Preparation and characterization of halogen-free flame retardants waterborne polyurethane co-modified with soft and hard segments

A novel waterborne polyurethane flame retardant, featuring co-modification with both soft and hard segments, was synthesized utilizing isophorone diisocyanate (IPDI), polyethylene glycol (PEG, Mn = 300), phosphorus poly alcohol (Exolit OP550), 2,2-dihydroxymethylpropionic acid (DMPA), phosphinylidynetrimethanol (THPO). The optimal conditions for the reaction were meticulously explored: 60 wt% OP550 in polyol, R  = 1.6, 10 wt% THPO, and 5 wt% DMPA in prepolymer. Under these conditions, the flame retardant effect was exceptionally ideal, achieving a limiting oxygen index (LOI) of 28 % for the latex film and an even higher LOI of 30 % for the treated polyester fabrics. TG-FTIR analysis demonstrated that FRWPU60 had a positive effect on the flame retardant performance in the gas phase. CONE analysis further revealed that FRWPU60 altered the burning mode of polyester at high temperatures exhibiting both condensed-phase and gas-phase flame retardant mechanisms. Specifically, the total heat release (THR) and peak heat release rate (HRR) values of the FRWPU60-treated polyester fabrics were lower than those of the control samples. Based on the comprehensive analysis results, we proposed the flame retardant mechanism. The mechanisms involved capturing radicals generated by combustion, synergistically promoting charring, and inhibiting heat transfer. These mechanisms collectively contributed to the exceptional flame retardant properties of the FRWPU60-treated polyester fabrics.