Improved Control on the Microwave Devulcanizing of Ground Tire Rubber by Means of Sulphur Gas Sensors

The success of a Ground-Tire Rubber (GTR) devulcanization process relies on the elimination of the sulphur atoms that are crosslinking the rubber polymer. From the chemical point of view, this requires providing enough energy to break the sulphur bonds while preserving the carbon bonds, to ensure a high quality devulcanized GTR for being of interest to the rubber manufacturing industry. GTR is very responsive to microwaves due to the presence of Carbon Black in its composition, so the radiant energy is absorbed quickly in the form of thermal energy. When its temperature reaches 140°C, the breakage of sulphur bonds may happen under an exothermic reaction, but also some new links might be built under that condition. Therefore, from the physical point of view, the released sulphur in the gaseous form of SO₂, H₂S, and/or CS₂ must be promoted to abandon the reactor to avoid its recombination. In this work, microwave devulcanization is monitored by detecting the concentration of sulphurous gases at the exhaust of the reactor. These sensors are very effective especially when pyrometer readings are degraded because of the gaseous layer on the GTR during the process.