A Model for Rubber Degradation under Ultrasonic Treatment: Part I. Acoustic Cavitation in Viscoelastic Solid

The physics of rupture of a rubber network under the action of powerful ultrasound is considered. It is assumed that rubber degradation occurs mainly around pulsating microcavities (bubbles) usually present in rubbers. The maximal level of strain is attained in the vicinity of these cavities. A Lodge-like model of finite viscoelasticity is utilized to describe the strain profile around the vibrating cavity at a given ultrasonic pressure. Network degradation rate is taken to be proportional to the number of overstressed network chains. Detailed analysis is given for the case of a thin layer of cured rubber placed between an ultrasonic horn and a die and subjected to static pressure. Ultrasonic pressure in the layer is shown to depend on the thickness of the layer with its value found to be higher than that in the bulk. The static pressure is found to increase the ultrasonic power consumption and to enhance the degradation process. This is due to a decrease in compressibility of the bubbly media leading to a reduction in the ultrasonic attenuation. Calculations are carried out using styrene-butadiene rubber as an example.