ABSTRACT
Degradation.................................................................................390 9.12 Conclusions ...............................................................................................394 Acknowledgments ..............................................................................................394 References.............................................................................................................395
A recent method for recycling thermosets is with the application of ultrasound, by which waves of certain levels, in the presence of heat and temperature, can rapidly break down the three-dimensional structure of crosslinked rubber, making it reprocessable. This chapter provides an up-to-date account of ultrasonic devulcanization of rubbers, including the history of the technology, available reactors, extensive experience accumulated with various types of rubber, attempts to develop mechanisms of devulcanization, and models to theoretically describe the process and a possibility of its scale-up. The chapter gives a comparative analysis of process characteristics, rheological and mechanical properties, structural transformations, curing behavior and nuclear magnetic resonance (NMR) relaxation, and diffusion processes taking place in unfilled and filled rubbers during their ultrasonic treatment. Properties of blends of devulcanized and virgin rubbers are also presented. Sulfur-and peroxide-cured rubbers are considered, along with details of degradation mechanisms of the rubber network by ultrasonic waves. Future directions and further development of ultrasonic devulcanization technology are also discussed.
