A novel online visualization system for observing polymer extrusion foaming

Cell nucleation and premature cell growth in extrusion foaming are critical to elaborate the morphology of final foams. These courses happen in the extrusion die which has been unknown for real extrusion foaming process. In this study, a novel visualization system was developed to online observe the cell nucleation and evolution behavior in the extrusion die. The cell evolution and real time pressure along the flow direction could also be obtained with the system. It was found that the solution pressure Psolution was influential to the critical nucleation radius Rcr and the nucleation rate N0. The higher screw rotating speed corresponded to higher Psolution, lower in die N0 and less premature cells, while higher cell density for extrude foams. In addition, premature cells with radius over critical break radius Rcrb would break into several small cells under sufficient stress gradient in the extrusion flow field.