Effect of biochar reinforcement on thermal and mechanical properties of epoxy composites

The integration of sustainable waste-derived reinforcements into polymer composites is an effective strategy for improving performance while reducing environmental impact. In this study, rice husk biochar was investigated as a particulate reinforcement for epoxy composites, and its influence on mechanical, tribological, and thermal behaviour was systematically evaluated. Epoxy composites containing different weight fractions of rice husk biochar were fabricated and characterised. Tensile strength increased from 22.7 MPa for neat epoxy to 29.2 MPa at 9 wt.% biochar, accompanied by an increase in elongation at break from 0.8% to 1.31%, indicating improved stress transfer and reduced brittleness. Flexural strength similarly improved from 58 MPa to 70.1 MPa, confirming enhanced resistance to bending-induced failure. Fracture-surface analysis revealed suppression of cleavage-dominated river patterns and increased crack deflection in biochar-reinforced composites. Dry sliding wear analysis showed that intermediate biochar content increased wear mass loss (0.76 mg at 6 wt.%) due to particle pull-out and third-body abrasion, whereas higher filler loading promoted more stable surface interaction. Thermogravimetric analysis demonstrated improved thermal stability of biochar-reinforced epoxy composites at elevated temperatures, particularly in the 400 °C–550 °C range, attributed to char-mediated thermal shielding. Overall, the results demonstrate that rice husk biochar provides multifunctional enhancement of epoxy composites by improving mechanical performance and high-temperature thermal resistance, while introducing content-dependent tribological effects, highlighting its potential as a sustainable reinforcement for epoxy-based non-load bearing structural applications.