Development and characterization of sustainable PKS/CaCO ₃ /HDPE hybrid composites for enhanced thermal and mechanical performance

This study presents a comprehensive evaluation of hybrid composites made from high-density polyethylene (HDPE), calcium carbonate (CaCO 3 ), and palm kernel shell (PKS) particles, focusing on their thermal, mechanical, and moisture-resistance properties. PKS, a lignocellulosic agro-waste, was pretreated with NaOH and incorporated at varying loadings (10–25 wt%) and particle sizes (125 µm and 500 µm); CaCO 3 content was adjusted so that the total filler loading remained 30 wt%. Fourier-transform infrared spectroscopy (FTIR) confirmed chemical interactions and surface modification of PKS after treatment. Differential Scanning Calorimetry (DSC) revealed minimal variation in melting temperature across formulations but showed distinct changes in enthalpy of fusion and degree of crystallinity, particularly with increasing PKS content. Thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) indicated enhanced thermal stability for CaCO 3 -rich composites, while PKS-rich formulations showed earlier onset of thermal degradation due to lignocellulosic decomposition. Water absorption results demonstrated that both filler content and particle size significantly influence hydrophilicity, with smaller particles exhibiting reduced water uptake because of better dispersion and packing. Mechanical testing showed that composites with 10 wt% PKS (especially at 125 µm) exhibited superior ultimate tensile strength and impact energy, balancing reinforcement and toughness. Higher PKS contents led to agglomeration, reduced ductility, and diminished strength. Hardness generally increased with filler content and was more pronounced in composites containing larger PKS particles. The results highlight the potential of PKS/CaCO 3 /HDPE hybrids as sustainable, high-performance materials for engineering applications, with optimal performance achieved at 10–15 wt% PKS using fine particles.