Optimization and thermo-mechanical characterization of hybrid natural–synthetic fiber polymer composites with organic fillers

This study presents a novel hybrid polymer composite reinforced with carbon, basalt, and KMnO 4 -treated hemp fibers, further enhanced with dual organic fillers—calcium carbonate (CaCO 3 ) and coconut shell powder (CSF). Unlike previous studies, this work uniquely combines chemically treated natural fibers with synthetic reinforcements and dual fillers, optimized using Taguchi’s L9 orthogonal array and regression modeling. The optimized configuration of 15 wt.% treated hemp fiber, 74 wt.% epoxy concentration, and carbon–basalt hybrid reinforcement exhibited superior mechanical properties, including a tensile strength of 132.56 MPa, flexural strength of 353.77 MPa, hardness of 78 Shore D, and impact energy of 7.5 kJ/m 2 . Thermal stability was significantly improved, with major degradation temperatures exceeding 383°C, as confirmed by TGA/DTG analysis. Regression models showed strong predictive accuracy, validated through residual analysis. The synergistic effect of hybrid reinforcement and optimized filler loading led to a dense, thermally stable matrix with enhanced mechanical integrity, making these composites highly suitable for applications in automotive, aerospace, and structural engineering sectors.