## 2 The Mechanism of EMA and Flame Retardant
### Flame Retardant  
A variety of testing techniques must be used in order to assess the performance of flame-retardant materials. The UL-94 vertical burning test, the limiting oxygen index (LOI), the cone calorimeter test (CCT), and infrared thermal imaging analysis are examples of common characterization techniques [57]. One important test technique for describing a material's flame-retardant qualities is CCT. It measures a number of crucial factors, such as heat release rate (HRR), total heat release (THR), TSP, and CO production rate (COP), and it models how materials would burn in a fire. These metrics fully reflect the flame-retardant capabilities of the material. A key measure of a material's flame-retardant properties, LOI testing determines the minimum oxygen concentration required to sustain burning. The ability of a material to sustain combustion generally declines as the LOI value rises. Examining a material's ability to extinguish itself and the behavior of molten droplets requires the use of the UL-94 test. With V-0 being the highest, the material is assessed based on its self-extinguishing qualities and droplet features during combustion (e.g., V-0, V-1, V-2). The temperature distribution on the material's surface during combustion can also be tracked in real time using infrared thermal imaging technology, which is crucial for assessing the material's thermal insulation qualities and flame spread behavior. Superior thermal insulation allows for infrared stealth capabilities, which are especially crucial in military and aerospace applications, in addition to efficiently preventing heat transfer.  
Because of their exceptional thermal stability, distinctive decomposition behavior, and capacity to adsorb and catalytically degrade combustion products, MOF-based composite materials have clear advantages in the field of flame retardancy [58]. Condensed-phase and gas-phase flame retardancy are the two primary fundamental mechanisms for flame retardancy [59; 60]. At high temperatures in the condensed phase, the metal ions in the MOF molecule break down, carbonizing the matrix material and forming a thick protective layer that effectively prevents oxygen and heat transmission [61]. Furthermore, composite materials including MOFs can collect pyrolysis products such as hazardous CO and carbon soot particles, resulting in much lower smoke and harmful gas emissions during burning [62]. MOF-based materials emit non-toxic or low-toxic volatile compounds (such as water vapor and CO\({}_{2}\)) during high-temperature decomposition, which contributes to gas-phase flame retardancy [63]. These gasses help reduce the amount of flammable gas in the combustion zone. Furthermore, active metal components (such as Fe, Co, Al, etc.) in some MOF composites can accelerate the production of hydroxyl or peroxyl radicals, interrupting the free radical chain reactions of combustion [64; 65]. Moreover, the thermal stability and flame-retardant qualities of MOFs can be improved by functional modification (for example, adding N, S, or P groups). Through cooperation with one-dimensional or two-dimensional (2D) materials (e.g., CNTs [66; 67; 68], layered double hydroxides [69; 70; 71], MXenes [72; 73; 74], etc.), MOF-based composites have been able to achieve notable increases in smoke suppression and flame retardancy.