Preparation of Nitrogen‐Phosphorus‐Silicon Synergistic Intumescent Flame Retardant and Its Effect on the Flame Retardancy of Waterborne Polyurethane

ABSTRACT Waterborne polyurethane is widely used across various industries, including construction, automotive, leather, and thermal insulation, due to its exceptional properties such as lightweight, thermal insulation, and corrosion resistance. However, its susceptibility to combustion significantly limits its utility, highlighting the critical need for integrating flame retardants into polyurethane formulations. This study focuses on the synthesis of a novel hyperbranched flame retardant, HBNPSi, achieved by manipulating the proportions of 10‐(2′,5′‐dihydroxyphenyl)‐9,10‐dihydro‐9‐oxa‐10‐phospha‐phenanthrene‐10‐oxide (DOPO‐BQ), 1,3,5‐trihydroxyethylcazinone (THC), and isocyanatopropyltrihydroxyethylsilane (IPTS) as the constituent materials. The structural characteristics of the flame retardant were analyzed using infrared spectroscopy, carbon residue analysis, swelling height measurements, and x‐ray spectroscopy (EDS). HBNPSi was then incorporated as a reactive monomer in the pre‐polymerization reaction of aqueous polyurethane to produce a hyperbranched flame‐retardant polyurethane. The flame‐retardant properties were assessed through various tests, including oxygen index, vertical and horizontal combustion, thermo‐red in‐line, and cone calorimetry. Notably, the introduction of DOPO as a flame retardant in a ratio of BQ:THC = 2:1 resulted in an oxygen index of 29% and achieved a V‐0 flame‐retardant rating. Additionally, the decomposition temperature increased from 250°C to 300°C, while the heat release rate (HRR) decreased by 47.8%, total heat release (THR) decreased by 28.2%, and total smoke production (TSP) was reduced by 46.2%.