Oxidation of polyolefins by ultraviolet/visible irradiation is a significant limitation for their use in several technological applications. The use of high-tech additives such as silicon microparticles becomes a compositing strategy that can improve the performance of these materials at long-term service conditions. Silicon particles were added to non-additivated raw polypropylene (PP) prepared by hot melt extrusion and subjected to accelerated sunlight irradiation tests. The stability of thermal properties, mechanical performance and thermal decomposition behaviour of composites was evaluated by differential scanning calorimetry, dynamic mechanical-thermal analysis and thermogravimetry. This paper shows the potential of silicon microparticles to protect PP from degradation during both processing and accelerated sunlight irradiation. The addition of polydisperse silicon microparticles to the raw polypropylene preserved the appearance and improved the thermal behaviour, mechanical properties and thermal stability. It was found that silicon particles at 5 wt% provided a suitable protection of raw non-additivated PP against sunlight irradiation.