Science and Technology of Ultrasonic Devulcanization of Rubbers

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The main objective of this research project is to develop basic knowledge and to design high capacity equipment for the new technology of continuous devulcanization of different kinds of reinforced and nonreinforced vulcanized elastomers. Through the application of certain levels of ultrasonic amplitudes in special devices, the three-dimensional network can be broken down within a short period of time of the order of a second or even less. As the most desirable consequence, ultrasonically treated rubber becomes soft thereby enabling this material to be reprocessed, shaped, and revulcanized. Under certain processing conditions, the tensile strength of revulcanized rubber is much higher than that of original vulcanizates. This study outlines a series of experiments to (1) identify the effect of the chemical structure of vulcanized rubber on the devulcanization process; (2) evaluate the effect of the type and amount of filler on the devulcanization process; (3) investigate the effect of the ratio of bond energy of the main chain and that of crosslinks and rubber-filler bonds on the break up of the three dimensional rubber network; (4) establish optimal conditions for the devulcanization and revulcanization process enabling one to obtain reclaimed rubbers with better mechanical properties; (5) design new equipment for continuous devulcanization of vulcanized elastomers; and, (6) develop the theory of ultrasonic devulcanization based not only on the process of cavitation collapse but also accounting for the network degradation owing to dynamic fatigue in the vicinity of stable pulsating cavities. Since the dynamic fatigue processes are specific to polymer chemical structure as well as to rubber network topology, the theory may be able to predict optimal conditions of ultrasonic devulcanization for different types of crosslinked rubbers. The development and application of this novel technique for reclaiming all industrially important types of rubber, including tire rubber, will have a signific ant impact on the further expansion of recycling technology. Development of a theoretical model of the process of ultrasonic devulcanization, allowing one to predict optimal conditions of recycling, will help to devise a methodology to control the properties of reclaimed rubber products. The new science-based technology can revolutionize the way rubber is recycled.