Chemical and structural characterization of ramie-based epoxy composites reinforced with macadamia nut shell biochar

This study examined the effect of biochar by macadamia nut shell waste on the mechanical behaviour of ramie fibre reinforced epoxy composite. Controlled pyrolysis was used to prepare biochar at 350 °C, followed by ball milling to produce a mesoporous carbon structure with a crystallinity index of 40.5%, a crystallite size of 1.6 nm, a Brunauer-Emmett-Teller (BET) surface area of 326 m²/g and an average pore size of 3.8 nm. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) analyses confirmed partial graphitization and the presence of oxygen-containing functional groups, while surface roughness analysis (R_a = 0.2382 µm, R_q = 0.2985 µm) and particle size measurements (7.40 ± 1.92 µm, standard deviation = 1.08 µm) indicated a highly textured morphology with a good dispersion potential. Ramie-epoxy composites with varying biochar loadings (1, 3, and 5 wt%) were fabricated using hand lay-up followed by compression molding. Mechanical testing showed that incorporation of 3 wt% biochar (MR3) showed high improvement in tensile strength by 47.45 MPa (33%), flexural strength by 68.46 MPa (18%), and impact resistance by 3.9 kJ/mm² (50%) than 1 wt% composite (MR1). These enhancements were attributed to the better interfacial bonding, uniform dispersion of filler and efficient stress transfer. These enhancements were attributed to the improved interfacial bonding, uniform filler dispersion, and efficient stress transfer. Beyond 3 wt% biochar loading, marginal reductions in mechanical properties were observed due to particle agglomeration and void formation. This study demonstrates the effective valorization of macadamia nutshell waste into high-performance, eco-efficient hybrid composites, with potential applications in lightweight structural, automotive, and green engineering systems.