Construction of TiO₂-based decorated with containing nitrogen-phosphorus bimetallic layered double hydroxides for simultaneously improved flame retardancy and smoke suppression properties of EVA

The addition of flame retardants is an efficient method to improve the flame retardancy and smoke suppression properties of ethylene vinyl acetate (EVA). However, the compatibility between the flame retardant and the matrix has a great influence on the flame retardant properties of the composites. In this work, a flame retardant with a core-shell structure (TiO₂@LDHs@PANI-PA) was designed and prepared, where titanium dioxide (TiO₂) was used as the core and nickel-cobalt layered double hydroxides (NiCo-LDHs) as well as phosphorus-doped polyaniline (PANI-PA) worked as a bilayer shell. The flame retardancy and smoke suppression of TiO₂@LDHs@PANI-PA are mainly attributed to the carbonization effect and the enhanced compatibility between the TiO₂@LDHs@PANI-PA and EVA matrix. The limiting oxygen index and UL-94 values of EVA/TiO₂@LDHs@PANI-PA composites reached a minimum of 30.2 % and V-0 when 10 wt% of TiO₂@LDHs@PANI-PA was added. The peak heat release rate, total heat release, and peak smoke production rate of EVA/TiO₂@LDHs@PANI-PA composites decreased by 50.9 %, 43.6 %, and 61.9 % compared with neat EVA. Furthermore, the improvement of flame retardant properties of the EVA/TiO₂@LDHs@PANI-PA composites is attributable to the catalytic function of Ni, Co, and Ti transition metal elements and the condensed phase flame retardant effect of the generated char residue during combustion. The results deepened our understanding of flame retardant mechanism.