Polymer nanoparticle composites present industrial potential in many applications. However, some limitations for the application of these composites are due to the non-uniformity of their mechanical properties. One of the main issues of that drawback is the lack of uniform distribution of the nanoparticle's reinforcement inside the polymer matrix. In other words, uniform distribution of nanoparticles throughout polymer matrices presents a crucial issue for obtaining sound parts with fair enough mechanical properties. That would present a limitation for use in different areas of application. A mechanical mixer with a special design has been developed during the present work. A prototype mixer has been carried out, and used for the synthetization of polystyrene carbon nanoparticles, (CNP's) composites. The design of the developed mechanical mixer is based on the principle of subjecting the mixture of CNP's and polymers to multi-shearing strokes in a bi-direction extrusion die during heating at an appropriate temperature for a specific time. The produced composites have been subjected to SEM examination, and mechanical testing to investigate the effectiveness of using the developed mechanical mixture. SEM examination has shown a fair enough distribution of the carbon nanoparticles throughout the polymer matrix. The mechanical properties of the produced composites have been evaluated, and the results showed comparable values with respect to those dismantled in publications.