Bisphosphoric modified amino functional [xFe3O4–2xAl(OH)3]/waterborne polyurethane nanocomposite with superparamagnetism and flame retardancy

Based on the strong adsorption of the diphosphate group to Fe and Al ions, first, the Fe3O4 and Al (OH)3 nanoparticles were modified by alendronate sodium (ALN), and organic phosphorus coated nanoparticles (Fe3O4‐ALN and Al (OH)3‐ALN) with the active group ─NH2 were prepared. Novel [xFe3O4–2xAl(OH)3]/waterborne polyurethane nanocomposite with superparamagnetism and excellent flame retardancy were prepared by in situ polymerization. The experimental results showed that when the content of Fe3O4‐ALN increased, the Ms increased. And the saturation magnetization reached 14.35 emu/g when the Fe3O4‐ALN content was 10 wt%. The nanoparticle network formed by Fe3O4 and Al (OH)3 can prevent the melting deformation of waterborne polyurethane (WPU) composite film and reduce the burning area. And the dual physical protective layer formed by nanoparticle network and char layer can prevent the combustible gas contacting with oxygen and giving off combustion heat, which effectively reduced the heat and smoke gas release. When the content of xFe3O4–2xAl(OH)3 was 20 wt%, the oxygen index of the composite was 28.4%, and the flame retardancy of nanocomposite was classified as V‐0 rating in the UL‐94 test.