Effect of Nano-Silica on the Mechanical, Thermal and Microstructural Properties of Areca–Hemp Epoxy Hybrid Composites

Natural-fiber-based composite materials are gaining popularity because they are lightweight, renewable, and more sustainable than existing synthetic fiber composites, offering numerous benefits for structural engineering applications. However, the lack of adhesion at natural-fiber–matrix interfaces due to the non-polar hydrophobic nature of the fibers and hydrophobic epoxy matrices produces gaps due to void formation during manufacturing. Also, the non-uniform distribution of natural fibers and the reinforcement make the composite perform inefficiently, prone to brittleness, have lower temperature resistance and lack proper bonding between fibers. The present research work aimed to achieve the maximum flexural, tensile, compressive strength, thermal resistance and toughness of areca–hemp hybrid epoxy composites with nano-silica (AHNS) at varying percentages (1 wt%, 2 wt%, 3 wt%, and 4 wt%) as reinforcement. The results showed that AHNS-2 with 2 wt% of nano-silica yielded superior flexural and compression strength and Shore-D hardness (64.40 N/mm2, 57.46 N/mm2 and 83, respectively); AHNS-4 with 4 wt% nano-silica exhibited the best performance in terms of tensile strength, toughness and maximum degradation-rate temperature (61.90 N/mm2, 81.99 J/m and 377.4 °C, respectively). The SEM morphology analysis revealed fiber pull-out, matrix cracks, fiber breakage, and fiber–matrix interfacial characteristics. These microstructural features showed a considerable impact on the mechanical properties of the composites, especially on density, hardness, strength and toughness. The elemental analysis revealed that carbon (64.92%) and oxygen (33.08%) were the predominant elements present, although silicon (2%) was also present in AHNS-2. The presence of silicon provided evidence of the localized incorporation of nano-silica within the epoxy matrix. It was observed that the mechanical properties of AHNS with 1–4 wt% nano-silica were significantly better compared to the unfilled composite (AHNS-0 wt% nano-silica).