Rare earth-based flame retardants for polymer composites: Status and challenges

Rare earth elements, the collection for 17 chemical elements in the third main group B on the periodic table of chemical elements, have received intensive attention in recent years. Based on the special electronic structure and physiochemical properties, rare earth elements are used as efficient flame retardants for polymers. Nowadays, various methods have been used for the synthesis of rare earth-based flame retardants, including precipitation, in situ polymerization and self-assembly methods. To date, zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) rare earth-based flame retardants have been developed to impart excellent fire safety to versatile polymeric materials, e.g. polyester, epoxy resin, polyurethane and polyolefin. The processing methods and flame retardancy of rare earth-based flame retardant/polymer composites are summarized. Subsequently, the flame-retardant mechanism of rare earth-based flame retardants in polymers is reviewed. Finally, the challenges and development prospects of rare earth-based flame retardant/polymer composites are discussed.