Influence of post-consumer recycled polypropylene on the mechanical performance of glass fiber-reinforced polypropylene

Glass fiber-reinforced polypropylene (GFR-PP) is widely used for its excellent mechanical properties and low weight. However, sustainability concerns arise due to its reliance on virgin polymers and the difficulty of incorporating post-consumer recycled polypropylene (PCR-PP). This study investigates the effect of increasing PCR-PP content in GFR-PP composites. Particular attention is given to titanium dioxide (TiO 2 ), a common pigment in white polypropylene products that remains in post-consumer streams and becomes a contaminant in glass-fiber-reinforced compounds. To isolate its role, reference compounds were produced using virgin polypropylene with controlled additions of TiO 2 . Results reveal that TiO 2 is the primary driver of tensile performance loss due to its high hardness and sharp-edged particle morphology, which induce abrasive wear on the glass fibers during high-shear melt processing. This abrasive interaction caused a 22% reduction in average fiber length even at low concentrations (0.1–0.2 wt%), directly decreasing tensile strength from 77 MPa to 63 MPa. In contrast, impact strength declined progressively from 15.2 to 8.2 kJ/m 2 as recycled content reached 70%, indicating degradation mechanisms driven by matrix heterogeneity and incompatible polymer inclusions. These findings demonstrate that TiO 2 contamination governs fiber breakage and tensile loss, while matrix heterogeneity primarily controls impact resistance. By isolating these contributions, this study provides critical insights into mechanical property loss mechanisms in GFR-PP with rPP and highlights the need for improved sorting and filtration practices to enable higher recycled content in structural applications.