Synergistic effect of Silicon Nitride nanoparticles and Hemp/Basalt hybrid reinforcement on mechanical integrity and fracture resistance of epoxy composites

Polymer composites have been a subject of extensive research for lightweight, high strength and environmentally friendly applications for advanced structures and engineering. This research aims at exploring the synergistic effect of silicon nitride (Si₃N₄) nanoparticles and alkali-/silane-treated hemp/basalt (H/B) hybrid reinforcements on mechanical properties, interfacial adhesion and fracture resistance of epoxy (Ep) composites. The hemp fibers were alkali-treated with NaOH, the basalt fibers were silane-treated, and the Si₃N₄ nanoparticles were added up to 2 wt.%. The surface modification on the fiber and uniform dispersion of nanoparticles had a significant effect on improving the structural integrity of the composites. The composite having 1.5 wt.% Si₃N₄ showed the highest interlaminar shear strength of 27.77 MPa (70.9% higher) and flexural strength of 258.91 MPa (42% higher) than the H/B F-Ep composite without Si₃N₄. The maximum fracture toughness (2.6828 ) was obtained at 1 wt.% Si₃N₄, which is a 57.3% increase because of crack pinning, crack deflection and crack bridging. However, 2 wt.% Si₃N₄ led to the agglomeration of the nanoparticles and to localized stress concentrations, which slightly lowered the mechanical performance. The results show that the optimized incorporation of Si₃N₄, together with the chemically modified H/B hybrid reinforcements, is a promising approach for the enhancement of damage tolerance of the epoxy nanocomposites for lightweight structural applications in the automotive and aerospace sectors.