Study on the characterization of polyester composites reinforced with natural VignaRadiata fiber and silicon nitride from foxtail millet husk

Increasing pressure on conventional construction materials has accelerated the search for sustainable alternative to steel reinforcement. This study develop bio-based fiber-reinforced polymer (FRP) rebars incorporating acid-silane treated Vignaradiata stalk fibers and silicon nitride (Si 3 N 4 ) particles derived from foxtail millet husk, with the objective of enhancing interfacial adhesion and structural performance. The rebars were fabricated using a hand lay-up process and evaluated in accordance with ASTM standards. The composite containing 40 wt. % treated fiber and a 2 wt. % Si 3 N 4 (MBS3) demonstrated the best overall mechanical performance, with tensile, flexural, and compressive strengths of 122 MPa, 168 MPa, and 130 MPa, respectively. Increasing the filler loading 4 wt. % (MBS4) led to improvements in hardness (79 Shore-D) and moisture resistance, with water absorption reduced to 0.258%, although a decline in strengths was observed relative to MBS3. Structural evaluation through three-point bending test of reinforced concrete beams indicated that MBS3 achieved superior performance, exhibiting a bending strength of 116 Mpa, a peak load of 98 kN, and a lower deflection of 12 mm, reflecting enhanced stiffness and load-bearing efficiency. In addition, it was exhibited the highest thermal conductivity values of 0.392 W/mK. Microstructural analysis confirmed that the combined acid and silane treatment significantly improved fiber-matrix bonding, while promoting dispersion of Si 3 N 4 particles. These results highlight that acid-silane treated natural fiber-based FRP rebars present a viable and sustainable alternative to traditional steel reinforcement, offering a balanced combination of mechanical strength, durability, and reduced environmental impact.