Fabrication of intrinsic flame-retarding rigid polyurethane foam with enhanced compressive strength and good thermal insulation

The rigid polyurethane foam (RPUF) with excellent flame retardancy, high compressive strength and good thermal insulation performance is of great importance to its widely application, especially the application in high-rise building exterior wall materials. In this work, two kinds of flame-retarding polyols (DADP and APDP) containing phosphorus and nitrogen elements were prepared via a simple salinization reaction and reacted into RPUF chains. When only 15 wt% of APDP was incorporated, the material passed the UL-94 V-0 rating with a limiting oxygen index (LOI) of 24.5% while 20 wt% of DADP incorporated to realize the same flame-retarding effect. For the RPUF/APDP15, the peak heat release rate (PHRR) decreased by 28.2% comparing to the neat RPUF and the fire growth rate (FIGRA) was the lowest 8.3, indicating the lowest flame spread speed among all the flame-retarding RPUF. The compressive strength of the RPUF/APDP15 material increased by 41.8% comparing to that of neat RPUF, mainly causing by the good compatibility and the enhancement of hardness of polyurethane via the benzene ring. Moreover, it was concluded that the gas-phase mechanism dominated in enhancing the flame-retarding effect for the RPUF material, and the APDP showed a higher flame-retarding effect with a higher content of phosphorus and nitrogen elements than that of DADP.