C2C Technology for Passenger CAR Tire Rubber By a Continuous Devulcanization Process

As a means for decreasing the amount of waste tires and for re-using tire rubber for new tires, devulcanization of ground passenger car tires is a promising approach. Being an established technology for NR and EPDM, earlier work has shown that for ground passenger car tire rubber with a relative high percentage of SBR, a devulcanization process can be formulated too. This was proven for a laboratory scale batch process in an internal mixer, using diphenyl disulfide as devulcanization aid and powder-sized material.

In this study, the devulcanization process for passenger car tire rubber is further scaled up and transformed into a continuous process in a co-rotating twin-screw extruder. As SBR is rather sensitive to devulcanization process conditions such as thermal and mechanical energy input, the screw design was based on a low shear concept. A granulate with a particle size from 1 to 3.5 mm was a chosen as feedstock.

The devulcanization was fine-tuned in terms of:

• Process conditions: time/temperature profile, concentration devulcanization aid

• Extruder parameters: screw configuration, screw speed, fill factor

• Ancillary equipment: pre-treatment, extrudate handling

In this paper, the influence of these parameters on the devulcanization efficiency and the quality of the final product will be discussed. The ratio of random to crosslink scission as determined by a Horikx plot was taken for the evaluation of the process as well as the material. A best practice for a continuous devulcanization process in this type of extruder will be given.