Enhanced flame retardancy and mechanical properties of waterborne polyurethane based on the phosphorus and nitrogen containing polybutadiene acrylonitrile

To further improve fire resistance of waterborne polyurethane, the macromolecular intumescent flame retardant (APBDH) was designed and prepared from 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), 4‐aminothiophenol, benzaldehyde, and hydroxyl‐terminated polybutadiene acrylonitrile (HTBN). Then, it was incorporated into waterborne polyurethane (WPU) to preparing flame retarded WPU (FR‐WPU). TGA results suggested that the incorporation of APBDH into WPU increased thermal stability of FR‐WPU. The fire resistance of FR‐WPU were investigated by limiting oxygen index (LOI) test, the vertical burning test (UL‐94), SEM‐EDS analysis, the Laser Raman test, and cone calorimeter test. An LOI value of 28.82% and a UL‐94 V‐0 rating can be achieved when the WPU sample conjugated with 7.5 wt% APBDH. It indicated that the fire resistance of FR‐WPU remarkably improved and displayed both gas and condensed phase mechanism. As the content of APBDH increased, the tensile strength and the elongation at break of FR‐WPU increased firstly and then decreased. The thermo‐mechanical behaviors indicated that the storage modulus increase at first and then descend with the addition of APBDH, while the Tgs firstly decreased and then increased. Additionally, the Tgh increased with the addition of APBDH.