Recycling of rubber wastes by devulcanization

[Display omitted] •Waste tires management is an environmental problem and a technological challenge.•The best way to eliminate the rubber wastes is through recycling by devulcanization.•Thermomechanical devulcanization is the most suitable industrial method.•Combining scCO2 with thermomechanical treatment promotes the recycling of rubbers. Disposal of used tires and rubber wastes is one of the biggest challenges of the 21st century waste management. One of the environmentally friendly possibilities of recycling this type of material is to go through the breaking of their three-dimensional structure. This treatment, called the devulcanization, can be defined as a process that causes the selective breakup of the sulfur-sulfur (S-S) and carbon-sulfur (C-S) chemical bonds without breaking the backbone network and without degrading the material. The devulcanized rubber can be mixed with virgin rubber or with other kinds of matrices to give new compounds without generating a significant decrease in mechanical and physical properties. Many devulcanization process types are presented in the literature: chemical, ultrasound, microwave, thermomechanical, etc. The thermomechanical devulcanization based on extrusion seems to be the more suitable to be applied on an industrial scale. The supercritical CO2 has been proposed as a green atmosphere that can be used to improve this type of devulcanization. In fact, it seems that in supercritical conditions, the CO2 swells the rubber and stretches the sulfide links, making them easier to break. This paper presents a literature review on rubbers recycling by devulcanization. It is focused on the different devulcanization techniques used in the last decades. Particular attention is paid to the thermomechanical method, those in the presence of supercritical CO2 and, finally, the combined thermomechanical process with supercritical CO2 atmosphere.