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.