A Schiff base-coated ammonia polyphosphate for improving thermal and fire-retardant properties of unsaturated polyester

Despite extensive applications in modern industry, unsaturated polyester resin (UPR) suffers intrinsic flammability, presenting fire threats to both environment and properties. Existing environmentally benign flame retardants, in particular ammonium polyphosphate (APP), often show a limited efficiency in UPR. Herein, a Schiff base-coated ammonium polyphosphate (MAPP) was synthesized using APP, 1,2-bis(2-aminoethoxy)ethane, and terephthalaldehyde (TPA). The results show that MAPP retards the initial decomposition of UPR and promotes its carbonization under heating, imparting enhanced thermal stability. Notably, 17 wt% of MAPP endows UPR with a UL-94 V-0 rating and a limiting oxygen index (LOI) of 28.6 %. MAPP is also effective in inhibiting heat and smoke release during combustion, and 17 wt% of it brings about 39.5 % and 18.0 % reductions in total heat release and total smoke production. Because of improved interfacial compatibility, the final UPR/MAPP displays significantly improved mechanical properties relative to UPR/APP. This work proposes a new functionalization surface modification strategy for creating efficient APP-based flame retardant for UPR, which is expected to be more widely applied in industries.