Real-time monitoring of ground-tire rubber microwave devulcanization with thermal and electrochemical sensors

Devulcanizing ground-tire rubber (GTR) properly requires the removal of the sulphur linkages that crosslink the polymer. The volatile sulphur compounds (VSCs) released during the process must be extracted from the reactor to avoid any chemical recombination, and the sulphur gas concentrations conveniently sensed during the extraction, along with a thermal sensoring of the payload, can be used to monitor the whole devulcanization process. In this contribution, a modified conventional microwave oven was used to devulcanize the GTR. The microwave-processed GTR was evaluated by determining the values of its mass loss (ML), soluble fraction (sol fraction), and the variation of its electric permittivity. Results show a direct relationship between the energy delivered, sol fraction, the VSCs concentrations, the ML, and the permittivity values. Thus, this paper demonstrates that monitoring the VSCs can provide a reliable indication of ML and, consequently, devulcanization evolution even at non-uniform temperature conditions.