The present paper describes the comparative study of a continuous ultrasonic devulcanization of ground tire rubber (GRT) using two reactors. The devulcanization zone in the first reactor (coaxial reactor) is located at the exit from an extruder without imposition of additional shearing. In the second reactor (barrel reactor), the devulcanization zone is located in barrel where additional shearing takes place due to screw rotation. Gel fraction, crosslink density, cure behavior and physical properties of GRT obtained in these two reactors were measured. Also, the distribution of gel fraction and crosslink density at various locations in the devulcanization zone of the barrel reactor were determined. Gel fraction and crosslink density show that GRT in both reactors is partially devulcanized. A unique correlation between gel fraction and crosslink density obtained in both reactors indicated that additional shearing had a positive influence on improving the efficiency of devulcanization. Under the optimal devulcanization condition, the physical properties of revulcanized GRT and the output are higher in the barrel reactor. Power consumption density in the barrel reactor is found to be significantly higher.

ABSTRACT:The recycling of carbon black (CB)-filled ethylene propylene diene monomer (EPDM) rubber was carried out by using a newly built continuous ultrasonic groovedbarrel reactor. Using this reactor, it was possible to increase by two times the output of devulcanized rubber in comparison with the coaxial reactor built earlier. The dynamic viscoelastic properties of virgin vulcanizates, devulcanized, and revulcanized EPDM rubbers were measured. The cure behavior of virgin and devulcanized rubbers was measured. The gel fraction and crosslink density of virgin vulcanizate and devulcanized EPDM rubbers, and the mechanical properties of virgin vulcanizates and revulcanized rubbers were determined. Similar to our previous findings using the coaxial reactor, the revulcanizates of unfilled EPDM rubbers of the present study showed higher mechanical properties than those of the virgin unfilled vulcanizates. However, a progressive decrease in the mechanical properties of CB-filled EPDM revulcanizates with an increase of filler concentration, attributed to partial deactivation of filler, was observed. An improvement of mechanical properties of vulcanizates was achieved upon blending the devulcanized and virgin filled rubbers.

The recycling of vulcanizates based on EPDM roofing membrane rubber using a new ultrasonic devulcanization reactor with a grooved barrel was carried out. This reactor provided continuous devulcanization at an output as high as 2.52 g/s. Die pressure and ultrasonic power consumption were measured as a function of processing conditions. The mechanical properties of virgin vulcanized and revulcanized roofing membranes were measured. Tensile strength of the revulcanized rubber was found to be similar to that of the virgin vulcanizate. Gel fraction, crosslink density, and dynamic properties of the virgin vulcanizate, the ultrasonically devulcanized rubber, and the revulcanized rubber were determined. Also, dynamic properties and the cure behavior of the virgin compound and of the devulcanized roofing membrane were investigated. All these properties were found to be dependent on processing conditions during devulcanization. The thermal stability of the virgin compound, virgin vulcanizate, and devulcanized and revulcanized rubbers were studied by means of TGA. It was found that the thermal stability of all the vulcanizates in air and nitrogen environments remained practically intact, while that of devulcanized rubber in air environment was a function of processing conditions.

ABSTRACT:The comparative study of the continuous ultrasonic devulcanization of various unfilled rubbers [natural rubber, styrene-butadiene rubber (SBR), ethylene-propylene-diene rubber (EPDM)] is carried out by means of a ultrasonic reactor. The power consumption, gel fraction, crosslink density, cure behavior, and physical properties of devulcanized rubbers were measured. The glass transition temperatures of virgin, vulcanized, and devulcanized rubbers were determined in order to characterize the difference in the mobility of rubber molecules for each rubber before and after devulcanization. Thermogravimetric analysis was also used to determine thermal stability of the various rubbers. A unique correlation between gel fraction and crosslink density indicated significant differences in the efficiency of devulcanization of various rubbers. Under certain devulcanization conditions, the mechanical properties of revulcanized SBR and EPDM rubbers were found to improve compared to those of the original rubbers.

This paper describes the results of an extensive study involving the continuous ultrasonic devulcanization of unfilled EPDM rubber. Die pressure and ultrasound power consumption were measured as a function of processing conditions. The mechanical properties of aged and fresh revulcanized EPDM rubber were measured. Gel fraction, crosslink density, and dynamic properties were also determined for the virgin vulcanizate, the ultrasonically devulcanized rubber, and the revulcanized rubber. Additionally, the cure behavior of virgin and devulcanized EPDM rubber was investigated. The tensile strength of revulcanized EPDM rubber was found to be much higher than that of the virgin vulcanizate with the elongation at break being practically intact. A mechanism explaining the increase in mechanical properties of revulcanized rubbers was proposed.