Sustainable and non-flammable hybrid composites based on ocean-recycled polyamide 6 reinforced with surface-modified basalt fiber and lignin-derived biocarbon

In this work, non-flammable and high-performance polyamide 6 (PA 6) hybrid composites with silane-treated basalt fiber, lignin-pyrolyzed biocarbon, ocean-recycled PA 6, and a low loading of non-halogenated flame retardant (melamine cyanurate) were prepared by melt extrusion followed by injection molding.

The silane-treated basalt fiber provided excellent stiffness, while lignin biocarbon produced at 950 °C imparted effective condensed-phase char formation. The synergistic hybrid reinforcement strategy significantly enhanced stiffness, heat stability and flame retardancy while maintaining good processability. The optimized hybrid composites with 10 wt% biocarbon and 20 wt% recycled PA 6 exhibited a 179% increase in tensile modulus and 194% increase in flexural modulus compared to neat PA 6.