Development and characterization of sustainable hybrid composites: Recycled HDPE modified with wood powder and calcium carbonate

This study investigated the development and characterization of hybrid bio-filled composites based on recycled high-density polyethylene (HDPE) reinforced with wood powder and calcium carbonate. A systematic experimental design was employed wherein wood powder content was varied from 0 to 20 wt% (designated W0, W5, W10, W15, and W20) whilst maintaining constant levels of calcium carbonate (10 wt%) and maleic anhydride-grafted polypropylene (MAPP) compatibiliser (6 wt%) across all formulations. This approach enabled clear identification of how wood powder specifically influenced the composite’s characteristics. Mechanical, and thermal characterization revealed substantial property enhancements attributable to lignocellulosic reinforcement incorporation. Tensile stiffness and modulus exhibited monotonic increases throughout the compositional range, with the W20 formulation achieving approximately 56% enhancement in both properties (685,000 N/m and 1195 MPa respectively) compared to the wood-free W0 baseline (440,000 N/m and 765 MPa) formulation. Tensile strength displayed optimal performance at 15 wt% wood powder loading (24.6 MPa), representing a 5% improvement over the baseline (23.4 MPa), with marginal decline observed at 20 wt% loading due to particle agglomeration effects. Elongation at break decreased substantially from 37.5% for W0 to 7.5% for W20, reflecting the transition from ductile to brittle-like mechanical behaviour characteristic of rigid particle-reinforced systems. FTIR spectroscopy confirmed characteristic functional groups in all composite constituents and provided evidence of interfacial interactions between MAPP and wood powder through formation of ester linkages, though substantial unreacted hydroxyl groups persisted in all formulations. Differential scanning calorimetry revealed that wood powder acted as a heterogeneous nucleating agent, producing modest increases in HDPE melting temperature and systematic broadening of melting endotherms with increasing filler content. Thermogravimetric analysis demonstrated multi-stage degradation profiles in wood-containing composites, with degradation onset temperature decreasing systematically from approximately 420°C for W0 to 300°C for W20, though all formulations retained sufficient thermal stability for practical processing and application. The results demonstrate that hybrid bio-filled composites incorporating recycled HDPE, wood powder, and calcium carbonate represent viable sustainable materials offering substantial stiffness and modulus enhancements with acceptable trade-offs in ductility and thermal stability.