Molecular dynamics simulation and experimental study on crumb waste rubber devulcanization using waste oils

To investigate the devulcanization process of crumb waste rubber (CWR) in waste oil, the study examines the influence of medium temperature, waste oil mass ratio (including waste engine oil (WEO) and waste cooking oil (WCO)), and the mesh size of crumb waste rubber on the devulcanization process under a constant reaction time. Subsequently, a molecular dynamics (MD) simulation was conducted after determining the optimal variables for devulcanizing CWR with waste engine oil (DCREO) and waste cooking oil (DCWRCO). Increasing the medium temperature and the dose of waste oil to the CWR with an 80-mesh size resulted in a more de-cross-linked structure, indicating significant structural changes. This demonstrates that devulcanization occurs effectively at medium reaction temperatures, leading to a substantial reduction in carbon, hydrogen, and sulfur elements within the rubber hydrocarbon. Furthermore, alterations in the hydrocarbon peaks of CWR in XRD data were observed, manifesting as new peaks 37°. MD have revealed that the properties of devulcanized mixtures (DCWREO and DCWRCO) exhibit stability in terms of density and energy, despite variations in waste oil content. This study contrasts the WEO-CWR and WCO-CWR systems, emphasizing their respective densities and interactions. In the WEO-CWR system, the density is measured at 755.94 kg/m3, with a van der Waals energy of −17979.0 kJ/mol and weak electrostatic interaction of 722.48 kJ/mol. Conversely, the WCO-CWR system displays a density of 745.36 kg/m3, a van der Waals energy of −17908.0 kJ/mol, and an electrostatic interaction of 1160.1 kJ/mol. The prevalence of hydrophobic interactions in the CWR systems is attributed to the absence of polar functional groups, while hydrogen bonding is facilitated by carboxyl groups. Furthermore, this investigation offers insights into the underlying mechanisms driving the observed variations in all properties. © 2024 Elsevier B.V.