A novel two-dimensional lamellar NP synergetic flame retardant for high-performance PA66: simultaneous fire safety, thermal insulation, and mechanical properties

The development of highly efficient flame retardants (FRs) is crucial for enhancing the fire safety of polyamide 66 (PA66). This study synthesized a novel two-dimensional lamellar nitrogen‑phosphorus (N P) synergetic FR (C-MATP) through covalent grafting of melamine (MEL) and electrostatic adsorption of aminotrimethylenephosphoric acid (ATMP) onto cellulose nanocrystals (CNC) in an organic solvent-free environment, and applied it to prepare high-performance PA66 composites. The CNC, MEL, and ATMP synergy enabled C-MATP to generate robust intumescent char and release significant inert gases, achieving effective flame retardancy. Remarkably, the addition of C-MATP endowed the PA66 with superior flame retardancy, smoke suppression, and anti-dripping performance through the synergy of condensed and gas phases. The limiting oxygen index (LOI) and UL-94 rating of P/10C-MATP composite reached 28.1 % and V -0, respectively, along with 48.3 % and 38.8 % reductions in the total heat release (THR) and total smoke production (TSP) compared with pure PA66. Moreover, the lamellar structure of C-MATP endowed the PA66 composite with excellent thermal insulation and mechanical properties, resulting in a 100 % increase in tensile strength and a 26 % increase in elongation at break compared to pure PA66. This study presents an innovative strategy for fabricating high-performance, multifunctional PA66 materials using novel, eco-friendly, and efficient FRs.