Ecological Ammonium Thiocyanate-Modified Geopolymeric Coating for Flame-Retarding Plywood

An ecological ammonium thiocyanate (NH₄SCN)-modified geopolymeric coating was facilely prepared for flame-retarding plywood. The effect of NH₄SCN on the flame resistance was preliminarily investigated using cone calorimeter (CC), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermal gravimetry (TG). The results show that 1 wt.% NH₄SCN as dopant is of paramount importance to generate a compact and continuous coating. The formation of a smooth, intact, and uniform-swelling siliceous layer during combustion facilitates enhanced fire resistance, evidenced by the increased fire performance index (FPI), reduced fire growth index (FGI), and 39.7% decreased value of peak heat release rate (pHRR), in comparison to those of the sample without NH₄SCN. Because of the reducibility of O₂-consuming NH₄SCN, the compact shielding-layer containing carbonate and sulfate, as well as the release of NH₃, the NH₄SCN-modified geopolymeric coating exerts an enhancement on the flame-retardant efficiency.