Flame retardancy and anti-impact performance of polyurea composite coating reinforced by modified ammonium polyphosphate and two-dimensional nano-fillers

The protection performance of polyurea (PUA) coating is limited due to its intrinsic flammability. In order to develop a PUA composite coating with outstanding flame retardant and anti-impact performance simultaneously, in this paper the modified ammonium polyphosphate (MAPP) and two-dimensional (2D) nanofillers of graphene oxide (GO) and Mg-Al layered double hydroxides (LDH) were introduced into PUA matrix. Thermal stability and combustion behavior of PUA composites were studied by thermogravimetric analyzer and cone calorimeter. Results show that PUA composite sample with 17 wt% MAPP, 1.5 wt% GO and 1.5 wt% LDH exhibited remarkable flame-retardant and fire protective performance. The flame retardancy index increases to 1.7 from 1.0 with the time required to burn out and total heat release THR being dramatically decreased by 31.0 % and 33.4 %, respectively. The dynamic mechanical properties of PUA composites at the strain rate as high as 4500 s⁻¹ were investigated. The dynamic mechanical behavior of the PUA composite shows strong strain rate effect. The introduction of the flame retardant does not substantially damage the energy dissipating capacity and anti-impact performance of the PUA matrix. Interfacial properties of PUA composites were studied by standard avulse and shear methods. The PUA composites with LDH and GO could form stronger bonding with the steel compared to neat PUA.