Synergistic flame retardancy of aqueous hybridization between iron phosphonate and ammonium polyphosphate towards polyethyleneimine-based foam

Abstract

A hybrid flame retardant, of excellent stability in aqueous media, was designed to develop flame-retarded polyethyleneimine (PEI) foam. In this case, iron phosphonate (FeP) with carboxyl group and hydroxyl group was first designed and synthesized. The carboxyl group could be hydrogen bonded with the water-soluble ammonium polyphosphate (APP) in aqueous media, and then dispersed as nano-sized particles. Subsequently, the well-dispersed nano-hybrid of FeP and APP (FeP/APP) was blended with hydrophilic PEI to prepare a kind of composite foam through a freeze-drying process. For FeP/APP, the transition metal iron showed excellent catalytic carbonization performances. Meanwhile, APP could also catalyze the degradation of polymers to form a protective char layer. The thermogravimetric analysis coupled with Fourier transform infrared analysis (TG-FTIR) test disclosed that the improvement of flame retardancy for PEI-based foams was ascribed to the synergistic effect of FeP and APP in the condensed phase. The composite foam containing 30 wt% FeP/APP could self-extinguish and reach V-1 rating in UL-94 test. When the loading level of 45% FeP/APP reached 45%, the composite foam could elevate up to V-0 rating, and the peak of heat release rate and total heat release were reduced by 71.8% and 74.2%, respectively, compared to a neat PEI foam. It is worth noting that our work presents a promising way for preparation of stable aqueous flame retardant, and is expected to enhance the fire safety of aqueous foams, coatings, cotton textiles, and other flammable materials.