Accessible preparation of a novel nitrogen‑phosphorus synergetic nanocellulose-based flame retardant with excellent char-forming ability for enhancing the anti-melting droplet property of PA66

Developing eco-friendly and effective flame retardants is crucial for enhancing the fire resistance of polymeric materials. This study developed a novel nitrogen‑phosphorus (NP) synergistic nanocellulose-based flame retardant (CNC-PEI-PA) by grafting polyethyleneimine (PEI) and phytic acid (PA) onto the CNC. CNC-PEI-PA demonstrated remarkable thermal stability, char-forming ability, and antibacterial activity. Notably, the height of the intumescent char layer for CNC-PEI-PA increased by 700 %, and the char yield improved from 24.5 % to 45.0 % compared to CNC. Introducing CNC-PEI-PA into polyamide 66 (PA66) raised its maximum decomposition temperature to 470.0 °C and increased the char yield by nearly 330 %. More importantly, the quick formation of a dense intumescent char layer functioned as a robust protective barrier, enhancing the flame retardancy of PA66 while also greatly improving its anti-melting droplet property. The successful preparation of NP synergistic bio-based flame retardants through a facile and eco-friendly synthetic route shows their significant potential to enhance both the flame retardancy and anti-melting droplet properties of polymer materials.