Flame retardant and anti-dripping surface treatment through a co-deposition of polydopamine/polyphosphonamide for fabric and foam materials

High efficient flame retardant surface treatment through a simple and universal strategy has attracted considerable interest. In this work, polyphosphonamide (PPA) was synthesized via an eco-friendly amine ester exchange reaction, and then the polydopamine-polyphosphonamide (PDA-PPA) coating was constructed by a mussel-inspired phenol-amine co-deposition on the surface of various substrates (cotton, polyethylene terephthalate, poly (lactic acid), polyamide, polypropylene fabrics, and flexible polyurethane foam). It was demonstrated that the PDA-PPA coating significantly improved the flame retardancy of the six substrates. For example, in the case of PDA-PPA coated cotton fabric sample, the limiting oxygen index was increased to 28.3%, the peak of heat release rate and total heat release was decreased by 70.6% and 48.2%, respectively. Especially in the vertical and horizontal burning tests, all PDA-PPA coated samples were self-extinguished and free of molten droplets. It was suggested that the PDA-PPA coating released P-containing radicals to capture active small free radicals and released non-combustible gases to dilute combustible volatiles in the gas phase. In addition, the coating showed excellent intumescent charring ability and promoted the char formation of all substates except polypropylene. Surprisingly, the coating also improved the breaking strength of the PDA-PPA coated fabric and the compressive stress of the PDA-PPA coated foam samples. It was believed that this work provides a scalable and promising strategy for preparing fire safety polymeric materials with a large specific surface area.