Preparation and Properties of Bio-Based TA/APP Synergistic Intumescent Flame Retardant Polyurethane

An environmentally friendly intumescent flame retardant was developed by blending tannic acid (TA) and ammonium polyphosphate (APP), and intumescent flame-retardant polyurethane composites (IFR/TPU) were prepared via melt blending. The flame retardancy and mechanism of IFR/TPU were investigated through limiting oxygen index (LOI), cone calorimeter, and mechanical property tests. Results indicate that at a total exothermic flame retardant loading of 25 wt% and a TA:APP mass ratio of 1:1, IFR/TPU exhibits an LOI of 30.8%, achieving UL-94 V-0 rating, with a TG residue of 24.4%. The peak heat release rate (pHRR) decreased from 1102.46 kW/m 2 for pure thermoplastic polyurethane to 313.17 kW/m 2 . Furthermore, the incorporation of TA mitigated the adverse effects of flame retardants on the mechanical properties of TPU. SEM analysis of char residues revealed that TA promotes the formation of expanded carbon layers. This results in denser, more uniform char layers during combustion, enhancing both flame retardancy and smoke suppression. TA exhibits synergistic flame retardancy with APP. This approach maintains the inherent properties of polyurethane while delivering excellent flame retardancy, offering a novel design strategy for developing next-generation bio-based flame retardants.