystallization kinetics of the nucleated PP, respectively. The results showed a consistent trend: both the isothermal crystallization rate and the non-isothermal crystallization temperature of the PP in which NA40 was dispersed under scCO2 were higher than those of the virgin PP and the PP in which the same amount of NA40 was incorporated by a classical extruder compounding process. Moreover, the size of the spherulites and the haze of the former PP were smaller than those of the virgin PP and the latter. The trend was reversed in terms of flexural and tensile strengths.