Phytic acid-Fe chelate cold-pressed self-forming high-strength polyurethane/marigold straw composite with flame retardance and smoke suppression

The applicability of wood-plastic composites has attracted great attention due to the improved sustainability. However, the fabrication of wood-plastic composites with excellent flame retardance and smoke suppression without compromising the mechanical property remains a great challenge. In this study, marigold straw (MS)-polyurethane (PU) composites (MPCs) were treated with phytic acid (PA) as a flame retardant and iron oxide (Fe2O3) as a smoke suppressor. The oxygen index of the proposed Fe/TMS (treated marigold straw)/PU/PA-10 composite was 27.8, and the total heat release was 12.02 MJ/m2. Fe2O3 and PA formed a mesh chelate in the form of a coordination bond, which provided a highly graphitized solid flame-retardant layer during the combustion process, improving the high-temperature stability of Fe/TMS/PU/PA-10. In addition, Fe2O3 can effectively catalyze the conversion of unsaturated gases, such as CO, into CO2. This is essential to suppress the smoke release and also avoid the production of toxic gases. The phosphate group of PA is cross-linked with the -NCO group of TDI (2,4-Toluene diisocyanate), thus significantly enhanced the physical properties of MPCs. This study provides an environmentally friendly approach to enhancing the flame retardancy and smoke suppression of MPCs.