**6. Conclusions and Future Developments**

The addition of IF/INTs has been demonstrated to be a very efficient strategy to improve the thermal, mechanical and tribological properties of thermoplastic polymers like iPP, PPS, or PEEK and their fiber-reinforced composites. These materials can be fabricated by simple melt-processing and compression molding without the need for modifiers or surfactants, leading to a very homogenous dispersion of the nanofillers within the matrix. More importantly, they exhibit similar or enhanced performance when compared with composites that incorporate CNTs, nanoclays or other inorganic spherical nanoparticles, but are substantially more cost-effective, efficient and environmentally-friendly. Results demonstrate the existence of synergistic effects of both micro-and nanoscale fillers on enhancing the stiffness, strength, thermal conductivity, thermal stability, flammability, and wear resistance of hierarchical thermoplastic-based composites. This new family of materials has a wide range of potential applications ranging from medicine to the aerospace, automotive, and electronics industries. Some of these applications are still at an early stage of research and development. However, for optimal control of the properties of these new materials, it is highly important to tailor the fabrication process from the viewpoint of the final product. In particular, the improvement and application of these nanocomposites in comparison with other organic-inorganic hybrid nanomaterials (silica, metal oxides, clays, *etc*.) depend on how effectively we optimize and scale-up

their fabrication method. For specific applications, these nanoparticles should be surface functionalized in order to confer more selectivity, specificity and reactivity with the polymer chains. An additional demanding area is the potential of these nanoparticles in the field of biocompatible and/or biodegradable polymeric composites for packaging and medical applications and their eventual toxicological effects, if any, need to be investigated. Research and progress in these areas will not only benefit the current applications but would also lead to new markets as well as to future development of diverse hierarchical thermoplastic-based composites.
