High-strength polyamide 66 composites enhanced with flower-like cellulose nanocrystals based flame retardant

Polyamide 66 (PA66), a key polymer in numerous industries, struggles with fire resistance in world spread, emitting toxic gases, smoke, and molten drips, with mechanical properties constrained by required high loading. Herein, we designed a flower-like bio-based three-hybrid flame retardant, synthesized cellulose nanocrystals (CNC) with melamine polyphosphate (MPP) and zinc borate (ZB) through successive grafting and electrostatic adsorption processes. This innovative fire-extinguish composite forms spherical arrangement structure within PA66, and noncombustible gas and protective phase on exposure to fire, significantly enhancing PA66's flame retardancy, mechanical properties, and UV resistance. Incorporating 15 wt% flame retardant, the PA66 composite remarkably improves LOI to 28.7 % and V-0, and reduces peak heat release rate to 210.56 kW/m², 75 % lower than neat PA66. Surprisingly, its mechanical properties were substantially improved with a 225 % and 317 % increase in tensile stress and tensile strain, respectively. This strategy has the potential to establish a fire-safe and highly efficient application environment for PA66, thereby ensuring the protection of human life and property.