Bubble‐scale observations of polyurethane foam expansion

We describe experiments designed to inform computational models of the dynamic filling process of chemically blown, polyurethane foams, especially subgrid models to predict bubble size affecting foam properties. Three experimental methods are used to observe the evolution of bubble sizes during blowing. Magnified views of bubbles at a transparent wall of a channel are recorded during the foaming. The bubble sizes in the final frame after the expansion has stopped are compared to scanning electron microscope images of the interior of the cured samples to determine wall effects. In addition, diffusing wave spectroscopy is used to determine the average bubble sizes across the width of a similar channel during foam expansion. We conclude that the bubble size distribution is dependent on the formulation of foam being tested, temperature, the height in the foam bar, the proximity to a wall, and the degree of overpacking.