Sustainable Polypropylene Blends: Balancing Recycled Content with Processability and Performance

The increasing demand for sustainable materials has renewed interest in recycling polyolefins, particularly polypropylene (PP), due to its widespread use and environmental persistence. Post-consumer recycled polypropylene (PP_r), however, often exhibits compromised properties from prior exposure to thermal, oxidative, and mechanical degradation. This study investigates the potential of using post-consumer PP_r in melt-blended extrusion formulations with virgin PP (PP_v), focusing on how different PP_r contents affect processability, thermal stability, oxidative resistance, and mechanical performance. Blends containing 25%, 50%, and 75% PP_r, as well as 100% PP_r and virgin PP, were evaluated using melt flow index (MFI), differential scanning calorimetry (DSC), oxidation induction time (OIT), thermogravimetric analysis (TGA), and tensile testing. Results show that increasing PP_r content improves polymer fluidity and thermal stability under inert conditions but significantly reduces oxidation resistance and ductility. However, the 25% PP_r blend demonstrated a favourable balance between performance and recyclability, presenting 96% of the elastic modulus and 101% of the yield strength of PP_v. Homogenization by extrusion improved the oxidative stability of recycled PP by 22% compared to its non-extruded form. These findings support the use of low-to-moderate levels of PP_r in virgin PP for applications requiring predictable and tunable performance. contributing to circular economy goals.