Highly flame retardant and mechanical strong polyurea through synergistic effects of aromatic dianhydride and ammonium polyphosphate

Polyurea (PUA) elastomers have gained increasing attention in both defense and civilian fields due to its remarkable mechanical properties and protective capabilities. However, its high flammability significantly limits its application in many fields. It is challenging to achieve high flame retardant rating and maintain high mechanical properties simultaneously. Synergistic combination of different types of flame retardants is essential for this purpose. Herein we report a highly efficient synergistic combination of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and ammonium phosphate (APP) for flame retardance of PUA. BTDA contributes to excellent char-forming in solid phase, and APP contributes to radical scavenging in gaseous phase. By incorporating BTDA and APP as additive flame retardants in PUA, the melt dripping in combustion was entirely suppressed, and V-0 rating in UL-94 test was achieved. The heat release rate and the release of smoke and toxic gases were greatly reduced. Meanwhile, the mechanical properties of PUA were maintained very well. The PUA composites with outstanding flame retardancy and mechanical properties may serve as ideal protective materials in a variety of applications.