(105f) Polyurethane Foam Expansion, Polymerization and Bubble Pressurization

In this presentation, we discuss our new, experimentally driven, approach to foam expansion and polymerization modeling. We are working to develop high-fidelity computational models to be used to design and troubleshoot mold filling for polyurethane structural foam parts. We are studying PMDI polyurethane with a fast catalyst, such that filling and polymerization occur simultaneously. The foam is over-packed to twice or more of its free rise density, to reach the density of interest. Developing a relevant model to represent the expansion, filling, curing, and final foam properties is quite challenging. PMDI is chemically blown foam, where carbon dioxide is produced via the reaction of water and isocyanate. The isocyanate also reacts with polyol in a competing reaction, which produces the polymer. A new kinetic model is implemented, which follows a simplified mathematical formalism that decouples these two reactions. The model predicts the polymerization reaction via condensation chemistry, where vitrification and glass transition temperature evolution must be included to correctly predict this quantity. The foam expansion kinetics are determined by tracking the molar concentration of water and carbon dioxide in both the gas and polymer phases. A bubble-scale mathematical model has been developed that looks at the super saturation of carbon dioxide in the polymer and the concomitant bubble pressurization. The model is calibrated with bubble-expansion data from bubble growth experiments. It is used to predict the density of a foam bar and compared to to Xâ??Ray CT data.