Characterization of vinyl ester composites reinforced with surface modified tecomastans stem fiber and kodo millet husk biochar

Abstract

This study investigated the characterization of vinyl ester composites reinforced with Tecomastans stem fiber and Kodomillet husk biochar, with and without silane treatment. Mechanical, wear, thermal, and surface wettability properties were systematically evaluated alongside SEM microstructural analysis. The results demonstrated that the incorporation of 40 vol.% fiber significantly improved the mechanical performance of the brittle vinyl ester resin, and the addition of biochar particle further enhanced load distribution, crack resistance, and interfacial compatibility. Silane treatment consistently improved performance across all test categories compared to untreated composites, owing to enhanced fiber–matrix and filler–matrix adhesion. The optimum balance of mechanical properties is obtained in specimen VTS1 with 2 vol.% of silane-treated biocharfiller, which exhibited tensile strength of 150 MPa, flexural strength of 160 MPa, impact energy of 5.46 J, and hardness of 84 Shore D. These values represent significant improvements due to efficient stress transfer, crack pinning, and reduced fiber pull-out enabled by silane coupling. For wear, thermal, and surface properties, specimen VTS2 with 4 vol.% of silane-treated biocharfiller showed superior performance with a minimum wear rate of 0.016 mm³/Nm, the lowest COF of 0.22, highest thermal conductivity of 0.46 W/mk, and the maximum water contact angle of 79°. These results are attributed to the combined effects of higher filler loading, strong silane-induced adhesion, reduced interfacial resistance, and micro/nano-scale surface roughness that promoted stable tribofilms, efficient phonon transport, and enhanced hydrophobicity. SEM analysis provided supporting evidence, where untreated resin surfaces appeared smooth and featureless, whereas treated specimens revealed rough fiber surfaces, improved filler anchoring, and better matrix–reinforcement integration, validating the improvements in bulk properties. Overall, the results confirm that silane treatment plays a pivotal role in maximizing reinforcement efficiency, with VTS1 excelling in mechanical performance and VTS2 demonstrating superior wear, thermal, and surface resistance properties.