Numerical simulation of polymethyl-methacrylate supercritical fluid foaming process: Bubble growth dynamics

Control of cell structure is an important factor of fabricating polymer foam, which is related to technological design and product performance. In this article, a multibubble growth model of polymethyl-methacrylate (PMMA) is established based on supercritical fluid foaming method and fluid simulation, aiming to analyze and predict the effects of foaming conditions (foaming temperature and foaming pressure) on the cell structures of PMMA foams. The bubble growth process is endothermic, resulting in a drop of temperature in PMMA/CO2 system, a decrease in diffusion coefficient and an increase in surface tension and viscosity, thereby preventing bubble growth. The pressure in the outer cells decreases faster than the pressure in the inner cells, causing the outer cells preferentially grow and deform, and will limit the growth of the inner cells. An empirical formula for the average cell size and foaming conditions is obtained.