DEVULCANIZATION OF WASTE TIRE RUBBER BY POWERFUL ULTRASOUND

Ground rubber tire (GRT) is devulcanized in a continuous process where the rubber crumb is conveyed by a screw extruder to a thin gap betwee n a stationary die and a vibrating horn. Ultrasound amplitude, gap thi ckness and the duration of the treatment are varied, and their effect on the rubber properties is studied. The degree of devulcanization is characterized by the crosslink density and gel fraction of the devulca nized rubber. These characteristics are found to correlate uniquely wi th each other over a wide range of the treatment conditions. The speci fic energy of ultrasound consumed per unit mass of the rubber is found to be the operating parameter correlating with the properties of the devulcanized rubber. The mechanical properties of the re-vulcanized sa mples reach a maximum with an increasing degree of devulcanization, an d then drop as a result of excessive degradation. Even without optimiz ation of cure recipes, tensile strength and ultimate elongation of re- vulcanized tire rubber as high as 10.5 MPa and 250%, respectively, are achieved.