Effects of kaolinite on thermal, mechanical, fire behavior and their mechanisms of intumescent flame-retardant polyurea

In this work, kaolinite (K0) is addended into an intumescent flame retardant (IFR) for the purpose of enhancing the thermal stability, mechanical properties and flame retardancy of intumescent flame retarded polyurea (PUA/IFR) composites. The flammability, combustion behavior and linear ablation rate of PUA composites are explored by limiting oxygen index (LOI) and UL-94 vertical burning, cone calorimeter test and oxyacetylene ablation testing equipment, respectively. Results show that synergistic effect has been observed between K0 and IFR system, thus exhibiting well flame retardance and remarkable fire protective property of PUA/IFR/K0. When 1.0 wt% K0 was added (along with the remaining 24% IFR) in PUA/IFR composite, its LOI value increases to 36.0%, and the time to flame out and total heat release dramatically decrease by 32.0% and 16.0%, respectively. The tensile strength and elongation at break of PI-1.0K0 are enhanced by 4.8% and 36.9%, respectively, as compared with PUA/IFR. The underlying mechanism models of flame retardant and mechanical reinforcement for K0 are also explored. This work demonstrates the feasibility of employing K0 as synergist for IFR and indicates the promise of PUA composites in the field of aerospace acting as insulation.