Effects of Polypropylene on the Mechanical and Physical Properties of Recycled HDPE Composites with 20% CaCO3

This study aims to optimize the mechanical and thermal properties of a composite composed of recycled high-density polyethylene (HDPE), 20% by mass of calcium carbonate (CaCO3), and polypropylene (PP) in varying proportions (0%, 10%, 25%, and 30%). Corrugated pipes with internal diameter of 300 mm were manufactured through a single-step dual-wall extrusion process and subsequently characterized to identify the optimal formulation. The results showed that incorporating 30% PP increases the melt flow index (MFI) by 5.6%, indicating a slight decrease in viscosity. Despite this, the material retains good mechanical properties, likely due to improved phase interaction and optimized filler dispersion. Additionally, the density decreases by 15%, enhancing the material’s flexibility. The oxidation induction time (OIT) analysis reveals satisfactory thermal stability with an oxidation time of 40 min, despite a 48% reduction compared with the PP-free blend. Mechanically, ring stiffness increases by 62%, reaching 10.5 kN/m2, and the elastic modulus rises by 500 MPa. These results suggest that the R-HDPE/30% PP/20% CaCO3 composite offers an optimal balance among rigidity, flexibility, and durability. It enhances the performance of recycled materials, reduces pipe weight and cost, and is well-suited for demanding industrial applications, particularly for wastewater and stormwater drainage. This research provides an innovative solution for the valorization of plastic waste.