Rubber-iron interface separation using liquid nitrogen for material selective recycling and its mechanism

Rubber-metal composites combine elastic rubber with metals to achieve functions such as impact resistance, vibration damping, and sealing performance. Their separation is important for material recycling and proper treatment of rubber, which is difficult to decompose naturally. However, separation technologies remain underdeveloped due to strong vulcanized bonding and the limitations of thermal and mechanical processes. In this study, cryogenic cooling by liquid nitrogen immersion was investigated as a non-heating interface separation method, and its mechanism was clarified. In the specimen used in this study, interfacial separation was observed after approximately 60 s of immersion in liquid nitrogen at 77.15 K. Observations of the separation behavior and residual rubber patterns suggested that separation proceeds through crack propagation initiated near the corners of the bonded interface after the glass transition of the rubber. Thermal stress simulations indicated significant elastic strain energy concentration at the interface corners. The results also suggested that separation strongly depends on the thickness and geometry of the rubber layer, which govern the magnitude of energy concentration. In addition, a higher Young's modulus of the metal was found to enhance energy concentration and promote separation. These findings indicate that cryogenic cooling is a promising separation method for rubber-metal composites without hazardous gas generation associated with heating.