Reducing the fire toxicity of wood composites using hierarchically porous 4A (H4A) zeolite modified ammonium polyphosphate (APP) synthesized by a facile in-situ method

Abstract

Ammonium polyphosphate (APP) is considered an efficient fire retardant of wooden materials, but smoke and toxic gases will be released during the combustion of APP treated wood composites and, therefore, posing a severe threat to human life in practice. In this research, hierarchically porous 4A zeolite modified APP (H4A-APP) was synthesized by pretreating H4A zeolite with phosphoric acid (PA) followed by in-situ condensation with urea. H4A-APP treated wood composite were prepared, of which the flammability and fire toxicity were investigated. Thermal gravimetric analysis (TGA) indicated that the decomposition rate of H4A-APP was accelerated at low temperature, and the thermal stability of residue was enhanced significantly at high temperature. Compared with APP treated wood composite, H4A-APP treated wood composites showed 17.2% lower fire growth index at early stage (FGI1). The smoke production rate peak (SPRP) and CO production rate at 250 s (COPR250s) of H4A-APP treated samples were decreased by 35.2% and 38.4%, respectively. Further explorations of the microstructure and the chemical composition of the char residue were carried out, manifesting that besides the catalytic effect of H4A zeolite, the coherent surface and porous structure of the char residues with crosslinking structures like Si-O-P/C-Si played an essential role in reducing the fire toxicity.