Surface Regulation of Iron Phosphonate to Achieve Nanoscale Dispersion in Aqueous Flame-retardant System and Promote Carbonization of Cotton Fabric

The nano-synergist of metal organic phosphonate can promote the catalytic charring efficiency of phosphorus-containing flame retardant systems, but easy aggregation made it difficult to form a uniform dispersion and even distribution in the matrix. Herein, the organic iron phosphonate containing carboxyl and hydroxyl groups in the molecular structure (FeP) was firstly designed and synthesized. Then, FeP achieved nano-dispersion in APP aqueous solution at the molecular level through hydrogen bonding interaction between the carboxyl group and amino group, and the stable nano-dispersion (FeP/APP) was prepared. Next, intumescent flame-retardant coating (FeP/APP/PEI) was deposited on cotton fabrics using layer-by-layer assembly of FeP/APP and polyethyleneimine (PEI). The limiting oxygen index (LOI) of FeP/APP/PEI-4BL coated cotton increased to 28.0 %, which was 57.3 % higher than that of uncoated cotton. The char residues after cone calorimeter test (CCT) increased from 0 % to 18.8 %. The peak of heat release rate (pHRR) and total heat release (THR) dramatically decreased by 94.8 % and 81.0 %, respectively. The thermogravimetric coupled with Fourier transform infrared analysis (TG-IR) test indicated that the superior flame retardancy was attributed to the synergistic catalytic carbonization of nano-dispersed FeP and APP. The promotion of fire safety was ascribed to the formation of continue and protective char layer in condensed phase. Our work developed an aqueous suspension flame retardant system in which synergist could be uniformly dispersed at the nanometer level. It is especially suitable for promoting the catalytic carbonization and fire safety of cellulose-containing products.