ULTRASONIC BUBBLE NUCLEATION IN REACTION INJECTION-MOLDING OF POLYURETHANE

Ultrasonic foam processing of polyurethane for reaction injection moul ding (RIM) was studied experimentally to investigate feasibility of ul trasonic bubble nucleation in polyurethane. Bubble nucleation was also studied theoretically to predict the rate of nucleation. Classical nu cleation theory and cluster theory have been employed for explanation of the nucleation phenomena. A polyol resin was saturated with nitroge n at various pressures and the pressure was released slowly in order t o generate supersaturated resin. Other components of the selected poly urethane system were added to the supersaturated resin and ultrasonic disruption was applied to the system producing enhanced nucleation. Th e ultrasonic excitation created a good foam structure even at a low sa turation pressure around 0.15 MPa (1.5 atm). The effect of the ultraso nic activation on the bubble nucleation was considered and included in the nucleation theories. The cluster nucleation theory along with con sideration of the ultrasonic effect predicted a higher rate of nucleat ion than the classical nucleation theory for the same condition.