Optimization of Ultrasonic Devulcanization of Cryo-Ground Tire Rubber

The ultrasonic devulcanization of a cryo-ground tire rubber in a co-rotating twin-screw extruder was studied and optimized using the response surface methodology. The devulcanization process was investigated using several responses, including crosslink density, gel fraction, complex viscosity of devulcanized rubbers and tensile strength, modulus and elongation at break of revulcanized rubbers. The dependence of each experimental response on the process variables (ultrasonic amplitude, temperature, screw speed and flow rate) was modeled applying a second order model and the coefficients were calculated by multiple linear regression. Reduced regression models and responses surfaces were obtained for each response, considering only the significant variables and interactions. The results predicted by these models showed good agreement with the experimental values. The experimental responses were influenced by a different set of variables and interactions. The ultrasonic amplitude was found to be the most effective variable influencing the devulcanization process and the mechanical properties.