This study investigates the use of waste marble dust (MD) as a reinforcing material in recycled polyethylene terephthalate (rPET) composites to create environmentally friendly materials. The composites were fabricated using extrusion and injection molding, with MD content ranging from 0 to 20 wt%. Characterization techniques including FTIR, DSC, TGA, and DMA were employed to analyze the structural and thermal properties of the composites. Key findings include: - FTIR analysis confirmed no alteration in the molecular structure of the components. - DSC revealed that MD particles acted as nucleating agents, shifting the crystallization temperature from 196.7 °C to approximately 204.4 °C. However, the presence of MD also reduced the mobility of chain molecules, leading to a decrease in the crystallinity ratio from 23.7% to 19.2%. - TGA measurements showed a slight increase in the thermal stability of rPET, with the decomposition temperature increasing from 446 °C to 451 °C when 20 wt% MD was incorporated. - DMA measurements indicated an improved storage modulus in the entire temperature range for MD-filled composites compared to neat rPET. Several factors derived from DMA data, including the effectiveness factor, degree of entanglement, and reinforcing efficiency factor, suggested a decent interaction between the components, indicating proper reinforcing ability of marble powder. - Above 5 wt% MD content, the reinforcing efficiency deteriorated due to the agglomeration of filler particles, as observed through SEM images. The study concludes that while MD can enhance the mechanical and thermal properties of rPET composites up to 5 wt% content, higher concentrations lead to mechanical degradation due to filler agglomeration.This study investigates the use of waste marble dust (MD) as a reinforcing material in recycled polyethylene terephthalate (rPET) composites to create environmentally friendly materials. The composites were fabricated using extrusion and injection molding, with MD content ranging from 0 to 20 wt%. Characterization techniques including FTIR, DSC, TGA, and DMA were employed to analyze the structural and thermal properties of the composites. Key findings include: - FTIR analysis confirmed no alteration in the molecular structure of the components. - DSC revealed that MD particles acted as nucleating agents, shifting the crystallization temperature from 196.7 °C to approximately 204.4 °C. However, the presence of MD also reduced the mobility of chain molecules, leading to a decrease in the crystallinity ratio from 23.7% to 19.2%. - TGA measurements showed a slight increase in the thermal stability of rPET, with the decomposition temperature increasing from 446 °C to 451 °C when 20 wt% MD was incorporated. - DMA measurements indicated an improved storage modulus in the entire temperature range for MD-filled composites compared to neat rPET. Several factors derived from DMA data, including the effectiveness factor, degree of entanglement, and reinforcing efficiency factor, suggested a decent interaction between the components, indicating proper reinforcing ability of marble powder. - Above 5 wt% MD content, the reinforcing efficiency deteriorated due to the agglomeration of filler particles, as observed through SEM images. The study concludes that while MD can enhance the mechanical and thermal properties of rPET composites up to 5 wt% content, higher concentrations lead to mechanical degradation due to filler agglomeration.