Particle Analysis and Mechanical–Thermal Properties of Bio‐Derived and Commercial CaCO 3 Reinforced Laboratory‐Reprocessed Polypropylene Composites

This study investigates laboratory‐reprocessed polypropylene (rPP)‐based composites reinforced with calcium carbonate (CaCO 3 ) derived from orange peel as potential alternatives to traditional CaCO 3 ‐based composites. Bio‐derived CaCO 3 was synthesized from orange peel waste via a green route and incorporated into a model rPP matrix. Composites containing bio‐derived and commercial CaCO 3 were prepared at low loadings (1, 2, and 3 wt%) with 4 wt% PP‐g‐MAH using twin‐screw extrusion and injection molding. The obtained rPP/CaCO 3 composites were tested for rheological, mechanical, thermal, and morphological properties. At 3 wt%, bio‐derived CaCO 3 composites exhibited higher tensile modulus retention (1890 MPa vs. 1780 MPa), stress at break (37.0 MPa vs. 34.9 MPa), and impact strength (47.58 kJ/m 2 vs. 44.91 kJ/m 2 ) than the corresponding commercial CaCO 3 composites, although the tensile modulus remained slightly lower than that of neat laboratory‐reprocessed polypropylene. Thermal studies indicated improved degradation resistance relative to the unfilled matrix, while microscopy revealed a more uniform distribution of bio‐derived CaCO 3 particles. The finer particle size distribution of the bio‐derived CaCO 3 (4–13 μm), compared with commercial CaCO 3 (10–142 μm), promoted improved dispersion and filler–matrix interaction. These results indicate that orange‐peel‐derived CaCO 3 is a promising sustainable alternative to conventional mineral fillers for laboratory‐reprocessed polypropylene composites.