Experimental and simulation study of the physical foaming process using high-pressure CO2

Abstract

The simultaneous simulation of nucleation and growth of multiple bubbles was performed for a batch foaming process of low-density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS) using CO2 as a foaming agent. The simulation model involved a Blander–Katz bubble nucleation rate equation and a set of bubble growth rate equations that account for the momentum balance across the bubble interface, the diffusion of dissolved gas molecules in a polymer, and the overall mass balance of the gas in bubbles and in the polymer. The present study considered the overlapping of the concentration boundary layers. The simulation results could predict the experimental results of the bubble nucleation and bubble growth behaviors of the polymers in a fairly quantitative manner. Moreover, the effects of the physical properties on bubble nucleation and bubble growth dynamics were demonstrated in a series of sensitivity studies. The effect of interfacial tension and the diffusion coefficient strongly affected the bubble nucleation and growth rates, respectively.