Technical Notebook: Properties of ultrasonically devulcanized and revulcanized used tire rubber and their blends with carbon black-filled virgin natural rubber

Continuous ultrasonic devulcanization of 40 mesh ground tire rubber (GTR) powder at a frequency of 40 kHz and ultrasonic amplitudes at 0 μm (without ultrasonic treatment) and 8 μm was carried out using an ultrasonically assisted twin-screw extruder.

Blends of GTR and devulcanized GTR with virgin natural rubber (NR) containing 60 phr of carbon black (CB) were prepared at GTR concentrations of 10, 20, 35 and 50 wt percent. The gel fraction, crosslink density, vulcanization and rheological behavior of these blends and NR/CB were investigated.

In general, gel fraction and crosslink density of vulcanized blends decreased in comparison with those of NR/CB, while their dynamic properties showed little differences until 50 wt percent. During vulcanization of blends, minimum torque was continuously increased and maximum torque was decreased only at 50 wt percent in comparison with those of NR/CB. The stress-strain behavior and abrasion loss of vulcanized blends and NR/CB were also measured.

Modulus at 100-percent elongation, tensile strength and elongation at break of blends was above 3.4 MPa, 20 MPa and 350 percent, respectively, while NR/CB vulcanizate exhibited modulus at 100-percent elongation, tensile strength and elongation at break of 3.3 MPa, 28 MPa and 470 v, respectively.

Abrasion loss of vulcanized blends containing CB was generally good, but higher than that of NR/ CB vulcanizate. Comparison of abrasion loss of current blends with our earlier study of GTR/NR blends without an addition of CB indicated that the current blends showed significant improvements in level of abrasion loss. The obtained results indicated a suitability of the utilization of ultrasonically devulcanized GTR for incorporation into new tire and rubber product formulations.