Effect of Foaming Temperature on Cell Structure of Foamed Polypropylene Using Supercritical CO2

The foamed PP was prepared by using supercritical CO2 with selfmade high meltstrength polypropylene as starting material. Effect of foaming temperature on cell structure was studied. The results indicate that a suitable foaming temperature zone, from 155 ℃ to 170 ℃, was gained. Cell density increases gradually with the decreasing of foaming temperature, while average cell diameter changes along the opposite trend. When the foaming temperature is 160 ℃, cell density, average cell diameter and apparent density are 1.03×107 cell/cm3, 73.86 μm and 0.016 g/cm3 respectively. Furthermore, foam expansion ratio reached the largest, about 55 times. Foaming temperature controlled the cell structure and foam expansion ratio by influencing the crystallization rate, viscoelasticity as well as the solubility and diffusivity of the blowing agents in the polypropylene melt.