Processing of cellular polyurethane was investigated experimentally and theoretically to examine the possibility of ultrasonic foaming. Polyol resin was supersaturated with nitrogen and ultrasonic excitation was applied for copious bubble nucleation. The ultrasonic excitation resulted in good foam structure whose size distribution was uniform and less than 100 μm. The ultrasonic excitation was modelled by utilizing the classical nucleation theory to predict the rate of nucleation. Theoretical results suggest that a high rate of nucleation will be obtained if the ultrasonic excitation generates large enough negative pressure. Final bubble size was calculated by considering the pressure equilibrium between inside and outside of the bubble.

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