Sustainable high performance basalt fiber reinforced composite with zero flammability

The transition to lightweight, fire-safe, and sustainable materials in automotive demands composites that simultaneously have mechanical performance, thermal stability, and zero flammability, requirements that are rarely met by conventional fiber-reinforced plastics composites. This study develops a high-performance, non-flammable polyamide 6,6 hybrid composite by integrating silane-treated basalt fiber, a non-halogenated flame-retardant (FR) and lignin-derived biocarbon as co-flame retardant synergist to engineer a densely constrained polymer-filler network. Basalt fibers provided stiffness enhancement, while silane modification significantly improved the fiber–matrix interface, resulting in improved tensile and flexural moduli of 9170 MPa and 9436 MPa, respectively. Incorporation of FR and porous lignin biocarbon generated an intumescent, carbon-rich protective layer that increased thermal stability (T_max = 445 °C, residue = 32.3%) and heat deflection temperature (240.4 °C). The hybrid architecture suppressed melt mobility and segmental relaxation, as evidenced by the damping factor, high storage modulus, low thermal expansion (31.47 µm/m·°C), a 60% reduction relative to neat PA66. The analysis of viscoelastic behaviour through modelling showed a high degree of entanglement between PA6,6 and reinforcement. Critically, the hybrid composite achieved a UL-94 V-0 rating with zero horizontal burn rate. The sustainable hybrid composite with a sustainable content of 35% directly addresses emerging automotive need for lightweight and fire-safe components such as battery housings, under-the-hood modules, and structural enclosures.