## 1 Introduction
The last trends in TR waste vaporization, where complex multi-step chemical procedures and organic solvents are avoided, present the additive manufacturing techniques for their fast-prototyping advantages of devices with desirable final properties. Furthermore, the 3D printing technology is also considered as an eco-friendly beneficial approach for printed materials with complex geometries that can be partly or entirely made of recycled resources, without the use of mold tooling. For example, recycled ground TR modified with 3-(trimethoxysily)propyl methacrylate was used as ink in the elastomeric matrix for direct printing. The resulted composites were defined as cheaper compared to the equivalent polymer specimens, with mechanical properties close to the molded references [11]. Drop-on-demand-based inkjet was used for the fabrication of multilayer latex-based materials loaded with micronized end-of-life tire rubber, with preserved Young's modulus of the printed specimens [12]. Between the available additive manufacturing technologies, selective laser sintering (SLS) is one of the most attractive from industrial and academic points of view. SLS is offering an additional level of flexibility in terms of devices prototyping with desired composition, morphological and physicochemical performances at relatively high loading ratios of the used micro- and nanofillers. It is already used in the fabrication of materials with conferred optical properties, thermal conductivity, heat resistance, flame retardancy, biocompatibility by the incorporation of aluminum powder [13], carbon nanofibers [14], nanosilica [15], clay [16], glass beads [17], and hydroxyapatite [18]. Mechanical downsizing of TR waste is a process often applied to granulate the tire waste to the called ground rubber tire, which can be further devulcanized to become reclaimed tire rubber powder, making it suitable for blending with different polymer matrices [19]. In this aspect, smaller rubber particles are preferable, offering the possibility to obtain better dispersions within the polymer material. In addition, the greater surface area of smaller particles offers the possibility to enhance the interface adhesion between the rubber domains and the polymer matrix for decreased phase separation effect. In the literature, it was found that rubber particles sized under 500 \(\upmu\)m allow the fabrication of materials with acceptable balance in terms of mechanical properties based on PP [20], high density polyethylene (HDPE) [21], and ethylene vinyl acetate copolymer (EVA) [22]polymers. An improvement in the material impact strength (about 20%) was also obtained after incorporation of particles with an average size of 420 \(\upmu\)m in PP thermoplastic blends, in contrast to materials containing 1.2 and 2.4 mm sized ones [23]. In the present study, we proposed a one-step approach for the fabrication of TR waste-loaded polymer composites by 3D printing using SLS. For this purpose, two kinds of polymer matrices were used: polyamide (PA12) and thermoplastic urethane (TPU) for their rigid and elastomeric properties, respectively. The TR particles morphology and composition were first evaluated, as well as their dispersion ability at different amounts (10, 15, 30, and 40 wt%) within the printed device volume. Special attention was paid to the material thermal stability and mechanical properties (tensile and impact tests) and the surface resolution as a part of the quality validation procedure. As a final touch, different prototypes were proposed paving the way to new horizons in the TR waste reuse and valorization as a solution for the prolongated half-life of the rubber waste.