Toward Greener Hybrid Composites: Effect of Wood Powder and Calcium Carbonate on Recycled <scp>HDPE</scp> With Tyre and <scp>MAPE</scp> Modifiers

ABSTRACT The growing demand for environmentally responsible materials has accelerated research into green composites that utilize recycled polymers and waste‐derived fillers. However, balancing mechanical strength, thermal stability, and compatibility among multiple fillers remains a key challenge. This study addresses this by formulating recycled high‐density polyethylene (rHDPE) composites reinforced with wood powder (WP) and calcium carbonate (CaCO 3 ), and modified with ground tyre powder (GTP) and maleic anhydride grafted polyethylene (MAPE). The wood powder serves as a renewable lignocellulosic reinforcement to improve stiffness and reduce material cost, while calcium carbonate acts as an inorganic filler enhancing thermal stability and rigidity. Ground tyre powder is incorporated primarily as a waste valorization strategy to address the environmental challenge of end‐of‐life tyres. MAPE (5 wt%) functions as a compatibilizer to strengthen interfacial bonding between the hydrophilic and hydrophobic phases. Composites containing 0–25 wt% WP were prepared with fixed levels of CaCO 3 (5 wt%), GTP (5 wt%), and MAPE (5 wt%) via extrusion and injection molding. The 0 wt% WP formulation serves as an internal baseline (rHDPE +5% MAPE +5% CaCO 3 + 5% GTP), not neat rHDPE. Mechanical testing revealed marked increases in tensile strength, stiffness, and modulus with higher WP content, with optimal performance at 25 wt% WP. Elongation at break decreased accordingly, indicating the expected stiffness–ductility trade‐off. Thermogravimetric analysis (TGA) demonstrated notable improvements in char yield attributed to the cumulative contributions of CaCO 3 and tyre‐derived residues, while differential scanning calorimetry (DSC) indicated reduced crystallinity. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of constituent materials and showed spectral features consistent with enhanced interfacial compatibility, although covalent bond formation could not be definitively confirmed without complementary techniques (e.g., XPS). The findings demonstrate that combining lignocellulosic and inorganic fillers with recycled polymers and waste rubber yields composites with superior rigidity, strength, and thermal stability. This work provides a foundational formulation and processing protocol for sustainable composite development, while explicitly acknowledging that mechanistic interpretations of interfacial chemistry and filler synergy require further validation through controlled experimental designs and direct morphological/spectroscopic evidence.