Effect of aging conditions on surface-modified biochar and nutmeg short fiber-reinforced polyester composite: properties and performance

This study investigates the mechanical, thermal, and physical performance of polyester composites reinforced with silane-treated nutmeg short fiber and watermelon rind biochar, aged for 60 days at 40°C. The results reveal that composite P3, containing 2 vol.% biochar, achieved the highest mechanical strength, with a tensile strength of 63.9 MPa, flexural strength of 109.1 MPa, and compression strength of 82.7 MPa, attributed to optimal biochar dispersion enhancing fiber-matrix interaction and load transfer. In contrast, P5, with 8 vol.% biochar, exhibited the lowest density (0.82 kg/m3) and highest porosity (0.92%), yet demonstrated the highest thermal conductivity (0.66 W/mK) and minimal water absorption (0.003%), reflecting the formation of conductive networks and superior moisture resistance. SEM analysis highlighted fracture mechanisms, showing fiber breakage in P1, fiber pull-out in P2, and well-dispersed biochar in P4, while P5 exhibited river patterns indicative of enhanced crack propagation resistance. Minimal property degradation after aging confirms the effectiveness of silane treatment in improving interfacial adhesion and limiting moisture-induced deterioration. Overall, P3 is optimal for mechanical applications, whereas P5 offers superior thermal and physical performance, positioning these biochar-fiber composites as sustainable alternatives for multifunctional structural and thermal applications.