The global challenges of plastic waste and fly ash accumulation demand innovative recycling solutions. In Malaysia, the consumption of 11.2 million tonnes of coal annually generates approximately 2 million tonnes of fly ash, while the recycling of Polypropylene (PP) is hindered by thermo-oxidative and shear-induced degradation during mechanical recycling, resulting in reduced mechanical properties. This study addresses these issues by fabricating recycled PP composites incorporating varying fly ash contents, using a single cycle of mechanical recycling with extrusion and injection moulding methods. The composites were comprehensively tested for tensile, flexural, and compressive strengths, as well as microstructural behaviour. The results reveal a complex relationship between fly ash content and mechanical performance: while tensile strength decreases with increasing fly ash, flexural strength and strain peak at 5 % and 9 % fly ash, respectively. Compressive strength also shows a slight increase up to 7 % fly ash, indicating an optimal range for enhancing mechanical performance. Furthermore, mathematical models were proposed to predict the mechanical properties of rPP – fly ash composites, providing a valuable tool for future material design. These findings demonstrate that optimization of fly ash content can mitigate the effects of polymer degradation, offering a sustainable solution to improving the mechanical performance of this composite.