Introduction of Phosphorous to Metal-Organic Frameworks for Fire-Safe Polymers: From Synthesis to Application

Metal-organic frameworks (MOFs) are a class of materials with highly ordered porous structures. They are frequently utilized as flame retardants (FRs) to enhance the flame retardancy of polymers due to their distinctive high specific surface area, excellent porosity, and thermal stability. However, MOFs are often employed as synergists in combination with other flame retardants that possess superior flame retardant properties, owing to their limited effectiveness when used in isolation. Phosphorus flame retardants and halogen flame retardants are common primary flame retardants with recognized efficient flame retardant properties. A significant advantage of phosphorus flame retardants is that they emit fewer toxic gases during combustion, and they are widely used as a key component in modern polymer flame retardants due to their properties. A prominent trend in recent years has been the use of phosphorus flame retardants as the primary flame retardant in combination with the use of MOFs as synergists for polymer flame retardancy. This combination is more effective in improving the flame retardancy of polymers during combustion by, for example, catalyzing the formation of a denser carbon layer, while at the same time enhancing the dispersion of the filler in the polymer, thereby reducing the impact of phosphorus-containing FRs on mechanical properties. The utilization of such flame retardants is an emerging trend, as evidenced by numerous studies that have demonstrated their effectiveness. This paper examines the application of various MOFs-P FRs in different polymer systems, analyzing their impact on flame retardancy and mechanisms. It also compares MOFs-P FRs with other commercial phosphorus-based FRs, discusses the current state of it, and explores future applications and challenges.