## 1 Introduction  
In recent years, the use of carbon fiber-reinforced polymers (CFRPs) has increased in a variety of sectors, and particularly in the aeronautics industry, because of their exceptional mechanical strength, stiffness, fatigue resistance, lightweight composition, and ability to withstand high temperatures and the action of chemicals. Global market demand for CFRPs has grown from 68 kilotonnes in 2010 to 170 kilotonnes in 2020, and it is estimated that it will exceed 190 kilotonnes by 2050 [1, 2]. We are currently facing a series of challenges in relation to the management of the CFRP wastes generated, which can be divided into two categories: those generated during the manufacturing process (offcuts, which account for 40% of the CFRP used in the industry) and those that result after the end of the useful life of the manufactured components. In any case, the recycling of CFRPs is a major problem still to be solved, since a large part of the generated waste is currently either disposed of in landfills or incinerated. Such solutions are unsatisfactory, from both the environmental and the economic point of view, and fail to meet both legal and social demands. Global CFRP waste generation is estimated to reach 20 kilotons per year by 2025 [3, 4]. Composite materials are the result of combining two or more constituents with a strong interface between them [5] so that they can exhibit superior properties than those corresponding to each individual constituent on its own. Composite materials normally consist of a matrix, that binds and shapes the composite material, and a reinforcement element that provides stiffness and strength. Depending on the material used for the matrix, they can be metallic, ceramic, or polymeric. Depending on the reinforcing element, they can be fiber-reinforced, particle-reinforced, or fabric-reinforced composites [5; 6; 7]. Epoxy resins are thermosetting polymers. This means that after their cross-linked molecular structures have been formed as a result of their curing process, they cannot be recycled using standard methods, nor can their structure be reshaped. These structures are actually the ones that confer the polymer with its thermal and dimensional stability as well as its high mechanical strength. Epoxy resins exhibit average density values of 1.1-1.4 g/cm\({}^{3}\), Young's modulus of 3-6 GPa, tensile strength (TS) of 35-100 MPa, and a deformation at failure of 1-6% [5; 6]. These resins that are used today should be recycled when they reach the end of their useful life, which is why it is necessary to develop an optimal recycling process [8]. Carbon fibers (CFs) offer high fatigue strength levels, low coefficients of linear thermal expansion, and low corrosion susceptibility. Their main average mechanical properties are their density of 1.5 g/cm\({}^{3}\), Young's modulus of 151 GPa, and tensile strength (TS) of 2500 MPa [5; 6]. On the other hand, they have a low impact resistance and a high electrical conductivity. Thermosetting composites are difficult to recycle because of their cross-linked molecular structures. In particular, thermosetting resins such as epoxy cannot be easily depolymerized to their initial monomers, and therefore, conventional techniques such as those described below cannot be successfully applied to the recycling of this type of polymer [3]. Given that the manufacturing of virgin carbon fibers is a costly and energy-intensive process, which may also produce dangerous gases that are harmful to both health and the environment, the development of new recycling methods for the recovery of carbon fibers is of particular interest [1; 9]. The different techniques that are currently used for the recycling of CFRPs can be mainly classified as mechanical, thermal, or chemical. The mechanical recycling techniques involve the size reduction of the composite material by crushing or fracturing. Quick processing speed and a straightforward scalability of their operating conditions are among their key advantages.