Sustainable 3D printed PLA composite using sword bean micro fiber and Teff straw–derived biosilica

This study focuses on the development and characterization of sustainable 3D-printed PLA-based composites reinforced with silane-treated sword bean micro fibers and silane-treated Teff-straw–derived biosilica. The composites were fabricated at a 100% infill ratio to ensure a dense structure with minimal porosity and improved inter-raster bonding. The mechanical, thermal, and moisture-resistance properties were systematically evaluated to assess the synergistic reinforcement effect of the dual fillers. The mechanical results revealed a significant improvement in strength and toughness with the addition of reinforcements compared to neat PLA. Among all specimens, PFB2 exhibited the best mechanical performance, achieving a tensile strength of 130 MPa, flexural strength of 141 MPa, impact energy of 4.8 J, and hardness of 82 Shore D, marking increases of 124%, 99%, 1016%, and 6.5%, respectively, compared to neat PLA (P). These enhancements were attributed to the strong interfacial bonding facilitated by silane treatment, uniform dispersion of the reinforcements, and the dense microstructure achieved through full infill printing, which ensured continuous load pathways and efficient stress transfer. In contrast, PFB3 demonstrated the best performance in functional properties, with the highest thermal conductivity of 0.51 W/m·K (a 45.7% increase over PLA) and the lowest water absorption of 1.51% (a 21.4% reduction), due to the formation of interconnected thermally conductive networks and the reduced permeability of the matrix by well-distributed biosilica particles. The SEM microstructural analysis confirmed strong fiber–matrix interfacial adhesion, fiber breakage rather than pull-out, and uniform filler dispersion, all of which contributed to the improved mechanical and thermal behavior. Overall, the results confirm that the silane-treated sword bean fiber and Teff-straw biosilica hybrid system effectively enhances the mechanical strength, thermal conductivity, and moisture resistance of PLA composites, positioning PFB2 as the optimum formulation for structural performance and PFB3 for functional property enhancement in sustainable additive manufacturing applications.