Fabrication of inorganic coatings incorporated with phosphorus-nitrogen-functionalized graphene oxide nanosheets to improve waterborne polyurethanes fire retardancy

A new inorganic flame retardant P/N-GO was prepared by chemically modifying graphene oxide (GO) with phosphorus trichloride (POCl3) and 4,4-diamino-diphenylmethane (DDM). The P/N-GO was covalently grafted into a phosphorus-containing aqueous polyurethane (PWPU) system to prepare a flame-retardant nanocomposite (P/N-GO/PWPU). Due to the uniform distribution of P/N-GO in the polymer matrix, a strong interfacial adhesion can be formed and the mechanical properties of the WPU can be significantly improved. The mechanical strength of the composites increased from 4.56 MPa to 9.16 MPa. The LOI value of WPU increased from 25.5% to 30.5%, indicating that its flame-retardant properties were improved and met the standards for flame-retardant materials. At the same time, the peak heat release rate (PHRR) was reduced from 184.374 kW/m2 to 116.730 kW/m2, which showed good flame retardant properties of P/N-GO/PWPU and was favourable for expanding the application scope and safe use of WPU.