Biochar from cashew nut shells: A sustainable reinforcement for enhanced mechanical performance in hemp fibre composites

The pursuit of sustainable and eco-friendly materials has fuelled research into enhancing composite materials using bio fillers derived from renewable sources. This study investigates the incorporation of bio filler - biochar produced from cashew nut shell, in hemp fibre composite to achieve a balance between performance and environmental sustainability. Hemp fibre composites were fabricated with four different weight percentages of biochar such as 5, 10, 15, and 20 wt%. Hemp fibre composites with biochar showed enhanced mechanical strength and water resistance when compared to composite without biochar. The composites containing 10 wt% biochar added showed the maximum tensile, impact, and hardness, ca. 94%, ca. 38%, and ca. 7% increase compared to composite without biochar, respectively. The highest flexural strength (ca. 71 MPa) was observed at a biochar addition of 15 wt%. The integration of biochar improved the filler-matrix interaction by enhancing adhesion, creating effective stress transfer within the vinyl ester matrix, thereby reinforcing the composite's structural integrity. In the water absorption test, the biochar acted as barrier to the water molecules and reduced the water absorption by ca. 32–63%. These findings highlight the potential of biochar-based fillers in advancing the field of composite materials, providing a more nuanced understanding of their applications in addressing both environmental concerns and bio waste accumulation.