Sodium Sulfite/Iron Oxide‐Assisted Mechanochemical Devulcanization of Waste Tire Rubber: Structure–Property Evolution and Partial Carbon Black Substitution

Mechanochemical devulcanization of waste tire rubber (WTR) using sodium sulfite and iron(III) oxide was studied to understand how the process changes the structure and properties of the material and to evaluate the treated WTR as a partial substitute for virgin carbon black (CB). WTR was treated on a two‐roll mill using sodium sulfite/iron oxide formulations and characterized by swelling and Flory–Rehner analysis, FTIR, XPS, XRD, Raman spectroscopy, SEM/EDS, thermal analysis, rheometry, and mechanical and dynamic mechanical testing. The optimized treatment consisted of 3 phr sodium sulfite and 2 phr iron oxide. This treatment reduced the apparent crosslink density by 67.9% compared with the reagent‐free mechanically processed reference and resulted in an overall devulcanization efficiency of 82.7% compared with the initial pre‐milling WTR. XPS showed that polysulfidic sulfur decreased from 62.8% to 16.7%, and SEM revealed a rougher, microcracked surface. In rubber compounds, the treated filler gave a Mooney viscosity of 68.9 MU, close to that of the CB control (66.8 MU), and reduced the scorch and optimum cure times to 3.54 and 9.04 min. Replacing up to 35% of the virgin CB retained 91.5% of the control tensile strength, whereas 15%–25% replacement provided the closest overall balance of mechanical, wear, processing, and cure properties. The results link selective opening of the sulfur network and surface activation with improved processability, interfacial interaction, and reinforcing performance.