Continuous Devulcanization of Ground Tire Rubber of Different Particle Sizes Using an Ultrasonic Twin-Screw Extruder
Continuous ultrasonic devulcanization of ground tire rubber (GTR) of 10 mesh and 30 mesh from Rondy Co., as well as whole truck tire rubber of 40 mesh (40TR), 140 mesh (140TR), 200 mesh (200TR), mixture of 40 and 80 meshes (84TR) and truck tire buffing rubber of 80 mesh (80BU) from Lehigh Technologies, Inc. were studied. The devulcanization process was conducted using an ultrasonic co-rotating twin-screw extruder at ultrasonic amplitudes from 5 to 13 µm and a frequency of 40 kHz. Ultrasonic power consumption and die pressure during devulcanization, curing behavior of devulcanized rubber, gel fraction and rheological properties of devulcanized and revulcanized rubbers, crosslink density and mechanical properties of revulcanized rubbers were obtained. It was found that GTR of 10 mesh devulcanized less than GTR of 30 mesh. Similarly, GTR of 40TR experienced less devulcanization than that of 84TR. This effect is attributed to a higher surface area in finer particles. Two groups of devulcanized rubbers exhibiting the smooth and rough extrudates were observed during the devulcanization of GTR of 10 and 30 meshes. The smooth extrudates were obtained at higher amplitudes due to more devulcanization. The revulcanizates of smooth extrudates had a higher elongation at break, but a lower modulus at 100% elongation and tensile strength. The devulcanized and revulcanized rubbers of 140TR were found to have a lower gel fraction than the devulcanized and revulcanized rubbers of 200TR. The elongation at break, modulus at 100% elongation and tensile strength of the revulcanized rubber of 140TR were found to be lower compared to those of the revulcanized rubber of 200TR. Gel fraction measurement indicated that the devulcanization of GTR of 30 mesh, 40TR and 200TR increased with an increase of the ultrasonic amplitude. In contrast, 84TR and 140TR exhibited less devulcanization at intermediate amplitudes due to prevailing effect of revulcanization over devulcanization. The 80BU was found to be less sensitive to ultrasonic treatment than other GTR with structures and properties of the devulcanized rubber being less dependent on ultrasonic amplitudes. Among various GTR, the revulcanizates of 80BU exhibited the highest elongation at break and tensile strength.
Polymers, Continuous ultrasonic extrusion, Devulcanization, Ground tire rubber, Particle size, Recycling, Reclamation, Waste rubber, Ultrasound, Twin-screw extruder, Swelling test, Gel fraction, Crosslink density, Rheology, Mechanical properties, Curing curves
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