Fused deposition modelling of hemp hurd and cocoa pod husk biocarbon-reinforced PLA biocomposites

This study investigates the mechanical, tribological, flammability, and thermal performance of polymer composites reinforced with 30 vol.% hemp hurd microfibers and filled with 1–5 vol.% cocoa pod husk–derived biocarbon, with and without silane surface treatment. Untreated (PHU) and silane-treated (PHT) composites were compared with neat polymer (P) and fiber-only composite (PH). The novelty lies in the synergistic combination of hemp hurd microfibers and silane-treated biocarbon to enhance multifunctional properties of sustainable composites. Reinforcement with hemp fibers increased tensile and flexural strengths from 59 MPa to 73 MPa (P) to 109 MPa and 118 MPa (PH), representing improvements of 84.7% and 61.6%, respectively. Among all formulations, PHT1 (3 vol.% treated biocarbon) exhibited the highest tensile (138 MPa) and flexural strengths (156 MPa), corresponding to enhancements of 133.9% and 113.7% over neat polymer. Tribological performance also improved significantly; PHT2 (5 vol.% treated biocarbon) achieved the lowest wear rate (0.0182 mm 3 /Nm) and coefficient of friction (0.235), with reductions of 48.4% and 42.3%, respectively. Flammability resistance improved markedly, as flame propagation decreased from 13.4 mm/s (P) to 5.6 mm/s (PHT2), achieving a 58.2% reduction while maintaining a UL-94 V-0 rating. Thermogravimetric analysis showed enhanced thermal stability, with decomposition temperature increasing from 231°C to 284°C (22.9% improvement). SEM analysis revealed improved interfacial bonding in treated composites, while untreated samples showed agglomeration and voids. Overall, silane-treated biocarbon significantly enhances composite performance, indicating strong potential for sustainable structural applications.