Multilayer chitosan/silica-coated ammonium polyphosphate flame retardants for enhanced fire resistance of thermoplastic polyurethane

This study, grounded in sustainable development strategies, developed a shell-core flame retardant by coating ammonium polyphosphate (APP) with multiple layers of polyelectrolytes composed of chitosan (CS) and silicon dioxide (SiO 2 ) through electrostatic interactions. The entire preparation process did not involve any organic solvents. The resulting APP@CS@SiO 2 -nBL (where “BL” denotes a bilayer structure of CS and SiO 2 , and “n” indicates the number of bilayers, ranging from 1 to 4) significantly enhanced the flame-resistant property of thermoplastic polyurethane (TPU). The TPU composite encompassing 20 wt% APP@CS@SiO 2 -4BL exhibited excellent thermal stability, where the maximum thermal decomposition rate declined by 21 % and the char residue elevated to 33.37 wt%. Additionally, this composite demonstrated superior performance in heat suppression and smoke reduction: the peak heat release rate, total heat release, peak smoke production rate, and total smoke release decreased 65 %, 86 %, 84 %, and 91 %, respectively, versus pure TPU. These enhanced properties relied on the multiple synergistic effects among APP, CS, and SiO 2 .