Construction of hierarchical structure of carbon nanotube-encapsulated ammonium polyphosphate/Mg(OH)₂ and the synergistic effect on the fire safety of ethylene-vinyl acetate copolymer

In this paper, a hierarchical structure of carbon nanotube-encapsulated ammonium polyphosphate (APP@CNT) flame retardant was synthesized, and Mg(OH)₂ was used in conjunction with nano-composite technology to prepare fire-safe wire and cable flame-retardant ethylene-vinyl acetate copolymer (EVA) composite material (APP@CNT/EVA-Mg(OH)₂). The structure and performance of flame-retardant ethylene-vinyl acetate composite materials were studied by using SEM, TGA, limiting oxygen index (LOI), vertical combustion (UL-94), microscale combustion colorimeter (MCC), universal stretching machine and high resistance meter. The results show that the residual carbon rate of EVA increases from 2.4% to 43.9%, the peak heat release decreases by 57.85% compared with pure EVA, the total heat release decreases by 57.80%, and the yield strength increases by 408%. At the same time, the volume resistivity of APP@CNT/EVA-Mg(OH)₂ is still as high as 3.9×10¹⁵ Ω·cm, indicating that the EVA composite material after flame retardant treatment is still an ideal wire and cable material. In addition, the oxygen index of APP@CNT/EVA-Mg(OH)₂ has reached 38%, and the vertical combustion UL-94 has also reached the V-0 level, which further illustrates the hierarchical structure of APP@CNT and magnesium hydroxide. Flame-retardant ethylene-vinyl acetate composite material has high fire safety performance.