The Influence of Pressure Environment on the Cellular Morphology of Foamed Polypropylene and Finite Element Simulation

ABSTRACT Through a visualized injection molding device, the effects of melt pressure and gas counter pressure (GCP) on cell morphology were investigated. The results indicated that under low melt pressure, cell deformation intensified. Increasing the melt pressure reduced the cell deformation degree from 0.16 to 0.05. The application of GCP improved pressure uniformity, maintaining deformation degrees generally below 0.06. Furthermore, increasing gas pressure exhibited a continued reduction trend in deformation degree, demonstrating that GCP can significantly mitigate cell deformation. Finite element simulations revealed the influence of melt pressure on cell deformation. As melt pressure increased from 0 to 200 Pa, the stress difference between transverse and longitudinal directions decreased from 370 to 270 N/m 2 , where stress inhomogeneity around adjacent cells induced transverse deformation. Meanwhile, the difference between the longitudinal and transverse displacements of the melt surrounding the cell decreased from 14.3 to 7.1 μm. This displacement difference in the melt induces longitudinal deformation of the cell structure. Enhanced melt pressure improved stress uniformity around cells and reduced melt migration distance, thereby decreasing degree deformation. The simulation results aligned well with cell deformation behaviors observed in visualization experiments.