Significance of Ultrasonic Cavitation Field Distribution in Microcellular Foaming of Polymers

In this study, the influence of field distribution of ultrasonic waves on the manufacturing of microcellular Acrylonitrile-Butadiene-Styrene (ABS) foam was investigated. In the primary studies, Aluminum foil erosion tests were performed to analyze the spatial field distribution of ultrasonic waves throughout the water bath. It was found that there exists a critical effective distance from the ultrasonic transducer where the maximum cavitation intensity can be achieved. Prior to and beyond this critical effective distance, the cavitation intensity reduces drastically. In the succeeding study, gas saturated polymer pellets were placed inside the ultrasound medium at various effective distances from the transducer for a predefined amount of treatment time and then were microcellular solid-state batch foamed. Intense cell nucleation phenomenon was observed in samples sonicated at the critical effective distance, while at other distances a very mild increment in cell density was observed. The expansion ratio and cell morphology was also found to be significantly affected by the relative placement of gas-saturated polymer with respect to the transducer in sonication medium.