Foaming of Homogeneous Polypropylene and Ethylene-Polypropylene Block Copolymer Using Supercritical Carbon Dioxide

Abstract

A new process was used to foam homogeneous polypropylene (HPP) and ethylene-polypropylene block copolymer (CPP). Many different foaming behaviors of these two kinds of PP were observed. The HPP and CPP were characterized by Differential Scanning Calorimetry (DSC), and Capillary Rheometry. We find that the melt shear viscosity of CPP is more sensitive to the temperature variation than that of HPP, thus leading to larger change of cell diameter of CPP with foaming temperature. Cell size of CPP is the result of competition between cell nucleation and cell growth. When the saturation pressure is lower or higher than 25 MPa, cell nucleation or cell growth plays a dominant role, which leads to the increase or decrease of cell size, respectively. Because of its low melting temperature and crystallinity, cell diameter of CPP increases with the infiltration temperature increasing, which is opposite to those of HPP. And at the foaming temperature of 152°C or 158°C, cell diameter of CPP increases or decreases with an increase in foaming time, while that of HPP decreases with foaming time increasing at both foaming temperatures.