From frameworks to firewalls: metal-organic frameworks as smart additives for flame-retardant polymers

• MOFs, with their catalytic effects, enhance flame retardancy, thermal stability, char formation, and smoke suppression during the combustion of polymers. • Transition metals and rare earth metals are extensively reviewed for their application in MOF systems. • Multi-metal MOFs exhibit synergistic effects for superior fire resistance in polymeric composites. • Advanced MOF synthesis and functionalization strategies are critically evaluated. The increasing demand for polymeric materials that can be ‘safe’ during fire and combustion scenarios has led to a drive in the investigation of advanced flame-retardant systems that are both effective and environmentally friendly. Metal-organic frameworks (MOFs), a group of porous crystalline materials made up of metal centres (nodes) and organic linkers, have, in this case, shown great promise as multifunctional additives. This review investigates the role of MOFs in improving thermal and mechanical stability, catalytic properties, and flame retardancy of various polymer matrices. Different metal classes have shown to possess different properties that help in the improvement of polymeric materials’ flame retardance properties. Both transition metals (TM) and rare earth (RE) metals have been employed in MOFs, and studies show that TM exhibit higher thermal stability, thereby helping to prevent polymer degradation, whereas RE metals improve char formation and smoke suppression. Emphasis is also placed on the synergistic influence of metal selection, synthesis and the mechanisms by which MOFs increase Limiting Oxygen Index (LOI) values and improve Underwriters Laboratories (UL 94) tests, reducing heat release and material degradation during combustion. Through critically analyzing recent experimental findings and promising trends, this work highlights MOFs as leading additives in the creation of high-performance flame-retardant (FR) polymer composites.