High-performance biocomposites: leveraging lotus fiber and waste Kigelia pinnata fruit shell biochar for enhanced mechanical and fire-retardant properties

The use of naturally derived biomass-based material has gained more attention in the current scenario. Among these, biochar is a promising filler material with its potential to replace commonly used inorganic fillers. The main objective of the present research is to determine the mechanical, thermal, dielectric, and flammability properties of hybrid composites made up of lotus fiber mate and waste biomass-based biochar from the Kigelia pinnata fruit shell (K. pinnata). The hybrid composites were fabricated using a hand layup process followed by compression molding, selected for their ability to enhance bonding and ensure uniform fiber and filler dispersion. Before fabrication, lotus fiber mats were chemically pretreated with 5 wt% of oxidant sodium chlorite (NaClO_₂) solution for 60 min. With varying the weight proportions of K. pinnata biochar and a constant weight proportion of lotus fiber, six types of composites were fabricated, such as A (pure epoxy), B (30 wt% of lotus fiber), C (fiber/2 wt% of biochar), D (fiber/4 wt% of biochar), E (fiber/6 wt% of biochar), and F (fiber/8 wt% of biochar) types. The results of the E-type composite sample reveal the highest mechanical properties. These included a tensile strength of 201 MPa and a modulus of 8.01 GPa; a flexural strength of 254 MPa and a modulus of 8.69 GPa; and an interlaminar shear strength of 41.1 MPa. The fire-retardant results showed that the inclusion of biochar greatly decreased the PHRR (356 kW/m² for B type and 154 kW/m² for F type) and the THR values (91 MJ/m² for B type and 70 MJ/m² for F type). The composite with the higher biochar concentration (8 wt%) exhibited an enhanced thermal conductivity of 0.46 W/mK. On the other hand, the dielectric constant and loss factor significantly rise when biochar and lotus fiber are mixed into an epoxy matrix. Based on the obtained results, there are several industries that might benefit from the conversion of waste biomass into biochar and composites, such as the aviation, automobile, and military industries.