## 1 Introduction  
Today, plastics and rubbers are widely used in different applications, and this is why the recent decades are sometimes called the \"plastic age\" [1]. One of the most prominent examples of this increasing trend is the production and uses of rubbers (natural and synthetic). In 2019, the global rubber and tire market grew by 4% to reach a volume of 3 billion tires [2]. Large amounts of rubbers are used to produce tires for airplanes, cars, trucks, etc. However, after the end of their service life, only a very limited amount of rubber (1%) is lost from the original tire [3]. This indicates that a large amount of rubber can still be used for other applications. Residual rubbers belong to the group of non-environmental resources as they are insoluble and infusible (highly cross-linked material). They also cannot return to the environment via usual biodegradation. So, the problem of waste rubber management becomes critical, and solutions must be proposed to use this material available everywhere on the planet. The main problems associated with the recycling or recovery of scrap tire rubbers are associated to their complex structures made from cross-linked rubbers with steel and polymer fibers (cellulose, nylon, and polyester) as reinforcement. So, each component must be separated from the rubber during a mechanical recycling process. It is known that 12 components at minimum are used in a passenger vehicle tire, while a truck tire has about 20 components [4]. In general, styrene-butadiene rubber (SBR) is used to produce passenger tires, while natural rubber (NR) is the main component for truck tires [5]. Table 1 presents the typical compositions of different tire structures. Due to increasing environmental concerns, a great deal of work has been undertaken to develop tire recycling methods (devulcanization/regeneration) and to find applications for these waste rubber products [7; 8]. Hence, various techniques/methods have been proposed to reduce the high amount of waste rubbers. One of the most useful techniques, at least as a starting point, is grinding (particle size reduction) to use the resulting ground tire rubber (GTR) in polymer compounds (blends, composites) as a filler (active or not) or as an impact modifier to improve the elasticity/ductility/toughness of a neat resin (thermoplastic or thermoset). For instance, ground tire rubbers can be introduced into thermoplastic resins to produce thermoplastic elastomers (TPE) [9]. The main matrixes studied so far are polyolefins (polyethylene and polypropylene). Recently, the market for these materials has grown because TPE can be reprocessed and recycled using standard thermoplastic (melt) processes. However, several studies have reported that the addition of a rubber phase into a thermoplastic matrix results in lower overall mechanical properties (stiffness and strength) [10]. Lower mechanical properties of TPE in industrial applications such as O-rings and insulators in the oil and gas industry, or rubber gaskets for window, door, and gas seals in the automotive industry, can lead to lower safety and shorter product life. These materials have the advantages of both thermoplastics and elastomers, such as mechanical properties similar to those of elastomers and the processability of thermoplastics. However, as for most immiscible multicomponent systems, interfacial compatibility/adhesion becomes an issue; this is also reported for other composites like ceramic and metal composites [11; 12]. One way to increase the compatibility between the components is GTR chemical modification by reducing the degree of cross-linking (devulcanization/regeneration), at least on the particle surfaces, because a high degree of cross-linking hinders chain mobility (molecular diffusion) and prevents molecular interaction between the matrix and GTR. Another important parameter is the particle size distribution controlling the degree of phase separation or interfacial properties modifying the interfacial contact area.